OPERATION AND SERVICE MANUAL
Contents
1. i Fe 017 iaa ii 1 GENERAL DESCRIPTION uud 1 1 LL FEATURES 1 1 1 1 1 VERY WIDE FREQUENCY RANGE Ei 1 1 1 1 2 SUPPORT FOR VERY LOW HIGHLY DAMPED CRYSTALS 1 1 1 1 3 DIRECT REAL TIME MEASUREMENTS OF CRYSTAL FREQUENCY MASS AND RESISTANCE es 1 2 1 1 4 MULTIPLE CRYSTAL MEASUREMENT 5 rennes 1 2 1 1 5 ELECTRODE CAPACITANCE 1 2 1 1 6 AUTO LOCK nn essen es ee ee 1 2 1 1 7 CRYSTAL FACE ISOLATION zn eek 1 2 1 1 8 FULLY INTERGATED COMPUTER SOFTWARE 1 2 1 1 9 INPUTSANDOUTPUTSCABABILET Ys ds 1 3 LEIO DATA ACQUISITION CAPABILITY ati 1 3 1 2 CHARACTERIZING THE CRYSTAL MEASUREMENT 000000000000000000000000 1 3 1 21 FREQUENCY eis 1 3 172 FREQUENCY ERROR DUE TO PHASE ERROR nsien annesi nanan 1 3 123 FREQUENCY ERROR DUE TO IMPERFECT CAPACITANCE CANCELLATION 1 3 13 SPECIFICATIONS ss a dust N 1 5 1 3 1 CRYSTAL MEASUREMENT ee esse 1 5 12 DATA ACQUISITION ANALOG CARD 1 5 t FEN 1 5 32 2 Thermocouple Adalid 1 6 1323 ANA A ogee ee ne nies 1 6 E24 WR e taa paenitet dos 1 6 1 3 3 ee2. Bes 10 2 OCC 10 2 1023 IEIIERMOCOLFLEINPUT 10 2 10 3 GROUNDING CONSIDERATION 655260006 re 10 3 10 3 1 VOLTAGE MEASUREMENT GROUNDING 10 3 10 3 2 TEMPERATURE MEASUREMENT GROUNDING 10 3 yi 11 12 VO CARD OPTIONAL TROUBLESHOOTING GUIDE oi Table of Figures FIGURE 1 EQUIVALENT PHASE ERROR DUE IMPERFECT CAPACITANCE 1 4 FIGURE Z CRYSTAL CHANNEL DESCRIPTION zus 2 2 FIGURE 3 TYPICAL SYSTEM CONNECTIONS se eu eis 2 6 BERONT PANBE idad 2 7 FIGURES ROCNUREARDANE LE ia 2 8 FIGURE 0 MAXTER 1 INCH DIAMETER CRYSTALS ae aeg 3 1 FIGURE CRYSTAL ee needs nee 3 3 FIGURES CRYSTAL INSTALLA TON ad 3 4 FIGURE CRYSTAL HOUR ARE NT CIR OI 4 1 FIGURE LO POLAR PLOT OFCRYSTALADMITTANCE 2 4 2 FIGURE 11 ADMITTANCE VS FREQUENCY MAGNITUDE AND PHASE OF HIGH Q 5 4 3 FIGURE 12 ADMITTANCE VS FREQUENCY REAL AND IMAGINARY COMPONENTS OF HIGH Q CRYSTAL 4 3 FIGURE 13 POLAR ADMITTANCE PLOT OF HIGH Q 4 4 FIGURE 14 POLA
3. YOLVOICNI ALYY TVLSAMHO 300103713 JHL OL SLOSNNOO SNISNOH HOLOSANNOO JHL Xaou 19313 JHL OL SLO3NNOO Z LN3O IVLSAYO JHL OL SNOLLO3NNOO YOLOANNOO TVISAHO JONVLIDVAVI LNO ANNL OL JONVLIDWAWI ASHNOD TIVWS LNO ANNL OL JONVLIOWaAVO CNOLLVTT3ONVO JHL FTHM 03553 30 38 1511 NOLLNG SIHL YOLVOIGNI MOOT AHL NO SNANL ANY SLI OL ADNINOIYA 683 NAHM 12528 MAIA LNO 4 WILYVd NOOY JOVA IVLSAYI 2201 AJO Nn d33MS TWILISAdO iS5HVO2O Figure 2 Crystal Channel Description 2 2 UNDERSTANDING AND SETTING UP A CRYSTAL MEASUREMENT CHANNEL RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 2 2 GENERAL DESCRIPTION OF THE CRYSTAL MEASUREMENT The Maxtek Phase Lock Oscillator used on the Crystal Measurement Card was developed specifically to support the use of the quartz crystal microbalance in the measurement of lossy films and liquid applications addition to accurately tracking the frequency of heavily damped crystals the also tracks the crystal s resistance This provides additional information in the study of lossy films and or viscous solutions The PLO utilizes an internal oscillator referred to as a Voltage Controlled Oscillator
4. 5 1 ADJUSTING CAPACITANCE CANCELLATION TRIMMER 8 SWITCH Setting up the capacitance cancellation is fairly straightforward The thing to remember is that there are two adjustments a course rotary switch and a fine capacitor trimmer with the total compensation capacitance being the sum of the two The trim capacitor has no stops so it s not obvious when it 1s at its minimum or 1ts maximum The fine adjustment capacitor has circular rotor plates that mesh into fixed stator plates The capacitance 1s at a maximum when the plates are fully meshed and a minimum when rotor plates are above the stator plates and not meshed As the capacitor is rotated clockwise it goes through a full cycle from maximum to minimum and back to maximum Or depending on where you start it may go first toward a minimum then to a maximum and then back toward a minimum To avoid confusion we always want to be turning clockwise as we approach the desired capacitance and we want the capacitance to be decreasing ADJUSTING THE CAPACITANCE CANCELLATION RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE The coarse adjustment 1s a rotary switch Like the fine adjustment 1t goes from its minimum to 15 maximum then back to 1ts minimum capacitance value a full rotation The difference 1s that 1t has 16 positive stops Observe the V notch on the switch Figure 18 The coarse adjustment 15 at 1ts minimum capacitance when the notch 15 pointing straight upward
5. FINE CAPACITANCE COARSE CRYSTAL e SMB CABLE iN d bo nz 1 SWEEP UNLOCK LOCK O O O CRYSTAL FACE POTENTIOSTAT SMB TO BNC ADAPTOR NOT REQUIRED FOR OTHER HOLDER MODELS PARTIAL FRONT VIEW WORKING ELECTRODE TO ANALOG INPUT TO ANALOG INPUT NOTE THESE CONNECTIONS ARE REQUIRED FOR THE RQCM TO BE ABLE TO DATA LOG MASS AND CURRENT VERSUS POTENTIAL THE MUST EQUIPED WITH AN OPTIONAL DATA ACQUISITION CARD CRYSTAL HOLDER CHC 100 SHOWN COUNTER ELECTRODE REFERENCE ELECTRODE Figure 3 Typical System Connections 2 6 UNDERSTANDING AND SETTING UP A CRYSTAL MEASUREMENT CHANNEL RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE HO LIMS 15 5 6 SSLX EN EI AQVdH WALSAS daamMs TVISAHO 045 3SHVOO O sonar IV LSAJO WOO Naisn O ZLAVNO HI VISA 19530 8987 4331 5 NOLLVOINPININOO YALNANOD dYVOANVLS TINNVHO LNAWAYNSVAW TV LSASO JWNOILdO Y STANNVHO LNAWSAYNSVAW TVLSAYO Figure 4 RQCM Front Panel 2 1 CHANNEL UNDERSTANDING AND SETTING UP A CRYSTAL MEASUREMENT RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 3814 8 HOLOAISS HOLOINNOO OV YOLOINNOO JIYA Nid SZ TYNOILdO
6. Sensing Electrode exposed The Wrap Around Extended Electrode MUST be in the 60 region as Figure 8 below CRYSTALS AND HOLDERS 3 3 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE M 60 CRYSTAL M HOLDER Figure 8 Crystal Installation 3 Place the Retainer Ring over the Crystal with the Notch mating to the Index Pin 4 Mount and turn the Retainer Cover approximately 1 4 turn Then with a gloved finger or cotton swab gently press the Retainer Ring down at the Notch to make sure that it stays mated to the Index Pin Finish tightening the Cover until it s snug 3 4 CONSIDERATIONS FOR BUILDING YOUR OWN HOLDER You MUST consider the following aspects when you build your own crystal or holder The holder must be designed as such when a crystal 1s installed in it the crystal s front electrode sensing electrode 1s connected to the housing shell of the SMB Crystal Connector on the RQCM see Section 2 1 5 and the rear electrode 1s connected to the center pin of the SMB Crystal Connector The crystal should only be clamped as close as possible near the edge of the crystal to avoid damping of the crystal oscillation The holder clamping mechanism should have a positive stop to avoid stress of over clamping of the crystal 3 4 CRYSTALS AND HOLDERS RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE If the crystal 1s to be used in conductive fluid or conductive gas the rear electrode must be sealed from the conducti
7. A 5 1 MHz indicates a 5 1 to 10 MHz Replace crystal Crystal resistance exceeds the Replace crystal range of 5 and 5 000 Ohms Unit looses lock when crystal 15 Total capacitance of the crystal Adjust capacitance compensation exposed to liquid holder and cable changes when with crystal in the liquid Refer going from air to liquid to Section 5 Unstable frequency reading when Same as above The crystal Avoid contact with the hookup the crystal or the holder or the measurement 15 reacting to the during an experiment This 1s cable 15 being touched change in total capacitance when especially important if the crystal the setup 1s being touched 15 a low crystal Frequency reading is unstable or Temperature of the crystal 15 Control temperature of the test drifting changing An AT cut crystal environment frequency may drift as much as 10 Hz C Humidity level on the crystal is Control humidity of the test changing Moisture being environment absorbed or exuded from the crystal surface TROUBLESHOOTING GUIDE 12 1 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE Unbalanced or damaged Check cable for any signs of coaxial cable damage such as broken shield Replace cable Unit shows Lock with no The capacitance was probably This 18 normal Re connect the crystal holder and cable adjusted with the crystal holder crystal holder and cable connected to the crystal channel and cable combined
8. Period of uncoated crystal sec Note Units of are cm sec Note that the constant of proportionality this equation 15 constant This approach was demonstrated to be a significant improvement over frequency measurement and was widely adopted The original assumption that the addition of a foreign material to the surface of the crystal produced the same effect as that of the addition of an equal mass of quartz was of course questionable and indeed work with crystals heavily loaded with certain materials showed significant and predictable deviation between the actual measured film thickness and that predicted by equation 2 Analysis of the loaded crystal as a one dimensional composite resonator of quartz and the deposited film led to the equation below T T TK N 4 R e 3 Pr T where R is referred to as the Acoustic Impedance Ratio and is obtained by dividing the acoustic impedance of quartz by the acoustic impedance of the deposited film This equation introduces another term into the relationship which is the ratio of the acoustic impedance of quartz to the acoustic impedance of the deposited film The acoustic impedance is that associated with the transmission of a shear wave in the material Note that if the acoustic impedance ratio is equal to one quartz on quartz equation 3 reduces to equation 2 Although the above equation still involves a number of simplifying assumptions 15 ability to ac
9. X10 SIEMENS MAGNITUDE SPAN 200 DODHz Figure 11 Admittance vs Frequency Magnitude and Phase of High Q Crystal REF LEVEL DIV DUO 20 OODE 3 D 20 DODE 3 IMAGINARY SUSCEPTANCE X10 SIEMENS 60 CENTER 4 987 964 DODHz AMPTD 10 OdBm MARKER 4 987 964 OOO0Hz REAL UDF 114 94E 3 MARKER 4 987 984 DDOHz IMAGCUDF gt 5 8850E 3 REAL CONDUCTANCE X10 SIEMENS 140 120 100 80 60 40 20 SPAN 200 OOOHz 20Hz Figure 12 Admittance vs Frequency Real and Imaginary Components of High Q Crystal ELECTRICAL DESCRIPTION OF THE QUARTZ CRYSTAL 4 3 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE When the above complex conductance 15 plotted polar coordinates one obtains a circle as shown in Figure 13 The vector V indicates the magnitude and phase of the crystal current divided by the applied voltage The real part of the conductance 15 indicated by the vector R and the imaginary part is indicated by the vector I FULL SCALE 200 DOE 3 MARKER 4 987 955 500 2 PHASE REF 0 Odeg MAG UDF 115 3 REF POSN D Odeg PHASE CUDF gt D 092deg OSCILLATOR LOCK POINT gt N 2 OSCILLATOR 7 7 PHASE ERROR B AC OF 15 DEGREES Ps ae FREQUENCY 4 987966 MHz 8 60 WK IN nem v ZERO PHASE ERROR LOCK POINT TRUE SERIES RESONANCE CENTER 4 987 964 000 2 SPAN 200 DODHz AMPTD 10 OdBm XU T E S Sa sy X Figure
10. 3 2 DATA ACQUISITION ANALOG CARD OPTIONAL 1 3 2 1 Analog Inputs Note Except where noted All specifications 25 C All specifications are within 90 days of calibration Number of channels Resolution Selectable range Zero offset Gain accuracy Gain non linearity Single ended input impedance Differential input impedance Input protection Common mode range Common mode rejection 200V 70 dB up to 200 Hz GENERAL DESCRIPTION 1 5 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 1 3 2 2 Thermocouple Input Type thermocouple 010 371 C 2 sensor eror 1 3 2 3 RTD Input 00 0 Thin film platinum 0 10 600 C 1 3 2 4 Thermistor Input 100 0 to 150 C 1 3 3 I O CARD OPTIONAL Number of Discrete Inputs 8 ground true 4 7KQ pulled up to 5V Number of Discrete Outputs 8 SPST relays 120VA 2 A max 1 3 4 COMMUNICATIONS RS 232 serial port standard RS 485 serial port optional IEEE 488 optional 1 3 5 FRONT PANEL INDICATORS Communication Status LED s System Ready LED 1 3 6 POWER REQUIREMENTS 100 200 220 240 VAC 50 60Hz 25 W 1 3 7 PHYSICAL Size H including feet x 13 W x 9 4 D Weight 7 lbs Shipping Weight 10 lbs 1 6 GENERAL DESCRIPTION RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 1 4 ACCESSORIES Connector Connector Connector 603212 DB37S to Terminal Strip for Data ee 828007 Cable SMB Plug SMB Plug leng
11. common problems external to the If it is determined that the problem lies inside the unit please contact the factory for further assistance Symptom Possible Cause Line fuse blows when the power Wrong line voltage is selected at Set line voltage rear switch is switched to on the rear of panel to match with line voltage being used Incorrect fuse rating Replace line fuse with correct fuse size None of front panel LED Blown line fuse line fuse Replace fuse 00000 fuse indicators illuminated Power ci co MN is not on Switch front ics oc power switch to on No power being applied to unit Check and correct power source and or power cord Wrong line voltage is selected at Set line voltage on rear the rear of RQCM panel to match with line voltage being used Unable to adjust fine and coarse The total capacitance of the cable Adjust cable length to adjustments to compensate for crystal and crystal holder 15 out reduce increase its capacitance capacitance of range of 40 to 200 pfd Unit does not lock onto a Crystal fundamental frequency frequency when a crystal 1s exceeds the frequency range of installed the crystal channel Verify crystal frequency against crystal channel frequency range To verify the crystal channel frequency ranges press Reset button and observe the output A 3 8 MHz indicates the channel is set for 3 8 to 6 MHz
12. crystal frequency due to stress or temperature changes There are four important parameters that determine the frequency error of the PLO and sensing crystal system or indeed any oscillator and sensing crystal system The first two the zero phase error and the electrode capacitance cancellation errors are characteristics of the PLO The second two are characteristics of the crystal the Q of the crystal and the conductance 1 resistance of the crystal 1 2 2 FREQUENCY ERROR DUE TO PHASE ERROR Given some finite zero phase error the resulting frequency error depends on the sensing crystal s Q the higher the Q the lower the error For phase errors below 10 degrees the frequency error is 0 087 PPM per degree for crystals with a Q of 100 000 Thus a one degree phase error in the PLO results in a 0 44 Hz frequency error for a SMHz crystal with a Q of 100 000 For a 5 MHz crystal with a Q of 10 000 the error is 10 time greater or 4 4 Hz per degree Frequency Error deg df f PI 360 Q 1 2 3 FREQUENCY ERROR DUE TO IMPERFECT CAPACITANCE CANCELLATION The effect of imperfect electrode capacitance cancellation can also be viewed as an equivalent phase error This error 15 directly proportional to crystal resistance GENERAL DESCRIPTION 1 3 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE The equivalent phase error due to a non zero shunt capacitance equal to 1 15 one degree for a crystal with a series resistance of 556 Since the equ
13. phase error the Integrator output holds steady The integrator output 15 connected to the VCO Thus if the VCO frequency 1s initially below the crystal resonant frequency the phase will be positive producing a positive output at the phase detector This causes the Integrator output to climb which causes the VCO frequency to increase When the VCO frequency matches the resonant frequency of the crystal the phase will decrease to zero the phase detector output will go to zero the Integrator output will hold steady and the VCO frequency will be locked to the crystal s resonant frequency If the crystal s resonant frequency moves up or down a phase difference between the crystal voltage and current will develop producing a phase detector output The non zero phase detector output will drive the Integrator output up or down until the phase is zero once again thus keeping the VCO frequency locked to the crystal s resonant frequency Once the frequency of the VCO 1s locked to the series resonant frequency of the crystal the in phase component at zero phase error there is no out of phase component of the crystal current is demodulated to a DC voltage This voltage is amplified and converted into resistance value which the RQCM outputs to the computer UNDERSTANDING AND SETTING UP A CRYSTAL MEASUREMENT 2 3 CHANNEL RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 2 3 NORMAL OPERATION The RQCM comes set up for operation with a Max
14. stops The capacitance compensation adjustment 15 now complete Release the Reset button and assuming the crystal 15 not dead or out of range the will lock on 1t 5 2 WORKING WITH VERY LOW CRYSTALS Very low Q crystals require very close adjustment of the compensating capacitance to insure a successful lock To adjust the compensation capacitance one pushes the Reset button and adjusts the capacitance to the point where the Sweep LED just ceases to flash With very low Q crystals the PLO may not lock upon release of the Reset button The Unlock LED will be on and Sweep LED will be flashing This 15 normal Even so it may be possible to lock on the crystal by slowly adjusting the fine capacitance counterclockwise until Sweep LED again ceases to flash Lock 15 evidenced by the Lock LED turning on or by a crystal resistance of less than 10 Once lock 15 achieved the true series resonant point can be found by adjusting the capacitance for minimum resistance The limits of the crystal bandwidth can be determined by adjusting the capacitance and reading the maximum frequency and the minimum frequency just before the PLO loses lock ADJUSTING THE CAPACITANCE CANCELLATION 9 3 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 6 FREQUENCY ERRORS DUE TO IMPERFECT CAPACITANCE CANCELLATION There are two reasons that proper capacitance cancellation 15 so important with high resistance crystals The first 15 that to a first approx
15. t already done so Don t install the crystal at this point STATOR PLATES SILVER JUSTMENT PLATES GOLD 50 MESH COARSE ADJUSTMEN ROTARY SWITCH Figure 18 Capacitance Adjustments 9 2 ADJUSTING THE CAPACITANCE CANCELLATION RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE Set the course rotary switch to 1ts minimum Do not press the Reset button now rotate the course switch clockwise while watching the Lock and Unlock LED s The green Lock LED will come on when the capacitance 15 grossly out of adjustment Continue turning the course switch clockwise until the Unlock LED comes on The adjustment 15 getting close Press and hold the Reset button continue to turn the course switch clockwise At each stop observe the yellow Sweep LED at some point it will begin to flash If you continue to turn clockwise the Sweep LED will cease flashing but this 15 not the point you want Back off one stop so the flashing begins again The course adjustment 15 now complete Install a crystal into the holder Now depress and hold the Reset button Slowly adjust the fine trimmer clockwise until the flashing of Sweep LED just
16. terms of admittance Admittance 15 the inverse of impedance 1 Z thus the admittance reaches a maximum at resonance While impedance 15 proportional to the voltage developed across a device when it 1s subjected to a current the admittance 1s proportional to the current through the device when it 15 subjected to a voltage At any frequency the admittance of a quartz crystal is a complex value that can be expressed in terms of magnitude and phase or in terms of a real and imaginary value The relationship of these two representations 15 shown Figure 10 ELECTRICAL DESCRIPTION OF THE QUARTZ CRYSTAL 4 1 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE IMAGINA COMP OR QUA Figure 10 Polar Plot of Crystal Admittance ZAL COMPONENT Figure 11 shows the conductance in terms of magnitude and phase while Figure 12 shows the same information in terms of the imaginary and real part of the conductance 4 2 ELECTRICAL DESCRIPTION OF THE QUARTZ CRYSTAL RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE REF LEVEL DIV D O 20 OODE 3 Odeg 30 OOOdeg PHASE CENTER 4 987 964 DODHz AMPTD 10 OdBm a MARKER 4 987 964 000 2 MAG 115 64E 3 MARKER 4 987 964 DODHz 877deg PHASE UDF MAGNITUDE
17. the following formula Frequency Error 4 Phase Error in radians Bandwidth Or Frequency Error 1 2 57 3 Phase Error in degrees Bandwidth For the above ten ohm crystal the frequency error caused by a one degree phase error 15 42 114 6 or approximately 0 37 Hz For a one thousand ohm crystal one degree of phase error results in a 37 Hz error and for a ten thousand ohm crystal the frequency error is 370 Hz per degree of phase error Now the effective phase error caused by a non zero quadrature imaginary current 15 given by the following formula Effective Phase error arctangent imaginary current real current And since current 15 proportional to conductance Effective Phase error arctangent imaginary conductance real conductance The conductance of a one picofarad capacitor at 5 MHz is 31 4 microsiemens The conductance of a ten ohm crystal at resonance is 100 millisiemens FREQUENCY ERRORS DUE TO IMPERFECT CAPACITANCE 6 1 CANCELLATION RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE Effective Phase error arctangent 31 4e 6 100e 3 0 018 degrees In other words a one picofarad capacitance unbalance will result in an effective phase error of only 0 018 degrees when measuring a ten ohm crystal However when measuring one thousand ohm crystal the effective phase error will increase to 1 8 degrees and 1t will increase to 9 degrees when measuring a five thousand ohm crystal Combining these two errors we
18. unnecessary 9 2 RECOMMENDED MINIMUM COMPUTER CONFIGURATION Pentium 500 MHz PC e 24MB of RAM This 15 1n addition to the Operating System requirements e 35 of hard disk space Additional free hard disk space 15 required for data storage e CD ROM drive e Microsoft Windows 9x ME NT4 SP3 or later 2000 9 3 SOFTWARE INSTALLATION Follow the instruction below to install the software on the computer 1 Insert the RQCM Software CD into the CD ROM drive 2 If your system supports the auto run feature installation begins automatically 3 If your system does not support the auto run feature click Start Run then enter X setup where X is the CD ROM s drive letter 4 Follow the instructions in the windows as they appear 9 4 CREATING YOUR OWN SOFTWARE Although the RQCM includes a comprehensive Windows based interface program some users may find it necessary to create their own interface program This section describes the various computer interfaces and the protocol of the ROCM There are three types of computer interfaces offered The RQCM comes standard with an RS 232 serial interface Both RS 485 and IEEE 488 interfaces are available as options 9 5 RS 232 SERIAL INTERFACE The standard RS 232 serial interface of the RQCM allows one RQCM to be connected to any other device with an RS 232 serial interface The RS 232 interface port is the D9P COMPUTER INTERFACE 9 1 RQCM RESEARCH QUARTZ CRYSTAL MICR
19. zero position The capacitance 15 increased with each stop as the switch 15 rotated clockwise It reaches maximum capac tance at the 15 stop one stop before returning to the zero position If you bought Maxtek crystal holder and cable with your then you should not have to change the course adjustment Connect the cable and crystal holder to the SMB connector labeled Crystal but don t install a crystal If the Sweep LED is flashing press and hold the Reset button and then turn the fine tr mmer counter clockwise until 1t just stops flashing Go back and forth a few times to get a feel for the point where the Sweep LED just stops flashing Release the Reset button and the Sweep LED should begin to flash again Install a crystal The PLO should lock Even so press and hold the Reset button and again adjust the fine trimmer to the point where the flashing just stops The capacitance cancellation adjustment 1s now perfect Remember to check this adjustment whenever the crystal holder 15 moved or changed to a new environment If you could not find the proper zero capacitance point using the fine trimmer alone then we have found the following approach which 15 best for adjusting the coarse rotary switch First adjust the fine trimmer so that 1t is 50 meshed and the rotor plates are below the shaft You can see these plates through the oversize adjustment hole See Figure 18 Next connect a cable and crystal holder if you haven
20. 13 Polar Admittance Plot of High Q Crystal 4 4 ELECTRICAL DESCRIPTION OF THE QUARTZ CRYSTAL RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE FULL SCALE 2 SODOE 3 MARKER 4 986 414 DOOHz PHASE REF 0 Odeg MAG CUDF gt 1 5215E 3 REF POSN D Odeg PHASE UDF 13 518deg FREQUENCY 4 986414 MHz RESISTANCE 6570 Q 1 700 CRYSTAL MEASURED IN GLYCEROL AND WATER SOLUTION i gt CIRCLE FROMAIR TO SOLUTION RESISTANCE CHANGED FROM 8 6Q TO 6570 BT 4 984964 MHZ FREQ CHANGED FROM 4 987966 TO 4 987414 MHz e 526 Hz TRUE SERIES RESONANCE 4 986414 MHz EFFECTIVE PHASE ERROR CIRCLE BOTTOM 4 987914 MHz BANDWIDTH BOTTOM TOP CIRCLE 4 987914 4 984964 MHz 2 950 Hz CENTER 4 986 314 DOUHz SPAN 20 000 DOOHz AMPTD 10 OdBm Figure 14 Polar Admittance Plot of Low Q Crystal REF LEVEL DIV MARKER 4 986 314 000Hz 0 0 200 OOE 6 REAL UDF 1 3851E 3 200 DOOE 6 MARKER 4 986 314 000Hz IMAGINARY IMAG CUDF gt 363 72 6 SUSCEPTANCE F CONDUCTANCE 0 8 Lec AN I LL X10 SIEMENS _ l _ IIA aa LL ZU GE BEE LLLA LN LL LLL ae ea 0 CENTER 4 986 314 DODHz SPAN 20 000 DODH AMPTD 10 OdBm 2 KHz Figure 15 Admittance vs Frequency Real and Imaginary Components of Low Q Crystal 0 6 0 4 0 2 0 4 0 6 0 8 The condu
21. 7 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE Byte Description Length Range bytes Input 1 Range Input 2 Range Input 43 Range 6 Temperature Configuration Total Bytes 6 Each inputs voltage range and filter frequency can be independently configured There are four voltage ranges and two frequency ranges The available values are as follows The temperature configuration byte sets the units for the three temperature inputs A value of zero selects Fahrenheit and a value of seven selects Celsius Example To set inputs through 5 for 0 to 5 volt range and hertz filter and temperature inputs to Celsius computer would send Chr 255 Chr 254 Chr 1 Chr 2 Chr 6 Chr 0 Chr 0 Chr 0 Chr 0 Chr 0 Chr 7 Chr 240 4 Internal Command 5 Internal Command 6 Internal Command 7 Receive Relay Output Status Code 6 This instruction allows the computer to open or close relay outputs Each bit of the one byte command code in the message determines the status of one output If the bit is 1 then that output relay will close Ifthe bit is 0 then that relay output will open Bit 0 relay 1 bit 1 relay 2 etc For example To instruct the RQCM to close relays 1 amp 2 and open all other relays the computer would send Chr 255 Chr 254 Chr 1 Chr 6 Chr 1 Chr 3 Chr 245 9 8 COMPUTER INTERFACE RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 8 Internal Com
22. Chr 254 Chr 1 Chr 0 Chr 0 Chr 255 2 Automatic Data Logging of Binary Values Code 1 This instruction allows the computer to setup the RQCM to automatically output selected binary values to the communication port every 50 milliseconds The values sent are determined by the bit value of the message byte in the data logging instruction message Byte Bit Description Length Format Range Units bytes 1 0 Message counter 1 Binary 00225 J 1 Sensor l Period 4 j Binay Counts sec Binary A n Binary 6 Sensor 1 Resistance z o buy METE 6 Thermistor Temperature 3 0 1 The discrete input and output bytes indicate the status of the inputs and outputs such that bit 0 corresponds to input output 1 bit 1 to input output 2 etc Analog Input 5 RTD Temperature Thermocouple Temperature 33 333 to 33 333 All values are sent in Binary format with the most significant byte first To convert binary values to decimal use the following formula Decimal Value Sum of Byte n 256 Y 1 where n goes from to Y and Y is total number of bytes that make up the value 9 6 COMPUTER INTERFACE RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE For example say you want to read sensor frequency You first have to setup the RQCM to send sensor period Say you t
23. E UDF D 092deg NN TERRY es CENTER 4 987 964 DODHz SPAN 200 DODHz AMPTD 10 OdBm Figure 17 Non zero Phase Lock Figure 17 shows the result of a non zero phase lock Note that the frequency difference between the top of the conductance circle and the bottom 1s equal to the bandwidth of the crystal For a high Q high conductance low resistance crystal the bandwidth 1s very narrow and small errors in phase lock angle are insignificant For a low Q crystal the bandwidth can be quite large and small phase errors can result in significant frequency errors See the equations the error discussion section ELECTRICAL DESCRIPTION OF THE QUARTZ CRYSTAL 4 7 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 9 ADJUSTING THE CAPACITANCE CANCELLATION Proper adjustment of the Capacitance Cancellation is critical in obtaining accurate results with high resistance crystals See Section 6 The cancellation adjustment should be performed with the crystal holder and crystal in the measurement environment For instance if liquid measurements are to be made insert the crystal and its holder into the liquid where the measurement will be made With the crystal and holder in the measurement environment press and hold the Reset switch Pressing and holding the Reset switch forces the VCO to its minimum frequency turns on the Lock LED and turns off the quadrature current injector Forcing the VCO to its minimum frequency insures that the crystal 1s bein
24. LHOd NOISINDOY Y LWO HOLOJNNOO 3 Ivi 0 140d 88754 HO sa para z5 cECuH x 3nlss Yd ol E LED J11 1 SLL YA ER KERLEO TVNOILdO 887 3331 LHOd NOILISINDOVY VIVO HLIM SINOD HOLOJNNOO FIdANODONASHL L 1404 3gv I Gl po Figure 5 Rear Panel 2 8 UNDERSTANDING AND SETTING UP A CRYSTAL MEASUREMENT CHANNEL RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 3 CRYSTALS AND HOLDERS An essential part of the RQCM system 15 the sensing crystal The sensing crystal the crystal holder and the connecting cable must be orientated and connected correctly in order for the to work properly This 15 especially true f you design your own crystal or holder If you have purchased a Maxtek crystal holder and cable the installation 1s simple Follow the instructions below If you plan to build your own crystal or holder or cable see Section 3 4 3 1 1 INCH DIAMETER CRYSTALS Figure 6 below shows Maxtek 1 electrode patterns The left figure shows the front electrode also called sensing electrode with an extended electrode that wraps around the edge of the crystal and extends into a semicircle shown 1 the top half of the right figure T
25. M receives a message with an incorrect checksum it will disregard the message The checksum 1s the compliment of the one byte sum of all bytes from and including the instruction code to the end of the message If the one byte sum of all these bytes 1s added to the checksum the result should equal 255 If the sum of all bytes occupies more than one byte a single byte checksum can be generated using the expression checksum Sum MOD 2506 i e the checksum 15 the complement of the remainder byte which results from dividing the sum of all bytes by 256 9 9 DATATYPES There are three data types stored the One byte two byte and three byte parameters data types are stored as integers binary format with the most significant byte first The one byte data types are ASCII characters numeric values 0 255 or 8 bit registers Some of the multiple byte data types are decimal values stored as integers To convert these values to their decimal equivalent use the following equation Decimal Value Integer Value 10 DP 9 4 COMPUTER INTERFACE RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE Where DP the value s decimal point position The decimal point positions for all the parameters are constant and are given tables along with the parameters range 9 10 MESSAGE RECEIVED STATUS Following the receipt of each message the will send a one byte received status message indicating how th
26. MEN 1 6 1 3 4 COMMUNICATIONS tildado 1 6 1 3 5 FRONTPANEL INDICATORS a 8 0 in 1 6 1 3 6 POWER REQUIREMENTS sa in 1 6 1 3 7 PHYSICA ne M 1 6 L4 ACCESSORIES iio 1 7 IS OPTIONAL CARDS sans Bu seems 1 7 2 UNDERSTANDING AND SETTING UP A CRYSTAL MEASUREMENT CHANN A 2 1 2 1 BRONTE PANEL DESCRIP DION ic 2 1 2 1 1 EOERINDIERTOR do dae al 2 1 2512 VO N 2 1 2 1 9 SWEEP RATE INDICATOR beet e Bele 2 1 2 1 4 RESET ATEO o di 2 1 2 15 ERYSIAECONNECHOR ae 2 1 2 1 6 CRYSTAL FACE CONNECTOR lt lt ds 2 1 2 2 GENERAL DESCRIPTION OF THE CRYSTAL MEASUREMENT 2 3 2 9 NORVMAE OPERATION 2 868508 ee 2 4 2 5500 RR 2 4 2 CRISTALS AND HOLDERS nass 3 1 3 DIAMETER CRYSTALS iiisieistsebebvs RR EBRRE epe Eo Tee 3 1 32 CRYSTAL HOEDERS a 3 2 33 HOW TO INSTALL A CRYSTAL IN A CRYSTAL HOLDER 3 3 34 CONSIDERATIONS FOR BUILDING YOUR OWN HOLDER 3 4 4 ELECTRICAL DESCRIPTION OF THE QUARTZ CRYSTAL 4 1 5 ADJUSTING THE CAPACITANCE CANCELLA TION e ecce eere 5 I 51 ADJUSTING CAPACITANCE CANCELLATI
27. MICROBALANCE 7 CALCULATING CRYSTAL POWER Crystal power can be calculated as follows Crystal power Pery i Ra Crystal current 1 Voc Rs Rery Hence Pery i Ro Vo Rs Ray Where Voc Open Circuit crystal drive voltage 125 mV R Crystal drive source resistance 20 ohms Roy Crystal resistance value in ohms Examples 1 Crystal Resistance 80 ohms Pery in watts 0 125 20 80 80 1 25E watts or 125 2 Crystal Resistance 4000 Pory in watts 0 125 20 4000 4000 3 87E watts or 3 87 LW CALCULATING CRYSTAL POWER 7 1 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE Crystal Power vs Crystal Resistance 250 200 150 100 Crystal Power uW 50 10000 456 224 144 103 7 6 5 4 3 3 2 2 1 1 1 1 Crystal Resistance ohms Figure 20 Crystal Power Dissipation vs Crystal Resistance 7 2 CALCULATING CRYSTAL POWER RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 8 FILM THICKNESS CALCULATION Early investigators noted that if one assumed that the addition of material to the surface produced the same effect as the addition of an equal mass of quartz the following equation could
28. OBALANCE connector on the rear panel of the RQCM The pin layout 1s shown in Figure 21 and Table lists the pin signal assignments including a definition of whether the signal is input or an output of the RQCM The RQCM acts as and accordingly 9 pin connector has plug pins It can be used with a DCE or a DTE host cable connection providing the sense of the RxD TxD data lines and the control lines 1s observed Pin 2 TxD transmits data from to the host pin 3 RxD receives data from the host Pin 7 CTS is a control output signal and pin 8 RTS 1s a control input signal In this implementation pin 7 CTS means what 15 says namely this is an output control line and when asserts this control line true the host can transmit to the On the other hand pin 8 RTS is not quite what it may seem because this 1s a signal input to and it is intended that the host should assert this line true only when the RQCM 1s allowed to transmit data to the host The RQCM does not generate an RTS request to send as such for the host PC so the host should assert pin 8 true whenever the RQCM is allowed to transmit to the host without being asked to do so The RQCM s RS 232 port is automatically set up to operate with the following specifications 19200 Baud 8 Bit data No Parity 1 Stop bit Figure 21 D9S DTE Rear panel RS 232 socket c
29. ON TRIMMER SWITCH 5 1 5 2 WORKING WITH VERY LOW Q CRYSTALS eere eee eee ee eee eene eee 5 3 6 FREQUENCY ERRORS DUE TO IMPERFECT CANCELLATION A 6 1 C CALCULATING CRYSTAL POWER A 2 1 amp FILM THICKNESS CALCULATION uses 6 1 9 COMPUTER JNTEREAGCE 9 1 91 COMPUTER INTERFACE SOFTWARE eeeeeee 9 92 RECOMMENDED MINIMUM COMPUTER CONFIGURATION 9 1 9 3 SORTWARETNSTALLATION au neh ee 9 1 9 4 CREATING YOUR OWN SOFTWARE cccccccccccccccccccsccscsccccccccsssccsssssssees 9 1 95 lt 5 252 SERIAL INTERFACE id 9 1 96 RS 485 SERIAL INTERFACE seen 9 2 9 7 IEEE 488 PARALLEL INTERFACE cainnean aaeoa e eSa 9 3 9 5 PROTOCOL novit ds 9 4 99 DATA E 9 4 9 10 MESSAGE RECEIVED STATUS Poe e eee oap ia ap oS ooa aaeoa idosas 9 5 9 11 E 9 5 9 12 5 255 ie 9 5 I0 DATA ACQUISITION CARD OPTIONAL ecce eee ee eee ee ee erento 10 1 10 1 255 10 1 10 2 TEMPERATURE INEUI S tee een P TUR 10 2 1024 THERMISTOR INPUT oea
30. OPERATION AND SERVICE MANUAL R QC RESEARCH QUARTZ CRYSTAL MICROBALANCE SYSTEM READY MAXTEK INC www Maxtekinc com 11980 Telegraph Road Santa Fe Springs CA 90670 Tel 562 906 1515 e Fax 562 906 1622 Email Sales Maxtekinc com Support Maxtekinc com OPERATION AND SERVICE MANUAL RO C Mi RESEARCH QUARTZ CRYSTAL MICROBALANCE IEEE 488 TR TXD XD TS O LISTEN RQCM CRYSTAL MICROBALANCE O SRQ O SYSTEM READY N MAXTEK INC P N 603800 S N INC www Maxtekinc com 11980 Telegraph Road Santa Fe Springs CA 90670 Tel 562 906 1515 e Fax 562 906 1622 Email Sales Maxtekinc com Support Maxtekinc com 2002 INC All rights reserved First Edition March 2002 Revision A May 2002 Revision B October 2002 Revision C December 2002 WARRANTY Maxtek Inc warrants the product to be free of functional defects material and workmanship and that it will perform in accordance with 165 published specification for a period of twenty four 24 months The foregoing warranty 1s subject to the condition that the product be properly operated in accordance with instructions provided by Maxtek Inc or has not been subjected to improper installation or abuse misuse negligence accident corrosion or damage during shipment Purchaser s sole and exclusive remedy under the above warranty 1s limited to at M
31. R ADMITTANCE PLOT OF LOW CRYSTAL eese eene nennen nennen nennen nant 4 5 FIGURE 15 ADMITTANCE VS FREQUENCY REAL AND IMAGINARY COMPONENTS OF LOW CRYSTAL 4 5 FIGURE 16 ADMITTANCE VS FREQUENCY MAGNITUDE AND PHASE OF LOW CRYSTAL 4 6 FIGURE NONSZBRO PEASE LOCKS ee esse 4 7 FIGURE IS CAPACITANCE ADIJUSTMENTS N ee 5 2 FIGURE 19 FREQUENCY ERROR DUE IMPERFECT CAPACITANCE CANCELLATION 6 2 FIGURE 20 CRYSTAL POWER DISSIPATION VS CRYSTAL 6 5 4 6000000 0 7 2 FIGURE 21 095 DTE REAR PANEL RS 232 SOCKET CONNECTOR 9 2 FIGURE22 CONNECTOR a dd 9 3 FIGURE 23 DB25P DATA ACQUISITION REAR PANEL 0 10 1 FIGURE 24 REAR PANEL TYPE THERMOCOUPLE 2 10 3 FIGURE 25 DB73P REAR PANEL CONNECTOR data 11 1 vil RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 1 GENERAL DESCRIPTION The RQCM is designed for many types of research applications where Quartz Crystal Microbalance measurement is desired Included with each instrument 15 a Windows based software package that allows the user to configure the RQCM setup multiple experiments log data with real time graphing and review res
32. VCO to drive the crystal The crystal current is monitored and the frequency of the oscillator is adjusted until there is zero phase between the crystal voltage and current Assuming that the crystal s electrode capacitance has been effectively cancelled this point of zero phase between the crystal current and voltage is the exact series resonant point of the crystal The magnitude of the current at this point 1s directly proportional to the crystal s conductance This current is monitored by the RQCM and displayed as crystal resistance The PLO contains a phase detector that continuously monitors the phase difference between the crystal s current and voltage At frequencies below the crystal s resonant frequency the current leads the voltage and the phase goes to 90 degrees as the frequency separation continues to increase see Figure 12 Above the resonant point the current lags the voltage and the phase go to minus 90 degrees As the frequency increases through the resonant frequency the phase goes from plus 90 through 0 to minus 90 It 15 interesting to note that the phase angle 15 45 degrees when the VCO frequency 15 one half of the crystal s bandwidth above or below the crystal s resonant frequency The output of the phase detector 15 fed into an integrator The integrator accumulates the phase error such that any positive phase error causes the integrator output to climb a negative phase causes the integrator output to fall With zero
33. With everything removed the Lock light just means that the capacitance 1s now grossly out of adjustment Unit shows Lock but the An electrical short across the Check the cable holder and the frequency reading 15 at 1ts lowest crystal input crystal for short Remove short and the resistance reading 15 or replace the defective part about 1 ohm No Clear to Send Signal error Wrong COMM port number Set the correct COMM port message when attempting selected number in the Setup Comm communications with RQCM Setting Menu RS 232 Cable not connected to Connect RS 232 cable to ROCM Error reading data message Wrong COMM port number Set the correct COMM port Timeout when attempting selected number in the Setup Comm Port communications with ROCM Setting Menu Incorrect RQCM Interface Set an Interface Address in the address Setup Comm Port Settings Menu and click the Send Address button to send to ROCM COMM port not enabled Enable COMM port in PC s BIOS 12 2 TROUBLESHOOTING GUIDE
34. axtek s option repair or replacement of defective equipment or return to purchaser of the original purchase price Transportation charges must be prepaid and upon examination by Maxtek the equipment must be found not to comply with the above warranty In the event that Maxtek elects to refund the purchase price the equipment shall be the property of Maxtek This warranty is in lieu of all other warranties expressed or implied and constitutes fulfillment of all of Maxtek s liabilities to the purchaser Maxtek does not warrant that the product can be used for any particular purpose other than that covered by the applicable specifications Maxtek assumes no liability any event for consequential damages for anticipated or lost profits incidental damage of loss of time or other losses incurred by the purchaser or third party in connection with products covered by this warranty or otherwise DISCLOSURE The disclosure of this information 15 to assist owners of Maxtek equipment to properly operate and maintain their equipment and does not constitute the release of rights thereof Reproduction of this information and equipment described herein 15 prohibited without prior written consent from Maxtek Inc 11980 Telegraph Road Santa Fe Springs CA 90670 WARNING Only properly trained personnel should attempt to service the RQCM Table of Contents OPERATION AND SERVICE MANUAL lt lt ROH
35. be used to relate the film thickness to the change in crystal frequency TK Pe 2 1 f n f where N Frequency constant for an AT cut quartz crystal vibrating in thickness shear Hz x cm N 1 668 x 10 Hz x cm p Density of quartz g cm fa Resonant frequency of uncoated crystal f Resonant frequency of loaded crystal Tks Film thickness pr Density of material g cm This equation proved to be adequate most cases however note that the constant of proportionality 1s not actually constant because the equation contains the crystal frequency which of course changes as the film builds up Because the achievable frequency change was small enough the change scale factor fell within acceptable limits Improvements in sensor crystals and oscillator circuits resulted in a significant increase in achievable frequency shift Low cost integrated digital circuits became available allowing a significant increase in basic instrument accuracy As result of the above two factors the frequency squared term in the scale factor became a significant limitation on the measurement accuracy If the period of oscillation is measured rather than the frequency l period can be substituted for frequency resulting 1n the following equation 2 e where FILM THICKNESS CALCULATION 8 1 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE T Period of loaded crystal sec T
36. can get an idea of the magnitude of the frequency error caused by imperfect capacitance cancellation For a 10 Q crystal one picofarad capacitance imbalance results in a 0 018 degree phase error and a 0 0067 Hz frequency error For a 100 Q crystal the phase error 1s 0 18 degrees and the frequency error 1s 0 67 Hz For a 1000 Q crystal the phase error 1s 1 8 degrees and the frequency error 1s 67 Hz For a 5000 crystal the phase error 15 9 degrees and the frequency error 15 1 635 Hz A two picofarad capacitance imbalance will result in approximately twice the above error Frequency Error vs Crystal Resistance 100000 000 10000 000 1000 000 100 000 10 000 Freq Error due to a 5 pfd capacitance imbalance Frequency Error Hz 1 000 Error due to a 0 100 2 pfd capacitance imbalance Freq Error due to a 1 pfd capacitance imbalance IS 0 010 0 001 00 o LO LO LO N 10 000 6 310 3 981 2 512 1 585 1 000 Crystal Resistance ohm Figure 19 Frequency Error Due to Imperfect Capacitance Cancellation 6 2 FREQUENCY ERRORS DUE TO IMPERFECT CAPACITANCE CANCELLATION RQCM RESEARCH QUARTZ CRYSTAL
37. ctance of the L R C series arm creates the circle in the polar plot with its center on the real axis The effect of the shunt capacitance conductance 15 to offset the circle vertically Figure 14 shows a heavily loaded crystal in which the offset 1s obvious It is the imaginary quadrature current through the shunt capacitance that creates the ELECTRICAL DESCRIPTION OF THE QUARTZ CRYSTAL 4 5 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE offset The RQCM provides a mechanism for canceling out the imaginary current effectively putting the center of the crystal back on the real axis The true series resonant frequency of the crystal 1s then the point where the conductance circle crosses the real axis This is the frequency at which inductive and capacitive impedance s in L amp C branch cancel out and the crystal looks like a pure resistance of value REF LEVEL DIV MARKER 4 986 314 DODHz O 200 OOE 6 MAG UDF 1 5398E 3 D Odeg 30 000deg MARKER 4 986 314 ODOHz PHASE UDF 16 983deg MAGNITUDE X10 SIEMENS c r AAA ENNNNEA AAA Mer CENTER 4 986 314 ODOHz SPAN 20 000 DODHz AMPTD 10 DdBm Figure 16 Admittance vs Frequency Magnitude and Phase of Low Q Crystal 4 6 ELECTRICAL DESCRIPTION OF THE QUARTZ CRYSTAL RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE FULL SLALE 200 DOE 3 MARKER 4 987 966 500 2 PHASE REF 0 Odeg MAG CUDF 115 3 REF POSN 0 Odeg PHAS
38. curately predict the film thickness of most commonly deposited materials has been demonstrated The basic measurement is period which can be thought of as a measurement of equivalent quartz mass The actual film mass on the crystal is then found by applying the acoustic impedance correction factor When the thickness indication is zeroed the initial equivalent quartz mass and the initial corrected film mass are stored For each subsequent measurement the new corrected total film mass is calculated and the film mass deposited since the thickness was zeroed 15 determined by subtracting the initial corrected film mass from the total corrected film mass The film thickness on the crystal is calculated by dividing by the film mass by the material density 8 2 FILM THICKNESS CALCULATION RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 9 COMPUTER INTERFACE Three different interfaces are available to connect the RQCM hardware to your computer The RQCM system comes standard with an RS 232 serial interface Both RS 485 and EE E 488 interfaces are available as options Currently does not offer Universal Serial Bus USB interface However you can use an inexpensive RS 232 to USB adaptor 1f your computer does not have an RS 232 port available Refer to the Data Logging on line help for more details 9 1 COMPUTER INTERFACE SOFTWARE Y our RQCM software 15 supplied a CD Extensive on line help makes a hardcopy manual
39. e Thermistor P N 44006 or equivalent Shielded twisted pa r 15 recommended for the leads This thermistor has a range of 0 to 150 C The use of a thermistor provides high accuracy measurements within 1ts temperature range or when long leads are required 10 2 2 RTD INPUT The RTD has a range of 0 to 600 C The use of the RTD 15 for the measurements in the higher temperature ranges The RTD input is designed to use an RTD conforming to the European standard curve with an alpha of 0 00385 for the Calendar van Dusen equation and a resistance of 100 ohms 0 C The RTD is connected as a four wire element using a pair of wires for excitation and pair of wires to sense the voltage across the element This configuration should be continued all the way to the probe for maximum accuracy A single shielded cable with two twisted pairs or two shielded twisted pair cables should be used 10 2 3 THERMOCOUPLE INPUT The Type T Thermocouple input uses true internal cold junction compensation For accurate measurements thermocouple grade copper and constantan wire must be used from the thermocouple to the rear panel thermocouple connector Figure 24 shows the rear panel thermocouple connector The mating connector 15 an Omega NMP T M included with each Data Acquisition Card or equivalent If it is desired to use shielded thermocouple wire which is recommended the shield drain wire can be connected to the RTD or thermistor shield pin The Ty
40. e message was received with the following format Header Address Inst 253 Length 2 Instruction Code Receive code Checksum A value of 253 for the instruction byte indicates that this is a received status message The Instruction Code byte indicates the instruction code of the message that was received The following table shows a list of possible receive codes 0 Message received Invalid checksum 9 11 INSTRUCTION SUMMARY The following table 15 a list of valid instruction codes SN Send configuration oo 1 lmitiateautomatie data logging of binary values Internal command OOOO Internal command Internal command 9 12 INSTRUCTION DESCRIPTIONS The following 1s a description of the valid instructions along with an example of how they are used All the examples assume the device address 15 1 COMPUTER INTERFACE 9 5 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 1 Send RQCM hardware configuration Code 0 Instructs RQCM to send its configuration data to the host computer The following 15 a description of the configuration data message Length bytes Maxtek RQCM Software Version X XX 1 RS232 2 RS 485 3 IEEE488 1 Sensor Board Status 1 Bit0 Ch l Bitl Ch 2 Bit2 Ch 3 Accessory Board Status 10 Digital I O Bit 1 Analog Input Total 38 bytes Example To instruct the to send the configuration data the computer would send Chr 255
41. ent injection which is require for proper capacitance cancellation adjustment The equivalent of about 1 5 pfd of capacitance is added as quadrature current to insure that the VCO ramps up in frequency when not locked onto a crystal The quadrature current is turned off as soon as a lock is detected 2 1 5 CRYSTAL CONNECTOR The SMB connector labeled Crystal provides connections to the crystal When used with a Maxtek crystal holder the center pin connects to the crystal s rear electrode and the connector housing connects to the crystal s front electrode 2 1 6 CRYSTAL FACE CONNECTOR The Crystal Face connector provides a connection to the crystal s front electrode when used with a Maxtek crystal holder When this connection is not used the crystal face electrode is grounded When the mating connector 15 inserted the crystal face electrode is disconnected from ground allowing a potential to be applied For example you can connect the crystal face electrode to the working electrode of a potentiostat for electrochemical experiments UNDERSTANDING AND SETTING UP A CRYSTAL MEASUREMENT 2 1 CHANNEL RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 300419373 9NIMMOM IVLSAYO JHL OL LNSWNYLSNI WOINSHOOU LOSTA NV OL NOLLO3NNOO YOW YOLOANNODS 39V 4 N33H9 MOLVOIONI 1907 HOLVOIONI ADO INN 1 3QNf SI 32NVLIOVdVO TVLSAMD JHL S31VOIONI ONIHSV T3 NAHM
42. g driven at a frequency far from its resonant frequency where its impedance 15 essentially due only to the shunt electrode capacitance With the quadrature current injector turned off the measured current is due only to the net shunt capacitance The measured net shunt capacitance 15 the capacitance of the cable holder and crystal electrodes minus the compensation capacitance If the capacitance 1s under compensated the phase of the measured current leads the voltage a phase angle of plus 90 degrees If the capacitance 15 over compensated it lags the voltage a phase angle of minus 90 degrees The Yellow Sweep LED is used to determine whether the crystal capacitance is over compensated or under compensated The Sweep LED flashes whenever the crystal capacitance in under compensated If the Sweep LED 15 not flashing turn the fine compensation clockwise until it begins to flash then back up until it just stops If it is flashing turn the fine adjustment counter clockwise until it just stops flashing This 15 a very fine adjustment Go back and forth until you are sure you are right on the edge The sensitivity of the fine adjustment is approximately 0 05 pfd per degree In situations where the crystal resistance 1s very high over 1 KQ a net capacitance of over 0 5 pfd can result in a significant frequency error so try to get this adjustment to within a couple of degrees Remember to keep the Reset switch depressed while making this adjustment
43. he four following bytes representing sensor period 31 255 109 53 This equals 31 256 3 255 256 2 109256 53 536 833 333 To convert period to frequency use the following formula Frequency Hz 3 221E15 Period 3 221 15 536 833 333 6 000 000 0 Hz Like sensor period sensor resistance 15 also special units Use the following formula to convert the resistance counts value sent by the RQCM to OHMs Sensor Resistance OHMs 273 300 Counts 20 The scaling of the analog inputs depends on each inputs configuration as shown the following table Input Range Scaling mV 0 5 0 0001 5 0 0002 0 10 0 0002 Example To instruct the RQCM to output sensor 1 period and resistance the computer would send the following message Chr 255 Chr 254 Chr 1 Chr 1 Chr 3 Chr 3 Chr 0 Chr 0 Chr 248 The RQCM will then send one message every 50 milliseconds that it 12 bytes long and contains 6 bytes of data The first four bytes of data is sensor period and the next two bytes are sensor resistance Data logging is stopped by sending the following message Chr 255 Chr 254 Chr 1 Chr 1 Chr 3 Chr 0 Chr 0 Chr 0 Chr 25 1 3 Configure Data Acquisition Board Code 2 This instruction allows the computer to configure the input range and temperature units of the RQCM s Analog Input Temperature card The following table shows the byte configuration for this message COMPUTER INTERFACE 9
44. he lower half of the right figure shows the rear electrode also called contact electrode This configuration allows electrical contacts be made to both front and rear electrodes from the same side of the crystal WRAP AROUND EXIENDED ELECTRODE FRONT SIDE SIDE SENSING ELECTRODE CONTACT ELECTRODE Figure 6 Maxtek 1 Inch Diameter Crystals The figure below shows a Maxtek 1 diameter as seen from the front side CRYSTALS AND HOLDERS 3 1 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE MAXTEK 1 CRYSTAL AS SEEN FROM FRONT SIDE 3 2 CRYSTAL HOLDERS Figure 7 shows a Maxtek CHC 100 Crystal Holder without a crystal the crystal retainer and the retainer cover It has a cavity for 1 inch diameter crystal Inside the cavity there are two pogo pins providing connections to the crystal s front and rear electrodes Note the locations of the pogo pins These pins are internally connected to the BNC connector SMB Jack for CHT 100 and CHK 100 holders via an internal coaxial cable 3 2 CRYSTALS AND HOLDERS RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE INDEX PIN POGO PIN CONNECTS TO BNC CENTER POGO PIN 5 TO BNC HOUSING FEMALE BNC OR SMB JACK Figure 7 CHC 100 Crystal Holder 3 3 HOW TO INSTALL A CRYSTAL IN A CRYSTAL HOLDER 1 Identify the Front and Rear Sides of the crystal See Section 3 1 2 Clean amp Dry the Probe Holder cavity then insert the Crystal with the Front Side
45. imation the frequency error resulting from a given phase error 1s proportional to the bandwidth of the crystal The bandwidth of the crystal 1s proportional to the crystal s resistance A ten ohm crystal might typically have a bandwidth of 42 Hz while a one thousand ohm crystal will have a bandwidth of 4 200 Hz A five thousand ohm crystal will have a bandwidth of 21 000 Hz Since the frequency error for a given phase error 1s proportional to the bandwidth a phase error that would result in a 0 5 Hz frequency error in a ten ohm crystal will cause a 50 Hz error in a one thousand ohm crystal and 250 Hz error in a five thousand ohm crystal The second reason 15 that the effective phase error caused by a non zero net quadrature current 15 inversely proportional to the real current which 1s inversely proportional to the crystal resistance In other words the effective phase error 1s proportional to the crystal resistance For instance a net unbalance of 1 pfd leads to an effective phase error of 0 02 degrees for a ten ohm crystal but 1t leads to a 2 degree error for a one thousand ohm crystal and a 10 degree error for a five thousand ohm crystal Examples A ten ohm 5 crystal will have a Quality Factor of about 120 000 The bandwidth 1s equal to the crystal frequency divided by Q Thus the bandwidth of this crystal would be about 42 Hz To a first approximation near zero phase the frequency error per degree of phase error 15 given by
46. input or an output of the The RS 232 serial port can still be used with IEEE 488 installed However since both interfaces use the same input and output message buffers they should not be used at the same time This will result communication errors Figure 22 IEEE 488 Connector So End Or Identify o 6 DataValid 8 Not Accepted 9 Service Request COMPUTER INTERFACE RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE DATA I O 8 20 22 50 12 22 GND Table 2 IEEE 488 Pin Assignments 9 8 PROTOCOL All communications between the computer and the RQCM are in the form of messages with the format Two byte header FFh FEh Chr 255 Chr 254 The header indicates the beginning of a message One byte device address 1 to 32 The device address byte defines the bus address of the instrument that sent or should receive the message The device address will range from to 32 A message sent to a device address of zero will be received by all ROCMs except in the case of the IEEE 488 interface With this interface only the addressed device will receive the message One byte instruction code 0 to 6 Defines the code number of the message One byte message length 0 to 249 Indicates the number of data bytes contained in the message One byte checksum 0 to 255 The checksum byte 1s used for transmission error detection If the T
47. ivalent phase error is proportional to the crystal resistance a 1 pfd residual capacitance error will result 10 degree equivalent error for a sensing crystal with a resistance of 5 56 Polar Plot of Crystal Conductance IMAGINARY AXIS DIRECTION OF INCREASING FREQUENCY 250 SIEMENS 4KQ CRYSTAL WITH 1 pfd NET SHUNT CAPACITANCE EFFECTIVE PHASE ERROR DUE TO NON ZERO SHUNT CAPACITANCE REAL AXIS 5 x 100 SIEMENS 4KQ CRYSTAL WITH 0 pid NET SHUNT CAPACITANCE Figure 1 Equivalent Phase Error Due to Imperfect Capacitance Cancellation 1 4 GENERAL DESCRIPTION RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 1 3 SPECIFICATIONS 1 3 1 CRYSTAL MEASUREMENT Crystal measurement channels Frequency range Frequency resolution Mass resolution Capacitance compensation range Achievable capacitance cancellation Crystal resistance range Phase angle accuracy Phase angle stability Frequency error vs phase error and crystal Q Measurement update rate Operating temperature range Operating temperature range for stated stability Controls Indicators Crystal Drive Voltage open circuit Crystal Drive Source Impedance Crystal Power Crystal Face Isolation Q 100 000 0 087 ppm per degree Q 10 000 0 87 ppm per degree Q 1 000 8 7 ppm per degree Reset Switch Capacitance Adjustment Trimmer Course and Fine Green Lock LED Red Unlock LED Yellow Sweep Rate LED 1
48. ke water DATA ACQUISITION CARD OPTIONAL 10 3 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 11 CARD OPTIONAL The RQCM has one rear panel slot for the optional I O card The card has eight 8 level 0 to 5 volt DC inputs The inputs are pulled up to 5 volts internally through a 4 7 resistor and are set true assuming the input s True level 1s set to Low by shorting the input pins together There are eight 8 SPST relay outputs capable of handling 120 VA 2A max per relay These inputs and outputs can be used to control external instruments and peripheral devices such as pumps heaters valves instruments etc Figure 25 shows the connector pin configuration and Table 5 supplies pin signal assignments Refer to the online help of RQCM computer software for I O definition and programming instructions 000000000 6 900060 meo Figure 25 DB73P 1 Rear Panel Connector A CI 12 Input Return 381 22 Impu2Reun A Imput3 4 TER 92 np 15 _ 2 pT y 3 86 9 Iput8Retun 0 2 Table 5 DB37P I O Rear Panel Connector Pin Assignments 30 12 31 13 32 14 33 15 34 16 35 17 36 18 37 19 CARD OPTIONAL 11 1 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 12 TROUBLESHOOTING GUIDE This section is intended primarily as an aid understanding the RQCM operation and to help insolating
49. mand 9 Set RQCM Interface Address Code 8 This instruction allows the computer to set RQCM s interface address The RQCM s interface address allows for multiple instruments to share the same communications bus You can have multiple RQCM s on the same bus but each must have a unique interface address so the computer can communicate with each one individually The interface address can range from 1 to 32 RQCM s are shipped with the interface address set to one For example To set the RQCM s interface address to 2 the computer would send Chr 255 Chr 254 Chr 1 Chr 8 Chr 1 Chr 2 Chr 244 If using the IEEE interface then the computer must also send a device clear before the new interface address takes affect The new interface address will take affect immediately when using either RS 232 or RS 485 COMPUTER INTERFACE 9 9 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 10 DATA ACQUISITION CARD OPTIONAL The RQCM has one rear panel slot for the optional Data Acquisition Card The card has three 3 temperature inputs to accommodate an RTD thermocouple or thermistor There are also five 5 scalable analog inputs for measurement and logging of DC voltages Except for the thermocouple input which has 1ts own connector all other temperature inputs and analog inputs are on a D SUB 25 pin male connector Figure 23 shows the connector pin configuration and Table 3 shows the pin signal assignments Refer to the
50. nnect the other end of the cable to the computer serial port If you have the IEEE 488 communication option install the proper cable Refer to Section 9 1 to install setup and run the software Connect the crystal holder with a crystal installed to the SMB connector labeled Crystal by means of the 12 inch SMB coaxial cable Observe the AC voltage setting on the rear panel Make sure it is set for your local line voltage Plug one end of the power cord to a power outlet and plug the other end into the rear of the Refer to Figure 3 and Figure 5 for complete system connections Switch the front panel power switch to on Start the Application program Note that you may have to set the RQCM address and select the correct COMM port in the Setup Menu in order for the RQCM to communicate with your PC Click on the View Status button to bring up the Status Screen On the RQCM front panel the green Lock LED should be on On the computer Status screen the frequency should indicate the correct crystal frequency and the resistance should indicate something between 5 and 15 for an uncoated polished crystal in air 2 4 UNDERSTANDING AND SETTING UP A CRYSTAL MEASUREMENT CHANNEL RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE Check the capacitance cancellation by pressing and holding the Reset switch The green Lock LED should light Keeping the Reset switch pressed adjust the fine capacitance tr mmer clockwise b
51. on etc 1 1 FEATURES 1 1 1 VERY WIDE FREQUENCY RANGE The RQCM supports a wide frequency range from 3 8 to over 6 MHz It will support both 5 and 6 crystals and with a low limit of 3 8 MHz 1t will support 1 2 MHz of frequency shift on a SMHz crystal A frequency range of 5 1 to over 10 MHz 15 also available 1 1 2 SUPPORT FOR VERY LOW HIGHLY DAMPED CRYSTALS The RQCM will reliably lock to crystals with resistance of 5 KQ or less In most cases it will maintain lock up to a resistance of 10 KQ or more It will support crystal oscillation in highly viscous solutions of more than 88 glycol 1n water GENERAL DESCRIPTION 1 1 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 1 1 3 DIRECT REAL TIME MEASUREMENTS OF CRYSTAL FREQUENCY MASS AND RESISTANCE The RQCM accurately measures crystal frequency mass and resistance The software uses this data to derive various physical parameters of the deposited film or media at the surface of the crystal 1 1 4 MULTIPLE CRYSTAL MEASUREMENT CHANNELS The RQCM can be configured for up to three crystal measurement channels All channels are measured simultaneously 1 15 ELECTRODE CAPACITANCE CANCELLATION The total quartz crystal impedance includes a shunt capacitance due to the capacitance of the crystal electrodes cable and holder parallel with the series resonant arm The total current through the crystal is the sum of the current through the shunt capacitance plus the current
52. online help included in the ROCM software for instructions on setting up and programming these inputs 13 000000200000 4 0 O0 O 5 o0 6 60 0x0 6 Figure 23 DB25P Data Acquisition Rear Panel Connector Table 3 DB25P Data Acquision Rear Panel Connector Pin Assignments 10 1 VOLTAGE INPUTS Each of the five 5 inputs can be configured as 0 to 5V 0 to 10V 5 or 10V The unipolar positive inputs can be connected as unipolar negative inputs The resolution of the data is dependent on the range selection as shown in the table below Configuration 0 to 10V d Table 4 Input Voltage Resolution The voltage input pairs are labeled as Input and Common The Input pin is the positive input and the Common pin 15 the negative input The common mode range 15 200V so the Common pin can be used to read unipolar negative voltages with the input pin as common Each input also has a Shield pin for shielded cable termination Shielded twisted pair cable 15 recommended for connections longer than a foot DATA ACQUISITION CARD OPTIONAL 10 1 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 10 2 TEMPERATURE INPUTS Three temperature inputs are included to support the three most commonly used temperature sensors thermistor Resistance Temperature Detector RTD or type T copper constantan thermocouple 10 2 1 THERMISTOR INPUT The Thermistor Input 15 designed to use an Omega 10 25 C Precision Interchangeabl
53. onnector Table 1 D9 Rear Panel RS 232 RS 485 Connector Pin Assignments 9 6 RS 485 SERIAL INTERFACE The optional RS 485 serial interface of the RQCM allows connection of up to 32 separate devices equipped with RS 485 The RS 485 serial interface is also ideal electrically noisy environments and applications where long cables are required The RS 485 of the RQCM is the same D9P connector on the rear panel used for RS 232 The pin layout is shown in Figure 21 and Table 111 the pin signal assignments including a 9 2 COMPUTER INTERFACE RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE definition of whether the signal 15 an input or an output of the RQCM The RQCM s RS 485 port is automatically set up to operate with the following specifications 19200 Baud 8 Bit data No Parity 1 Stop bit 9 7 IEEE 488 PARALLEL INTERFACE The optional IEEE 488 interface provides with the ability to communicate with computers and other devices over a standard IEEE 488 interface bus The IEEE 488 interface also known as GPIB or HPIB provides an eight bit parallel asynchronous interface between up to 15 individual devices on the same bus This means that one computer equipped with an IEEE 488 interface card can communicate with up to 14 RQCMs or other devices The pin layout of the IEEE 488 port 1s shown in Figure 22 and Table 2 lists the pin signal assignments including a definition of whether the signal 1s an
54. pe T Thermocouple has a range of 0 to 371 C The use of a thermocouple is recommended in oxidizing reducing inert or vacuum atmosphere within its temperature range 10 2 DATA ACQUISITION CARD OPTIONAL RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE m CONST Figure 24 Rear Panel Type T Thermocouple Connector 10 3 GROUNDING CONSIDERATION Proper grounding and shield termination is mandatory for accurate measurements 10 3 1 VOLTAGE MEASUREMENT GROUNDING If the voltage to be measured 1s returned to earth ground within the common mode voltage range at its source neither the Input nor the Common lead should be grounded at the voltage measurement point since the RQCM will return to earth ground through its power cord The shield for the input leads must only be terminated at the Data Acquisition Card connector If the voltage to be measured 15 isolated from earth ground the shield or its drain wire should be connected to the common side of the voltage to be measured at the voltage source as well as at the shield terminal on the RQCM Data Acquisition Card 10 3 2 TEMPERATURE MEASUREMENT GROUNDING All three temperature sensors must be of the isolated or ungrounded type Sensor lead wire shields should be terminated at the RQCM Data Acquisition Card connector only The measured device should be connected to earth ground Exposed junction probes should not be used to measure the temperature in a conductive media li
55. tek cable and crystal holder Ifa Maxtek cable and crystal holder 15 being used then no initial adjustments should be needed During normal operation with a crystal installed and connected to the oscillator the green Lock LED will be on and the frequency output will reflect the crystal resonance The red Unlock LED will be off If the Unlock LED 15 on the Sweep Rate LED should slowly flash Continuous sweeping of the frequency range indicates that the 5 resonant frequency is outside of the PLO s frequency range or the crystal s conductance is below the conductance threshold No flashing of the Sweep Rate LED when the Unlock LED 15 on can mean one of two things First if the VCO frequency is sitting at its low limit it means the electrode capacitance 15 over compensated Second in some cases even though the crystal conductance has fallen below the threshold necessary to indicate lock the internal signals are still sufficient to keep the VCO locked to the crystal In that case the PLO really 15 locked and the VCO frequency will be sitting at the crystal frequency somewhere between its minimum and maximum frequencies If the VCO frequency is sitting at its low limit press and hold the Reset switch and adjust the fine capacitance trimmer a few degrees clockwise not more than ten until the Sweep LED begins to flash 24 CHECKOUT Connect the DB9S computer cable to the RS 232 RS 485 port located on the rear of the RQCM Co
56. th 888023 Adapter BNC Male to SMB Jack 803081 803312 Capacitance Tuning Tool Refer to Maxtek Price List for more accessories and other products 1 5 OPTIONAL CARDS Part Number 603208 Crystal Measurement Card 603209 Data Acquisition Card 603210 Passive Card GENERAL DESCRIPTION 1 7 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 2 UNDERSTANDING AND SETTING UP A CRYSTAL MEASUREMENT CHANNEL The RQCM can have up to three independent crystal measurement channels Each channel has a crystal input three status LED s fine and course capacitance adjustments a reset switch and a crystal face connection Refer to Figure 2 2 1 FRONT PANEL DESCRIPTION 2 1 1 LOCK INDICATOR The green Lock LED is on when the frequency is locked on a 5 resonant frequency 2 1 2 UNLOCK INDICATOR The Red Unlock LED will be on whenever the frequency 15 not locked on a crystal 2 1 3 SWEEP RATE INDICATOR The Yellow Sweep Rate LED flashes each time the frequency ramp 15 reset to its low starting point In normal operation the sweep light will only flash while adjusting the capacitance compensation The Sweep LED will not light when locked on a crystal 2 1 4 RESET SWITCH The Reset switch should be pressed while adjusting the capacitance compensation This switch forces the VCO to its lowest frequency independently of the Integrator output The Reset switch also forces the Lock LED on thus turning off the quadrature curr
57. through the series resonant arm The physical motion of the crystal is reflected in the values of the L R and C in the series arm of the crystal only and therefore we want to subtract out or otherwise cancel the current through the shunt electrode capacitance The Crystal Measurement Card includes a method of canceling the electrode capacitance insuring that the measured crystal current does not include the current through the electrode capacitance and therefore is essentially the current through the series resonant arm of the crystal only 1 1 6 AUTOLOCK When the PLO loses lock the VCO Voltage Controlled Oscillator is ramped up to the maximum frequency at which time it 1s automatically reset to the minimum frequency and a new scan 15 initiated To insure that the VCO ramps up in frequency a small amount of quadrature current 15 injected into the current to voltage buffer whenever the PLO 15 unlocked This current is equivalent to a shunt capacitance of about 1 5 pfd As soon as lock 15 detected the quadrature current is turned off 1 1 7 CRYSTAL FACE ISOLATION The Crystal face is galvanically transformer isolated from earth ground The Crystal Face connection allows the crystal face to be easily connected to an external voltage or current source such as a potentiostat 1 1 8 FULLY INTERGATED COMPUTER SOFTWARE Computer software is included with each RQCM allowing the user to set up graph and log frequency and resistance of the cr
58. ults from previous experiments The QCM portion of this system accurately measures crystal frequency and crystal resistance for up to three crystals simultaneously The software uses this data to derive various physical parameters of the deposited film and or the liquid or gas environment at the surface of the crystal The heart of the system 1s a high performance phase lock oscillator PLO circuit that provides superior measurement stability over a wide frequency range 3 8 to 6 06 MHz or 5 1 to 10 MHz The circuit also incorporates adjustable crystal capacitance cancellation reducing error caused by the parasitic capacitance of the crystal cable and fixture Capacitance cancellation 1s essential for accurate measurements of lossy soft films Data collection from external sources 1s accomplished with an optional Data Acquisition Card which provides three temperature inputs RTD Thermocouple and Thermistor as well as five scalable analog inputs As for example the user can combine the potential and current outputs of a potentiostat with the mass frequency and crystal resistance data of the QCM Control of external instruments and peripheral devices 15 accomplished with an optional input output card Each remote I O card provides eight remote inputs and eight relay outputs The functions of the inputs and outputs are defined the RQCM s software with some typical uses including the control of pumps heaters valves instrument initiati
59. ve environment to avoid electrical short between electrodes The electrodes should be designed so the rear electrode and the electrodes contacts can be sealed Only the front electrode should be exposed The connecting cable must be coaxial all the way from SMB on the RQCM on up to the crystal The shield of the coaxial must connect to the front electrode and the center conductor must connect to the rear electrode of the crystal In addition the coaxial cable must be free of kinks knots etc to avoid unbalanced capacitance cable Note that a one foot of well balance RG174A U coaxial cable has approximately 29 picofarads The total capacitance of the crystal the crystal holder and the cable must be within the RQCM s capacitance compensation limits between 40 and 200 pfd CRYSTALS AND HOLDERS 3 5 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 4 ELECTRICAL DESCRIPTION OF THE QUARTZ CRYSTAL Figure 9 shows the equivalent circuit of a quartz crystal The circuit has two branches The motional branch which contains L 15 the branch that 15 modified by mass and viscous loading of the crystal The shunt branch which contains the lone Cs element represents the shunt capacitance of the crystal electrodes and any cable and fixture capacitance Cs Figure 9 Crystal Equivalent Circuit Because a crystal s impedance is minimum at resonance it is convenient to characterize a crystal in
60. y about 5 degrees The yellow Sweep LED should flash Back tr mmer counterclockwise to the point where Sweep LED just stops flashing The capacitance cancellation should be checked and readjusted every time the environment of the crystal and holder is changed I e if the crystal and holder are moved from air to liquid or liquid to air the capacitance cancellation should be checked and readjusted Remove the crystal The red Unlock LED should light The green Lock LED should go off The Sweep Rate LED should not flash If the Sweep Rate LED flashes the capacitance is under compensated Reinstall the crystal in the holder and repeat the process until it 1s perfectly compensated Sweep LED not flashing when the crystal 15 removed Refer to Section 5 for more details on adjusting the capacitance cancellation Record the frequency and resistance using an uncoated 5 MHz polished crystal in air after adjusting for the capacitance If you are using Maxtek 1 Polished 5 MHz Gold Electrode Crystal the frequency should be between 4 976 to 5 020 MHz and the resistance should be between 5 to 15 ohms Next submerge the crystal holder into room temperature water and adjust for capacitance The frequency change should be about 650 Hz and the resistance change should be about 364 ohms from the readings in air UNDERSTANDING AND SETTING UP A CRYSTAL MEASUREMENT CHANNEL 2 5 RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE CHANNEL 1 RESET
61. ystals from a computer It also allows the setup graphing and logging of temperature and analog data if the hardware is installed 1 2 GENERAL DESCRIPTION RQCM RESEARCH QUARTZ CRYSTAL MICROBALANCE 1 1 9 INPUTS AND OUTPUTS CAPABILITY As an option the RQCM can be outfitted with an I O Card This card provides eight remote discrete inputs and eight relay outputs These I O s can be used to monitor or control external instruments and peripheral devices 1 1 10 DATA ACQUISITION CAPABILITY To support the simultaneous logging and display of additional analog information such as voltage current or temperature the RQCM can be outfitted with an optional Data Acquisition Card This card supports three types of temperature sensors RTD Thermocouple and Thermistor as well as five scalable analog inputs 1 2 CHARACTERIZING THE CRYSTAL MEASUREMENT 1 2 1 FREQUENCY ERRORS The first thing we want to know regarding the performance of the crystal measurement is What is the magnitude of the frequency error we can expect from the crystal measurement portion of the RQCM In any oscillator and sensing crystal system the error in the frequency measurement is a function of both the oscillator and the sensing crystal The same is true for phase locked loops Any phase error will introduce a frequency error and this frequency error will be inversely proportional to the sensing crystal s Q These errors are over and above any change in
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