CT2 Counter Module User Manual
Contents
1. in photon counting detectors including optical transmission and reflection losses in the photomultiplier window are shown in Figure 1 Figure 1 30 20 oO Quantum efficiency 0 100 300 500 700 900 Wavelength nm Photoelectrons emitted by the photocathode are accelerated and focused by electric fields onto the first dynode of the electron multiplier section of the photomultiplier On impact each photoelectron liberates a number of secondary electrons which are in turn accelerated and focused onto the second dynode The process is repeated at each subsequent dynode and the secondary electrons from the tenth and last dynode are collected at the anode Resultant charge pulses from the photomultiplier will vary in magnitude due to the statistical nature of the gain process but so long as they exceed the preset threshold of the discriminator each will be counted as one pulse Only small pulses resulting from single electrons originating from intermediate dynodes will fall below the threshold and be rejected 12 The voltage applied to the photomultiplier tube in the Detector is normally factory preset to provide the optimum gain for photon counting At this operating point on the signal counts voltage plateau characteristic the slope is typically 0 2 per volt or less 1 2 Signal to Noise The photoelectric effect is a quantum mechanical process subject to fluctua2. this the statistical uncertainty associated with the subtraction process becomes excessive In background subtraction the signal count rate is deduced as the difference between the measured rates of s b for signal and background and b for background alone It should therefore be noted that the signal to noise ratio for the deduced signal rate will be s s 2b and not s s At high count rates dynamic range is limited by electronic dead time effects caused by pulse pile up Pulses that arrive whilst the discriminator is busy are ignored Correction for dead time is automatically applied in the form N n 1 nt where N is the corrected count rate n is the measured count rate and T is the count rate correction factor 15 APPENDIX A CT2 Interface Characteristics Absolute maximum ratings T TTT Sare T ee SO User out 1 current out 1 current User out 2 load current Output sinking e 0 01V amb 25C Ta S O A DC characteristics Ta 25 C Supply 4 75V to 5 5V al a RO TTL erae TE msme H G G H HH S e E H IS E E E Output low volts max Output sinking 20mA Output high volts min Output sourcing 80u A i 4 S MERGE sourcing 12uA 4 E ase ll Pa wn Resa Owe HH H ne T HT 16 CT2 Hirose connector Box lid user out 2 user out 1 open drain trig in 5V out View looking into socket 17 APPENDIX B ENVIRONMENTAL CONDITIONS TEMPERATURE operating 5 to 5
3. 5 C VIBRATION SINUSOIDAL non operating 10 to 500 Hz for 10 cycles in each axis at a peak amplitude of 2g 1 octave min VIBRATION RANDOM non operating 20 Hz at 0 02 g Hz to 50 Hz at 0 02 g Hz falling to 500 Hz at 0 001 g Hz HUMIDITY non condensing 30 C 93 PRESSURE operating Pressure reductions from 100 kPa 1 bar to 68 kPa 0 68 bar 18 APPENDIX C OUTLINE DRAWING 19 APPENDIX D The EM6 ActiveX control This is the documentation for the EM6 ActiveX control It describes the function and parameters of the Methods properties and events in the control Several examples accompany this documentation to provide a headstart in development Currently examples exist for Visual Basic Labview Excel and Delphi The examples are intended as a guide to programming with the EM6 ActiveX control and not as complete solutions The following sample method describes the correct sequence for using the EM6 ActiveX control with appropriate examples for each step 1 First open the COM port object Open 1 2 Then setup the EM6 device object Continuous false object Triggered false object OutputSignal false object OutputVoltage true object Period 10 object ReadingCount 100 3 Call the Start method and handle the events generated object Start 4 Finish by closing the COM port object Close Remarks Often the comport will be opened for the entire duration
4. CT2 Counter Module User Manual Detector Modules Group Electron Tubes Limited Bury Street Ruislip HA4 7TA UK December 2002 CONTENTS PRECAUTIONS INSTALLATION START UP SOFTWARE PROGRAMMING TROUBLESHOOTING BACKGROUND INFORMATION APPENDIX A Interface Characteristics APPENDIX B Environmental Conditions APPENDIX C Outline Drawing APPENDIX D Active X Component 1 PRECAUTIONS SUPPLY VOLTAGE Ensure the 5V supply voltage does not exceed 5 25V Exceeding 6 0V on the Module may result in permanent damage to the unit and it will have to be returned to the factory for repair See Appendix A MAINTENANCE There are no user maintainable components in the Module Modules should be returned to Electron Tubes for repair ENVIRONMENT The Module should not be exposed to levels outside those specified in Appendix B 2 INSTALLATION The following instructions will enable users to utilise the software provided to operate the CT2 Module such that results can be taken immediately and the hardware setup can be checked 1 System Requirements PC operating under Microsoft Windows 98 2000 or XP Mouse or tablet VGA resolution monitor or higher CD ROM drive 5V Power Supply Interfaces See Appendix A for details Connect Detector signal to input BNC on CT2 Connect the 9 way connector to the serial port on the computer noting which port is used Connect a 5V Power Supply to the Power Connector on th
5. ciency and hence of responsivity is shown in Figure 2 13 1 0 0 8 0 6 0 4 0 2 0 Temperature Coefficient C 0 2 Figure 2 Bialkali RbCs 20 300 1 4 Background 400 500 600 700 Wavelength nm 800 900 Background or dark count is the unwanted signal produced by the photomultiplier tube in the absence of light stimulation Dark counts in Photon Counting Detectors are a function of photocathode type and temperature as shown in Figure 3 Figure 3 5 10 4 10 R 10 Cc 3 S20 RbCs oO 2 x 10 Bialkali LS O 1 10 0 10 60 40 20 0 20 40 60 Temperature C Dynamic Range Figure 4 2 2 2 G O 5 B J O a oS Bialkali With dark count subtraction 10 10 Incident Light Power W at 400 nm and 20 C 14 10 10 Typical dynamic range is shown in Figure 4 Over the majority of their useful operating range the responsivity of Photon Counting Detectors is linear and will produce an output count rate which is proportional to input light power At low count rates the effect of background or dark counts becomes significant Some improvement can be achieved by cooling or at least preventing the package from being heated by other apparatus Dark count subtraction can be used down to the point at which signal becomes less than about 1 10 of background Beyond
6. e Control 3 START UP SOFTWARE Software has been provided with Module to allow for immediate use of the product without the need for writing new software programmes However custom user programmes may be required and Section 4 PROGRAMMING defines the necessary interface protocol for users to follow The software provided with the Module can be operated by carrying out the following simple steps Before using the software the Module must be connected as stated in Section 2 INSTALLATION If the Control box is not already displayed select it from the Tool bar in the Window box Control Window In the Control Window set up the following 1 Readings Select the total number of readings you wish to take 32000 max Ds Period Select the period of the reading 10ms to 300s By clicking on the box that states the units of the period setting the user can toggle between ms 10 2500 amp s 1 300 When s 1 300 is used the software reads counts from the hardware every 1s and then accumulates the results until the desired period is achieved When ms 10 2500 is used the software reads counts from the hardware dependent on the period set 3 Trigger Mode Select the trigger mode as either Off Fixed or Continuous 4 User outputs Select the Output Signal as on or off This will then control the appropriate external output line switching it between logic 1 and 0 to permit control
7. e Module If used make the appropriate connections to the User out 1 pin 1 amp 2 pin 6 and the Trig in pin 2 Switch on the computer and 5V Power Supply Software Installation Insert the EM6 Counter Timer Software compact disc into the CD ROM drive of your computer Note CT2 installation set up starts automatically on most computers If it doesn t on your computer click the START button and then click RUN In the RUN dialog box type d setup where d is the letter of your CD ROM drive Software Operation On entering the program a product request screen shall be displayed CT2 needs to be selected here Select Product X Please select a device from the list below Product IV Don t ask this again Select Before starting counting the correct communications port must be selected Dependant on which communications port the Module has been plugged into on the computer go into File and then New and select the appropriate port This will then be saved as the default setting If an incorrect port is selected an error box will be displayed and the user should select another port gt a New E COMI E CoM f CUMS f CUMS The Module is now ready to be used By selecting Window amp Show Control Window the control window will be displayed and allow the counter to be started based on the settings in this window Detailed setting up instructions can be found in Section 3 Start up Softwar
8. eadings where each reading is timed over P 10ms The readings are terminated by sending the Stop command CR or other command C L Allows continuous readings Readings are initiated where each The VA Valid message first reading is timed over P 10ms whenever the External Trigger Then when initiated as pin is 1 and inhibits readings whenever the External Trigger pin described the readings are sent to is 0 the PC as for the S and C Sending the Stop command CR or other command terminates commands above this mode of operation E Allows R readings where each reading is timed over P 10ms Each reading is initiated at the positive edge of the External Trigger pin This may be repeated any number of times Sending the Stop command CR or other command terminates this mode of operation M Starts R readings where each reading is timed over P 10ms No readings are sent to the PC The readings are sequentially stored in the non volatile but when all of the readings have EEPROM along with the number of readings taken overwriting been taken the MF message is the currently stored readings Overflowed readings are also sent to the PC stored If R is greater than 126 only 126 readings are taken and stored Sends the readings held in the non volatile memory to the PC The readings held in the non These readings remain in the non volatile memory until volatile memory overwritten by the consequences of an M command Cancels the curre
9. essing OnBufferOverrun Occurs when the FIFO buffer attempts to grow to a size greater than the one specified in the BufferSize property 21
10. ge Return Line Feed pair CR LF except for the Stop command which is just a CR All Command acknowledgments and all results sent to the PC are not terminated with a CR LF pair All commands will stop any reading in progress or stop any EEPROM memory transmission to the PC and then perform the specified action Generally a command will cause a transmission of a message or transmission of readings to the PC as indicated below The commands are case sensitive Also initial characters other than S C L E M B R P T O D and V will be ignored If the character following a correct initial character is incorrect or a character pair other than a CR LF is received when a CR LF character pair is expected a BC Bad Command message is sent to the PC VI AST Start Message is sent to the PC at power up and whenever a Reset occurs Command Action CCC Returns to PC Starts R readings where each reading is timed over P 10ms At the end of each reading the reading is sent to the PC in binary form as 4 bytes with the most significant byte sent first If the count becomes greater than 67 108 863 during a reading that reading is terminated immediately and an error reading is sent to the PC The software then continues with the next reading An error reading is distinguished by having the most significant bit of the first byte as a 1 otherwise its a 0 Thus a valid reading has a maximum of 31 bits Starts continuous r
11. nt set of readings The SP Stopped message If in the Continuous External Trigger mode it is cancelled R followed bya Sets the Number of Readings setting R to the byte value of the The VA Valid message character character following R A Ois seen as 1 Numbers greater than 255 cause a BC message to be sent to the PC The default Number of Readings is 1 P followed bya Sets the Periods setting P to the number following P The VA Valid message character A Ois changed to 1 Numbers greater than 255 cause a BC message to be sent to the PC The default Periods is 10 Command Action CCC Returns to PC T followed by a number 0 to 500 ie 1 to 3 digits O followed by a character V followed by two characters Sets the Linearity setting T to the number following T A U turns off the linearity transformation Numbers greater than 500 cause a BC message to be sent to the PC On power up the previous Linearity setting is reinstated The initial Linearity setting is factory set during manufacture Turns on the Output Signal 1 when the character following the O has a byte value of 1 or turns the Output Signal 1 off the when it has a byte value of 0 Byte values greater than cause a BC message to be sent to the PC The default value is off Turns off the Output Signal 2 when both of the characters following the V have byte values of zero or turns on the Output Signal 2 if either one of the characte
12. of external apparatus such as a shutter mechanism See Appendix A 5 Start Stop Selecting Start Stop will either Start or Stop the software On selecting Start the software shall function depending on the selection made in the Control Window Electron Tubes EM6 Counter Timer Software 16 l LRS 2 3 4 56 7 8 9 10 11 12 13 14 15 16 17 18 19 42321067 42325136 42325136 42331302 42331302 42341528 42341528 42347751 42347751 42360143 42360143 42334605 42334605 42354846 42354846 42344599 42344599 42355062 _ 42355062 42335591 42335591 42303669 42303669 42311807 42311807 42333330 42333330 1 42326255 42326255 EM6 Counter Timer Software Window The following facilities are available from the Main Window both as drop down menus and as items on the toolbar File New Open Save Save as Print Graph Only Data Only Graph amp Data Note Exit Edit Change product Enables the communication lines to be set as stated in Section 2 Installation Open enables the user to select a previous set of results for analysis Save enables the user to save a set of results Enables the user to change the save file name Print Graph Only prints out the graph of results Print Data Only prints out the table of results Prints out both the data and graph of results By clicking on the graph on the screen titles can be set for the graph to appear on the printed copy Exit exi
13. of the program Properties BufferInUse Read Gets the number of readings currently in the buffer that are only awaiting processing Buffersize Gets or sets the number of slots available to the software FIFO buffer Continuous Gets or sets the continuous mode of data acquisition Setting this property to TRUE causes data acquisition to be continuous Setting this value to false causes data acquisition to stop after the number of readings specified in the ReadingCount property Output Signal Gets or sets the state of the output signal Setting this property to TRUE causes the output signal to be switched on Output Voltage Gets or sets the state of the output voltage Setting this property to TRUE causes the output voltage to be switched on Period Gets or sets the counter timer timeout period ReadingCount Gets or sets the number of readings to be taken in non continuous acquisition mode Triggered Gets or sets the triggered mode of data acquisition Setting this property to TRUE enables 20 Methods Close Closes the COM port used by the EM6 ActiveX control Open Opens a COM port for use by the EM6 ActiveX control Start Begins counting Stop Ends counting Close Closes the COM port used by the EM6 ActiveX control Open Opens a COM port for use by the EM6 ActiveX control Start Begins counting Events Result Occurs when a new reading is available for proc
14. rs has a byte value that is not zero The default value is off The VA Valid message The VA Valid message The VA Valid message D T Turns on the Output Signal 2 The VA Valid message 10 5 TROUBLE SHOOTING 1 No Counts Check all connections have been made correctly Check the 5V Power Supply is on and correctly set Check the Detector is funtioning properly Count Overflow or Very High Count Rates Check Detector optical connection is light tight Software will not Install Check computer running Windows 98 2000 or XP No Readings can be taken Check count mode not selected to external trigger or trigger not available 11 6 BACKGROUND INFORMATION 1 Operating Principles Many photodetector packages use photomultiplier tubes operating in the photon counting mode The following paragraphs summarize the salient features of this technique and provide typical performance data for these packages 1 1 Photon Counting The following section details the background information for Photon Counting the primary role for the CT2 Module Photon counting is the most sensitive method for measuring weak or short lived light emissions Each photon incident on the photocathode has a wavelength dependent probability of releasing a photoelectron This probability is known as the quantum efficiency QE and is normally expressed as a percentage Typical spectral response characteristics for the photocathodes used
15. tions described by Poisson statistics A steady light source generating m photoelectons per second for a period of t seconds 1 will produce an average of mt photoelectrons with a standard deviation of mO Hence signal to noise ratio is given by mt mt mt In photon counting there is negligible additional noise generated in the gain process or in the amplifier discriminator hence this expression is also valid for the complete Detector It should be noted that the signal to noise ratio depends on the number of counts hence for low count rates an increased measurement period will be advantageous 1 3 Responsivity The responsivity of the Detector is the output count rate less dark counts for a given light power incident on the photomultiplier input window Responsivity QE f IE h c where QEo is the quantum efficiency of the photocathode at wavelength A h is Planck s Constant 6 626 10 J s c is the speed of light 3 10 ms and f is the collection efficiency of the first dynode typically 0 95 for the standard range of photomultipliers used in photon counting Hence for 400 nm light a package with a bialkali photocathode photomultiplier with a typical QE of 0 25 has a responsivity of 4 78 10 counts W 1 fW of 400 nm light incident on the photomultiplier input window will therefore produce a mean output count rate of 478 s excluding dark counts The temperature coefficient of quantum effi
16. ts the program This enables the hardware type to be changed Linearity Correction This enables the count rate correction value to be Copy Select All Help Technical support About inserted to ensure linearity is maintained for the full dynamic range of the photon counting product being used See Section 6 BACKGROUND INFORMATION for more information Copies highlighted data to the clipboard to enable it to be pasted into other software applications such as a spreadsheet or word processor Selects and highlights all of the data in the table This takes you to the Electron Tubes web site where a list of technical support contacts are available This states the software version being used 4 PROGRAMMING The following table lists the commands necessary to operate the Module when an independent software application is to be written In addition an ActiveX control driver is provided on the installation CD together with example programmes for use with Excel Lab View Visual Basic and Delphi Details of this module are shown in Appendix D Command Description L D i IV The readings can only be initiated and settings can only be set by sending commands from the PC The results from a Start command are sent to the PC as four binary bytes Commands are acknowledged by sending a two character ASCII message to the PC All commands from the PC consist of ASCII characters and must be terminated with a Carria
Download Pdf Manuals
Related Search