ENDEVCO 2680 Series, Instruction Manual

Page 1: ...IM2680 Revision B Nov 1 91 MODEL 2680M1 M7 2680M12 M14 2680M61 67 2681M1 M7 2685M1 M7 AIRBORNE CHARGE AMPLIFIER INSTRUCTION MANUAL ...

Page 2: ...IM2680 Revision B Nov 1 91 San Juan Capistrano Calif ornia U S A ...

Page 3: ...PECTION 2 1 2 INSTALLATION 2 1 SECTION 3 PRE OPERATION TEST 1 INTRODUCTION 3 1 2 EQUIPMENT REQUIRED 3 1 3 VOLTAGE INSERTION TEST PROCEDURE 3 2 4 ALTERNATE TEST METHOD 3 3 SECTION 4 OPERATIONAL CHECKOUT PROCEDURE 1 USING THE CHARGE AMPLIFIER 4 1 2 GAIN ADJUSTMENT 4 1 3 AMPLITUDE LINEARITY 4 2 4 FREQUENCY RESPONSE 4 3 5 DC TO DC CONVERTER 4 3 APPENDIX A THEORY OF OPERATION 1 INTRODUCTION A 1 2 CHARG...

Page 4: ...ON TEST SETUP 3 2 3 2 ALTERNATE CHARGE INSERTION TEST SETUP 3 3 4 1A TYPICAL SYSTEM CONNECTIONS WITH CHARGE AMPLIFIER 4 2 4 1B TYPICAL SYSTEM CONNECTIONS WITH ISOTRON CONDITIONER 4 2 A 1 PIEZOELECTRIC TRANSDUCER EQUIVALENT CIRCUIT A 1 A 2 BASIC AIRBORNE CHARGE AMPLIFIER FUNCTIONAL BLOCK DIAGRAM A 3 A 3 TYPICAL SYSTEM EQUIVALENT CIRCUIT A 4 B 1 TYPICAL GAIN CALIBRATION TEST SETUP B 2 B 2 GAIN ADJUS...

Page 5: ...verter 2685 Endevco Connector DC to DC Converter Integral Electronic Conditioner with constant current supply Each basic model consists of a series of modifications M series to provide seven different gain ranges and nine different high frequency responses The M series covered by this Instruction Manual are M1 thru M7 M12 and M14 Table 1 2 lists the M series and provides a comparison of their inpu...

Page 6: ...Potting Sleeve VikingVS4 16C9 Mounting Hardware Two 6 32 Captive Screws w Lockwashers ______________________________________________________________________________________________________ TABLE 1 1 CONNECTORS ACCESSORIES AND POWER REQUIREMENT 3 OUTPUTS Each Charge Amplifier has two outputs biased and or unbiased The outputs can be a combination of a biased and an unbiased or both outputs can be b...

Page 7: ... Vp p 4 25 Vp p 4 65 Vp p 0 465 mA p p Unbiased 1 64 Vrms 1 5 Vrms 1 64 Vrms 0 164 mA rms M 7 500 10 to 100 2 0 Biased 2 5 V 0 00 V 4 65 Vp p 4 25 Vp p 4 65 Vp p 0 465 mA p p Unbiased 1 64 Vrms 1 5 Vrms 1 64 Vrms 0 164 mA rms M12 Low 5 000 1 0 to 10 1 5 Biased 2 5 V 0 00 V 4 65 Vp p 0 465 mA p p Gain 1 64 Vrms 0 164 mA rms High 5 000 10 to 100 7 5 Biased 2 5 V 0 00 V 4 65 Vp p 0 465 mA p p Gain 1 ...

Page 8: ... Accelerometers Microphones Force Gages or Pressure Pickups The small size light weight low power consumption and the use of long cables to connect Transducers to the Charge Amplifier enables the unit to be used in ground and laboratory testing rocket test stands combined environmental testing steam turbines and other industrial applications ________________________________________________________...

Page 9: ...ies listed in Table 1 1 are included in the shipment with each Charge Amplifier 2 INSTALLATION The Charge Amplifier case is drilled with two holes for mounting the unit to the test specimen The mounting holes vary in size and placement for each Charge Amplifier thus the user should refer to the appropriate Product Data Sheet or Performance Specification for an outline drawing depicting the mountin...

Page 10: ...ge must be established The output voltage established must be less than the Charge Amplifier s full scale output maximum 5 V p p or 1 77 V rms As an example the 2680M1 has a maximum linear biased output of 4 65 V p p 1 64 V rms into a 10 000 ohm load Thus the output established for a 2680M1 should be less than 4 64 V p p Normally an output voltage is selected which is easily read on the readout de...

Page 11: ...ometer and Cable Assembly Calibration Cards for capacitance of each item Use the following formula to determine total capacitance Cin seen at Charge Amplifier s input Cin Cp Cc where Cp Internal Capacitance of Accelerometer Cc Cable Capacitance between Accelerometer and T Block D Establish an Output Voltage Eo for Charge Amplifier The Output Voltage should be less than the maximum linear output fo...

Page 12: ...or s output to Ein and applying this voltage to the input of the T Block H Since both an input Ein and output Eo has been established and verified the Voltage Insertion Test can now be used to verify system integrity anytime the system is suspected of being faulty or assurance that the system is performing to specification I Set switch S1 to OPR operate position and S2 to OUT position for normal s...

Page 13: ...ximum Linear Output for the applicable Charge Amplifier E Again the formula for input versus output is Eo x 103 Ein Aq x Cin where Eo Output Voltage in volts Ein Input Voltage to T Block form Oscillator in volts Aq Charge Amplifier Gain in mV pC see paragraph 4 2 Cin Input Capacitance in pF Includes Accelerometer Capacitance Cp and Cable Capacitance Cc between Accel and T Block F Repeat steps 3 3 ...

Page 14: ...e with the input The 1 10 mV pC low gain outputs of the M12 and M14 are in phase with the input signal while the 10 100 mV pC high gain outputs of the M12 and M14 are 180 out of phase with the input 2 GAIN ADJUSTMENT Each Charge Amplifier provides two outputs and Gain Potentiometer is common to both outputs Those Charge Amplifiers M12 and M14 with dual biased or dual unbiased outputs have a 10 1 r...

Page 15: ...rgize equipment and allow 15 minutes to temperature stabilize C Adjust power supply for 28 V dc output D Set Voltage Divider Potentiometer to its maximum output fully CW E Adjust Oscillator Frequency for 100 Hz and set test setup switch S1 to OUT position and then adjust Oscillator Output Amplitude until Charge Amplifier s output is 100 mV below clip level on Oscilloscope note DVM for mV rms indic...

Page 16: ... setup switch S1 to 1N position Verify Oscillator Output Amplitude is still 1 0 V rms and then set switch to OUT position NOTE A Charge Amplifier s frequency range of interest depends on type of filter used Refer to Table 1 3 for Model versus Frequency Range I Vary Oscillator Frequency over Charge Amplifier s range of interest and observe Oscilloscope and DVM for Gain versus Frequency Response The...

Page 17: ...ALENT CIRCUIT A simplified equivalent circuit of a Piezoelectric or Capacitive Transducer is shown in Figure A 1 The open circuit voltage Eo is equal to the charge q divided by the Transducer Capacitance Cp as noted in the following formula Eo q Cp where Eo is expressed in V q is expressed in pC Cp is expressed in pF If the Open Circuit Voltage is known the Transducer charge can be calculated by q...

Page 18: ...ucer no additional calculations are necessary For example the typical voltage sensitivity Ecal of the Endevco Model 2272 Accelerometer is 4 0 mV g typical capacitance is 2700 pF and the Accelerometer is calibrated with 300 pF of external capacitance Thus the typical Charge Sensitivity is Qs 4 2700 300 1000 12 pC g 2 CHARGE CONVERTER A functional block diagram of a basic Airborne Charge Amplifier i...

Page 19: ...ain Range The Gain is externally adjusted after removal of an Access Screw Both the Charge Converter and Voltage Amplifier Gains are fixed for optimum stability 4 VOLTAGE AMPLIFIER The final stage of the Charge Amplifier is a Voltage Amplifier Because of its low output impedance and 0 5 mA minimum output current the Charge Amplifier is capable of driving tape recorders directly The outputs are bot...

Page 20: ...t shown Cp is the Transducer Capacitance Cf is the total external shunt cable capacitance and Cp Cf is the total source capacitance for the Charge Amplifier FIGURE A 3 TYPICAL SYSTEM EQUIVALENT CIRCUIT The Charge Gain in mV pC of the system is defined by the formula Eo Aq _____ q in where Aq Charge Gain of Charge Amplifier in mV pC Eo Charge Amplifier output in mV qin Charge Amplifier input Transd...

Page 21: ...ut in mV pk FS Charge amplifier s desired peak full scale output in g pk The Amplifier s Charge Gain Setting Aq is computed by As Aq ______ Sq where Aq Amplifier s Charge Gain setting in mV pC Sq Transducer s Charge Sensitivity in pC g As an example suppose a system consisting of an Endevco Model 2680 Series Charge Amplifier which has a 2 5 V pk or 2500 mV pk full scale output and an Endevco Model...

Page 22: ...ibration Figure B 1 is a typical test setup used for Gain Calibration FIGURE B 1 TYPICAL CALIBRATION TEST SETUP To charge applied to the input of Charge Amplifier in Figure B 1 is determined by qcal Ecal Ccal where Ecal Oscillator output in V Ccal Series calibration capacitor in pF qcal Charge applied to the Charge Amplifier in pC The Charge Gain of the Amplifier Aq is determined by Eout As Aq ___...

Page 23: ...arge Amplifiers Access Screws can be procured from Endevco under part number 1103 see Table B 1 Table B 1 lists the equipment required to remove and seal the Gain Access Screw and to adjust the Gain of the Charge Amplifier as defined ________________________________________________________________________ ITEM PURPOSE ________________________________________________________________________ Power s...

Page 24: ...rom entering Charge Amplifier interior E Apply torque CW to Allen wrench and remove the access screw when the solder seal is molten 5 SEALING ACCESS SCREWS New Access Screws should always be used to seal the gain adjust hold Installing used Access Screws could prevent the Charge Amplifier from meeting humidity specifications A Install a new Access Screw in gain adjust hold B Preheat oven to a temp...

Page 25: ...ENDEVCO 2680 INSTRUCTION MANUAL IM2680 Page B 5 FIGURE B 2 GAIN ADJUSTMENT FOR CHARGE AMPLIFIERS WITHOUT DC TO DC CONVERTERS FIGURE B 3 GAIN ADJUSTMENT FOR CHARGE AMPLIFIERS WITH DC TO DC CONVERTERS ...