User Manual
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1. It is not necessary to reduce this further provided the margin between the test result and the limit is greater than this noise e g noise 1mm limit 10mm test result 6mm In other cases additional efforts should be made to reduce the noise increase the metal shield around the test set up make sure the operator is touching the shield during the test or choose a different test location If a function generator input is used and the frequency is different to that of the environment e g input 50Hz environment 60Hz the result on the ECG may show some beating with the residual noise from the environment This beating should be at a frequency equal to the difference in frequencies e g 10Hz and not greater in amplitude than the residual noise when no input is applied If the set frequency is nominally the same as the environment e g input 50Hz environment 50Hz the beating may be extremely slow because of slight differences in frequency e g environment noise 50 00Hz function generator 50 10Hz would result in beating with 10s period The beating above is not of concern provided the margin to the limit is sufficient 3 Battery life CAUTION The internal 300mV is sourced from a SR44 1 5V alkaline battery By calculation this battery should last in excess of ER o 100hrs which far exceeds the expected demands during E testing However if the user accidentally leaves the DC offset os is switch on the battery can be d2. The WhaleTeg CMRR 2 0 is supplied with two breakout box to suit different standards IEC 60601 2 25 2011 formerly IEC 60601 2 51 IEC 60601 2 47 2012 and IEC 60601 2 27 requires 9 leads RA RL LL V1 to V6 to be shorted to inner box with only RL N and Imbalance with DC having the impedance of Technical Innovation from MEDTEQ RA R LA L LENF RL N CMRR Imbalance with DC i an om y CMRR ECG Breakout Box for IEC60601 2 25 IEC60601 2 27 51kQ 47nF To implement this a special WHALETEQ JEC60601 2 47 1EC60601 2 51 breakout box is used which shorts 9 terminals to the inner shield except RL N and Imbalance with Vi V v3 v4 v5 ve DC terminal The effective circuit is 51kQ CM voltage 10Vrms o DC offset Imbalance terminal 100pF 100pF 20Vrms 47nF db 9 terminals RA LA LL V1 V6 o 51k0 AA C RUN 47nF The test circuit in IEC 60601 2 47 2001 and a ANSI AAMI EC 13 is the same except that all lead electrodes have the 51k 47nF except one id esa sane OS which is directly connected to the inner shield PRJ Re wa ECG Breakout Box A General purpose and CMRR masa for AAMI ANSI EC13 no DC This has the effective circuit CM voltage 10Vrms DC Imbalance 100pF Each lead has 100pF 51k0 47nF 20Vrms HO Doo o Other terminals dn a RA LA LL RL V1 V6 O Imbalance no DC aT WHALETEQ Common Mode Rejection Ratio Tester User Manual 3 S
3. The test in the standard simulates 10Vrms with an imbalance of 51kQ 47nF and allows an indication equivalent to 0 35mVrms 1mVpp This requires ECG equipment to have a relatively large CMRR of 89dB In practice ECG equipment handles this large CMRR in five ways Intentional capacitance between the patient circuit and earth small enough not to cause leakage current problems but large enough to load the source and reduce the voltage by 50 or more This is the reason for the 100pF in the test circuit Right leg drive this is similar to noise reducing headphones where the noise is sensed on measurement leads e g RA LA LL inverted and then returned via the RL N lead electrode Also referred to a noise cancellation Patient isolation barrier which reduces the impact of the common mode voltage High CMRR input op amps to handle the residual common mode voltage Finally filtering can be used to remove residual common mode mains noise 1 This value can be calculated from 20 logio 10V 0 35mV aT WHALETEQ Common Mode Rejection Ratio Tester User Manual While filtering is often used in practice it is reasonable to confirm that the hardware features can provide sufficient CMRR without filtering This ensures that distortion of the signal will not occur For this reason mains notch filtering ac filter must be turned off for the test even if it requires special software to do so This is one point where t
4. sit on an earthed plane the stray capacitance can be enough to provide additional loading and reduce the actual common mode voltage This stray capacitance is highly variable and thus can impact the test For conservative tests the cable should be supported off the earth plane but remain above the earth plane in order to minimize noise For IEC 60601 2 25 2011 IEC 60601 2 27 and IEC 60601 2 51 the test requires a 20Vrms source This can be sourced from the mains supply but for those wishing to test at various frequencies and have good control over the applied voltage use of a function generator is more convenient A function generator is usually limited to 7 1Vrms 20Vpp To assist with this WhaleTeq s equipment has a small transformer built into the equipment which allows the voltage to be stepped up to 20Vrms The applied voltage can then verified at the Input and GND terminals Common mode rejection is also dependent on impedance imbalance For this reason the test also introduces an imbalance of 51kQ 47nF in one lead only Experience from tests indicates that without this imbalance there is usually no visible indication on the ECG but with the imbalance readings typically range between 3 7mm 0 3 0 7mVpp This suggests that the value of imbalance impedance is critical for the tests Although the diagram in the standard shows all switches open for the purpose of the test all switches should be closed except the lead bein
5. aT WHALETEQ Common Mode Rejection Ratio Tester User Manual WHALETEQ Common Mode Rejection Ratio Tester CMRR 2 0 User Manual Common Mode Rejection Ratio Test Unit 2 0 For IEC60601 2 25 2 27 7 2 47 2 51 ANSVAAMI EC11 EC13 E FE ge V1 V2 V3 V4 V5 V6 o ss A ID rr AT me Revision 2015 08 14 aY WHALETEQ Common Mode Rejection Ratio Tester User Manual Contents E INtROQUENO Ns wc oes cit css EOE T E NEE 2 Z DeSCrpPLON nr 3 Za CMRR DON coen E A 3 2 2 ECG Breakout BOX CS prerai ERRE E RE EE did nadas sad ide 4 3 DOR ID en 5 3 1 Environment noise requelion s osso isodsaic is ETA EE 5 4 Callbra tonada 6 5 Principle of the CMRR test asii ria iia 9 5 1 Common mode rejection ratio explained oooocccccoccnncnccnnnonononcnnoncnnncnnonanonnonos 9 5 2 Common mode rejection in ECG equipMeNt cccooccnccnccnncononnnoncnnnnnccnncnncnnnnncnononoonnnnnos 9 do Test COU MAGI enren ar NEEE N a 10 OI ier nn ra ote aid 12 7 Warnings Cautions Notes sossseossossossossssossossosossossossossssossossosessossossossssessossossss 14 e SPE A O 15 9 Contact details esoesoesssssssssssssssssssssssssssosssssssssssssssssssosssssosesossossssssssssssssssssssse 15 aT WHALETEQ 1 Common Mode Rejection Ratio Tester User Manual Introduction WhaleTeq s main focus is on tests in ECG standards is the Single Channel and Multichannel ECG test systems Howe
6. ance is not easy to capacitance obtain An alternate method involves using the 27kQ resistor also used for verifying the WhaleTeg Single channel system With the 27kQ connected between RA and ground the voltage should drop to At 20Vrms 50Hz 16 9 mVrms 10 At 20Vrms 60Hz 20 35mVrms 10 At 20Vrms 200Hz 67 9mVrms 10 A test supply of 200Hz is recommended to minimize the influence of noise If available a low pass filter on the meter should be used to eliminate noise from high frequency sources Inner box 10Vrms when unloaded po at RA or any lead 20D With a 27kQ load the voltage should drop to input after the mV values above transformer e g 20Vrms 200Hz System ground including metal shield under test equipment and meter aY WHALETEQ Common Mode Rejection Ratio Tester User Manual Shield 10Vrms 15 This can be measured indirectly using the internal voltage 50MQ 50kQ divider A measured voltage of 10mVrms between the Monitor and GND terminals is equivalent to 10Vrms To eliminate noise a battery operated meter with short leads located on the GND shield should be used The noise without any voltage applied should ideally be lt 0 5mVrms but not more than 1mVrms If the meter has a low pass filter function this should be used to eliminate noise at higher frequencies e g 1kHz As per the standard this voltage should be adjusted to 10Vrms without the ECG device under test connected If th
7. d for IEC60601 2 47 3 In general even 1mVrms noise equivalent to 1V should not influence a pass fail result If the ECG equipment fails the test indication gt 10mm it may be necessary to reduce noise 12 aY WHALETEQ Common Mode Rejection Ratio Tester User Manual Turn on the supply Using the adjustment capacitor adjust to 10mVrms equivalent to 10Vrms without the ECG device under test connected The adjustment capacitor can be adjusted using a small screw driver Note If metal insulate the portion of the handle of the screwdriver which will be touched with 2 3 turns of electrical tape and adjust the voltage to around 3 5 lower than the target e g 9 5 9 7mV After removing the screwdriver the voltage typically increases 3 5 The adjustment uses a half plate capacitor without an end stop Earlier units used 5 30pF later units use 6 50pF Turn the source off and connect the ECG to the set up RA to RA LA to LA etc keeping the ECG leads above the earthed plane With the source off confirm indication on the ECG is less than 1mm peak to valley peak to peak This is a double check that the environment noise is sufficiently low Turn on the source connect RA to the imbalance terminal and measure the indication on all leads Lead 1 Il Ill V1 V6 Note With RA on the imbalance terminal an indication is expected on Leads Il but not on lead Ill Also a 1 3 indication on chest leads V
8. e ECG breakout box is used this should be connected prior to adjustment The adjustment capacitor can be adjusted using a small screw driver The adjustment uses a half turn capacitor 5 30pF or in later units 6 50pF without an end stop meaning that if it is continued in one direction the voltage will start to increase again Use small incremental adjustments and allow the voltage to stabilize after adjustment It is recommended to use a metal screw driver for good mechanical contact with an insulated handle e g with 3 4 layers of electrical tape if required Using this the voltage is adjusted to be around 3 5 lower than required After removing the screwdriver the voltage will increase 3 5 Using the component tolerances given in the standard an acceptable range is 15 8 5mV 11 5mV However it is recommended to adjust to within 9 5 10 5mV 5 to ensure repeatability of the test Impedance 51kQ 1 This can be measured between Imbalance with DC terminal imbalance and any other lead electrode with the DC offset off R aY WHALETEQ Common Mode Rejection Ratio Tester User Manual Impedance This can be measured between Imbalance with DC imbalance terminal and any other lead with DC offset set to off C Measurement of capacitance in circuit can be done provided that the meter s measurement frequency is 1kHz or higher to minimize the influence of the 51kQ parallel resistor However traceabil
9. epleted and will require replacement This in turn requires disassembly of equipment including the internal shield Later models have made this easier to perform however it is best to avoid this situation by ensuring that the switch is off in normal use 14 aY WHALETEQ 8 Specifications Common Mode Rejection Ratio Tester User Manual Additional Details Specification Design if required capability Input transformer Voltage Step up to allow use with a function generator 1000 1 using 50MQ0 50kQ divider Series capacitance Imbalance impedance R Imbalance impedance C DC offset Environment Assured by selection of components or adjustment 9 Internal battery powered Intended for normal laboratory environment The selection of critical components is known to be stable in the range shown The 50MQ divider may be affected by high humidity in excess of 85 Contact details Ratio not lower than 4 1 e g drive voltage 5Vrms or less is required Ratio accuracy 2 100pF 5 51kQ 1 47nF 5 300mV 1 Up to 50hrs with intermittent use 15 30 C 10 75 RH WHALETEQ Co LTD service whaleteq com 0 886 2 2550 1239 8F 3 No 106 Minquan W Rd Taipei City 10361 Taiwan 15
10. etup 3 1 Environment noise reduction A noise free environment is necessary for testing ECG equipment This can be achieved relatively easily by using a metal bench or metal sheet underneath the ECG device under test the WhaleTeq CMRR test unit and also connecting together the ground as shown Ee A KIA Common Mode Rejection Ratio Test Unit 2 0 ECG Device Frame ground or Under test EP terminal For EC50501 226 227 2 47 2 51 ANSVAAMI EC11 EC13 ECG lead electrodes RA LA LL IRL t V11V2 V3 V4 tvs va gt Tocbrical inverartor from MEDTEO Metal bench metal sheet or foil With this set up turn the ECG device under test to maximum sensitivity turn off the ac filters if possible and with the function generator supply OFF confirm that the noise indication is lt Imm 0 1mVpp aY WHALETEQ Common Mode Rejection Ratio Tester User Manual 4 Calibration As per ISO IEC 17025 the system should be calibrated either before use or on a periodic basis For the CMRR test some compromises must be made due to the nature of the circuit The following process for calibration is recommended Note as tests are infrequent and the calibration method is specialized it is recommended to calibrate before use e Nave fem value Can be measured between the Input and GND voltage terminals using a calibrated meter Source 100pF 5 In general traceability for capacit
11. g tested WhaleTeq s device takes advantage of this to eliminate all switches IEC 60601 2 27 requires a dc offset of 300mV while IEC 60601 2 25 2011 and IEC 60601 2 51 consider that other tests have proved the ability to handle a dc offset The dc offset is sourced by an internal battery The lifetime of this battery is estimated to be at least 50 hrs which should far exceed the lifetime of the equipment if the switch is returned to the Off position after use If the 10 aY WHALETEQ Common Mode Rejection Ratio Tester User Manual DC offset switch is accidentally left on continuously e g while in storage the battery will require replacement Contact WhaleTeq for details if this occurs Test experience indicates that due to the right leg drive there can be short period of 1 2s while the equipment learns the noise This can result in transient response which can be ignored Earlier designs of WhaleTeq equipment incorporated the CMRR test circuit inside the USB module but found that results were not the same as separate double box construction The suspected reason is that the right leg drive is unable to respond correctly if there is other higher frequency noise around 11 aY WHALETEQ Common Mode Rejection Ratio Tester User Manual 6 Operation Operation will typically follow these steps Procedure Diagrams 1 Set up noise free environment as described in Section 3 2 Connect a function generator
12. he IEC standard differs from US and other standards 5 3 Test equipment Refer to the standard for the test circuit From a testing point of view the series 100pF introduces significant complications as it represents a very high impedance of about 30MQ at 50 60Hz This means that attempts to measure the applied voltage 10Vrms with a normal multimeter will fail because the meter has around 10MQ input impedance It is possible to use 1000 1 HV probe with an oscilloscope LOOMQ 3pF but noise and other errors can be large Even 100MQ 3pF will load the circuit so the voltage will change increase by about 5 after the HV probe is removed which should be accounted for if such probes are used WhaleTeq s equipment incorporates a 50MQ 50kQ 1000 1 divider to allow monitoring by a typical digital multimeter 10mVrms 10Vrms The value of 50MQ has been chosen as the best compromise between loading the circuit noise and accuracy As the divider remains in circuit it at all times the unloaded applied voltage without the ECG connected can be considered accurate However the 50MQ can slightly change the loaded voltage once the ECG is connected because it is resistive not capacitive The error introduced will vary based on ECG s capacitance to ground but simulations indicate this error is small and in the very worst case will still be less than 3 The 100pF also creates a problem with the position of the patient cable If the cable is allowed to
13. ity for capacitance is generally impractical An alternate method is used which is based on the loaded output see circuit below For this circuit an 80Hz sine wave source having a source impedance of 51k0 47nF will be loaded by 50 0 500 by a 27kQ resistor A capacitance error of 10 corresponds to variation of 47 8 and 52 2 loading by a 27kQ resistor Imbalance with DC LET FG set to 80Hz m Sinewave eds A7nF 37KO Multimeter Vrms If all values are perfect a 27kQ resistor will load the output by exactly 50 compared to the unloaded value when using 80Hz DC offset 300mV 1 This can be measured between Imbalance with DC terminal and any other lead with DC set to 300mV and or 300mV Note that due to the series resistance of 51kQ the measured value will read 0 5 low if a typical LOMQ input impedance meter is used Therefore the expected reading is 298 5mV This offset is sourced by a small internal battery which is calculated to provide over 24hrs of continuous use and should exceed the lifetime of the equipment aY WHALETEQ Common Mode Rejection Ratio Tester User Manual 5 Principle of the CMRR test 5 1 Common mode rejection ratio explained A perfect device measuring a differential voltage should not respond to the level of common mode voltage which appears at both inputs For example a multimeter where the plus terminal is 100 017V and the minus terminal is 100 001V should theoretically i
14. n is expected due the normal lead relation Repeat the test for all leads by swapping each lead to imbalance terminal in turn Repeat the tests with 300mV and 300mV if required by the standard Note It is recommended to return each lead to their original position after each test to avoid confusion and tangled cables When complete ensure the dc is set to off This ensures the internal battery is not depleted i Em E L CM Fojartion Ratio Tost 0 fe is m s DMM 10 0mVrms E Adjustment capacitor Earthed plane LA LL RL d Inveresticr from MEDTEQ LAIL LLIF RL N CMRR ECG Bres akout Box for IEC60601 2 25 th 1EC60501 2 47 1E esc en cad 13 ECG under test aY WHALETEQ Common Mode Rejection Ratio Tester User Manual 7 Warnings Cautions Notes Please consider the following warnings cautions with this equipment 1 Input other than function generator WARNING If the 20Vrms input is sourced directly bypass the function generator input transformer take appropriate precautions In particular There is no input protection provided Do not apply more than 30Vrms Do not connect a function generator at the same time Use a safety isolation transformer separation between the 20Vrms circuit and accessible parts is not designed for safety insulation 200 2 Residual test set up noise CAUTION It is normal to have a small amount of residual noise of up to immpp when no input is applied
15. ndicate measured voltage of 16mV In practice due to slight differences in resistances used in differential amplifiers some of the common mode voltage will come through as an error The common mode rejection ratio or CMRR indicates the ability of the equipment to reject these common mode voltages A scale of dB is normally used as the ratio can range from as low as 100 up to 100 000 40dB to 100dB A CMRR of 60dB indicates a ratio of 1000 and means that common mode voltages will be reduce by a factor of 1000 In the example given equipment with a CMRR of 60dB would have the common voltage 100V reduced to 10mvV still a significant error relative to the differential voltage of 16mV In practice the common mode voltage is usually not more than 10 times the differential voltage so a CMRR of 60dB would only result in a 0 1 error The most common source of common mode noise is mains voltages i e 50 60Hz Thus CMRR in meters is usually specified at these frequencies But it is important to note that CMRR varies with frequency Common mode rejection also varies with the impedance of the source or more specifically the impedance imbalance as the imbalance also upsets the measurement circuit CMRR for multimeters is typically specified with a 1kQ imbalance 5 2 Common mode rejection in ECG equipment ECG equipment can be subjected to a fairly high common mode voltage from mains noise 50 60Hz and can have a much higher impedance imbalance
16. to the BNC terminal Function 3 l l Generator di o ES es Alternate if bypassing the transformer a test FG E ON Common Mode Rejection Ratio Test supply e g 20Vrms 50 or 60Hz can be a connected directly to the Input In this case Alternate Wi take care with the Warnings and Cautions given a in Section 7 Turn on the source and adjust to the desired voltage 20Vrms by monitoring the voltage between the Input to GND FG 3V rms 50 or 60Hz at least 0 1mV resolution connect to the Monitor and GND terminals Keep the leads and meter on the earthed plane Rejection Ratio Test Unit 2 0 For 1EC50001 2 25 2 27 Verify that with the source off the indication on RN RCN the meter is lt 0 5mV If not check adjust grounding remove nearby noise sources or choose a different location If more than 0 5mV Earthed plane remains record as a potential source of error Some meters have the ability to filter out higher frequency noise above 1kHz use this feature if Using a battery operated digital multimeter with available 5 Ifthe ECG breakout box is used make sure this is TA connected and also above the earthed plane E O E o rae ES A Note This is to fix the unloaded capacitance The i 7 o breakout box adds about 10pF load when sitting on an earthed plane lt gt Earthed plane 2 Use 20Vrms for IEC60601 2 27 IEC60601 2 51 Refer to the standar
17. ver these systems do not cover common mode rejection ratio due to the nature of test double box construction noise free environment To meet this need WhaleTeq has developed a CMRR test box The box is uses the double shield construction according to various IEC standards IEC 60601 2 25 IEC 60601 2 27 IEC 60601 2 47 IEC 60601 2 51 and includes the following special features Switching is eliminated by having the imbalance impedance and dc offset available on a special terminal on the CMRR ECG Breakout box Although the diagram shown in standards has all the switches open for the actual test only one switch is required to be open at a time Rather than switching in the imbalance the user simply changes the external electrode connections to the imbalance terminal Elimination of these switches greatly simplifies the design of the CMRR box The box includes a step up transformer to allow a normal signal generator to be used The tests in IEC 60601 2 25 2011 IEC 60601 2 27 and IEC 60601 2 51 require a 20Vrms supply and most function generators are limited to 7Vrms This feature can be bypassed if desired by connecting directly to the blue input monitor 4mm socket The box includes a 1000 1 SOMQ 50kQ voltage divider to allow monitoring of the applied voltage The standard requires that the unloaded voltage is adjusted to 10Vrms however the source impedance is sufficiently high that it cannot be measured by normal meters A 1000 1 di
18. vider constructed of 50MQ 50kQ and is permanently connected has been found to be the best compromise between accuracy circuit loading noise and input impedance of typical multimeters Using this feature the adjusted voltage should be 10mVrms or 1 1000 of the target voltage The box includes a precision stable 300mV source as used in other WhaleTeq equipment aT WHALETEQ Common Mode Rejection Ratio Tester User Manual 2 Description 2 1 CMRR Box The CMRR box internal construction as below the only features not shown is the internal screen internal box which is provided around the circuit floating at 10Vrms as shown by the blue shading below Transformer Step up to 20Vrms 20Vrms Function Generator Input 3 E 5 gt E E f O Adjustable capacitor 1000 1 divider used to monitor applied voltage 10mV LOVrms For connecting the CMRR Box to test the ECG device use the ECG breakout box provided as explained on the following page Alternately the ECG device under test can be directly connected to CMRR Box using a male D15 connector The pin outs are E 1 RA 4 RL 7 V3 10 V6 cs 2 LA 5 V1 8 V4 11 CMRR inner box 3 LL 6 V2 9 V5 12 DC offset no impedance 13 DC offset impedance The imbalance can be determined by external connections simulating the ECG breakout boxes on the following page aT WHALETEQ Common Mode Rejection Ratio Tester User Manual 2 2 ECG Breakout Boxes
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