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REV NR, ECO 54817
8/21/24
Piezoelectric accelerometers
ENDEVCO
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Piezoresistive accelerometers
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IEPE accelerometers
intensity microphones
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Inertial sensors
www.endevco.com
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Variable capacitance accelerometers
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Signal conditioners and supportive instrumentation
Tel: +1 (866) ENDEVCO [+1 (866) 363-3826]
Model 2680B
Airborne Amplifier
Instruction Manual # 77079
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Piezoresistive pressure sensors
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Piezoelectric pressure sensors
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Cable assemblies
IM 2680B 77079 013124
®
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High
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Table of Contents
Related Manuals for ENDEVCO 2680B
Summary of Contents for ENDEVCO 2680B
- Page 1 Piezoelectric accelerometers Piezoresistive accelerometers IEPE accelerometers Variable capacitance accelerometers Piezoresistive pressure sensors Piezoelectric pressure sensors High intensity microphones Inertial sensors Signal conditioners and supportive instrumentation Cable assemblies ENDEVCO www.endevco.com Tel: +1 (866) ENDEVCO [+1 (866) 363-3826] IM 2680B 77079 013124...
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Page 2: Table Of Contents
07 MAINTENANCE AND CALIBRATION ....................19 7.1 Returning the Unit ............................19 APPENDIX A: CABLE INSTALLATION RECOMMENDATIONS ............. 20 APPENDIX B: WHY A CALIBRATION CAPACITOR? ................21 Tel: +1 (866) ENDEVCO [+1 (866) 363-3826] ENDEVCO www.endevco.com IM 2680B 77079 013124... -
Page 3: Products Covered
Table 1: “M” number nomenclature for the 2680B Low-Pass Filters The 2680B includes a three-pole Butterworth low-pass filter. The model number will contain a three- digit suffix (dash number) to indicate the filter’s -5% frequency in Hz. The first two digits are significant numbers, and the third indicates the numbers of zeroes. -
Page 4: Product Description
The 2680B’s front end has a charge converter, followed by a voltage amplifier at the output. The charge amplifier produces an output voltage proportional to the charge at the input, thus minimizing the effect of input cable length. -
Page 5: Installation
92147A420 Optional mating connector EDVEJ1125 Glenair 800-008-06Z16-7SN Optional EMI band EDVEP636 Glenair 600-057-1 Table 3: Standard accessories supplied Figure 2: Outline drawing of the 2680B charge amplifier Tel: +1 (866) ENDEVCO [+1 (866) 363-3826] ENDEVCO www.endevco.com IM 2680B 77079 013124... -
Page 6: Grounding
If the case is grounded to the frame of the test article, it is advisable to reference the signal/power ground to this same frame ground. This can be achieved by connecting pin 3 to pin 2 in the 2680B output connector and tying pin 2 to the return of a floating power source. If the power source is not floating (referenced to the frame ground), then the power source ground should connect to pin 2 of the output connector but NOT be connected to pin 3 to avoid a ground loop. -
Page 7: Output Connector
AC signal to be available at pin 6. With the addition of the series capacitor and bleed resistor at the output, a 0.00 VDC bias level is established. The unbiased output is linear Tel: +1 (866) ENDEVCO [+1 (866) 363-3826] ENDEVCO www.endevco.com... -
Page 8: Adjustable Gain/Sensitivity
0 to 4.65 Vpp. 04.6 Adjustable Gain/Sensitivity The airborne amplifier’s gain/sensitivity can be adjusted digitally; either at the factory, or using Endevco Model 4876 Handheld Gain Programmer. By default, units will have the gain set to the minimum rated gain. See... -
Page 9: How To Calculate Gain And Output Level
The signal source should be set to 100Hz. For example, suppose a system consisting of a charge-mode piezoelectric accelerometer is used to measure ± 50g peak, full scale with a 2680B amplifier (which has a 2500 mV full-scale output). Using the previous equation:... -
Page 10: What To Look For
The below image shows the spectrum of an undistorted sine wave. Only a single frequency is present. Figure 3B: FFT showing a clean sine wave in the frequency domain ENDEVCO www.endevco.com Tel: +1 (866) ENDEVCO [+1 (866) 363-3826] IM 2680B 77079 013124... - Page 11 Figure 3D is an example of the presence of clipping as seen in the time domain. In this case, further analysis using the FFT mode is unnecessary since the problem is obvious. Figure 3D: A distorted sine wave in the time domain ENDEVCO www.endevco.com Tel: +1 (866) ENDEVCO [+1 (866) 363-3826] IM 2680B 77079 013124...
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Page 12: Environmental Considerations
As an example, let’s assume that we are going to use a model 2230 high- temperature accelerometer. The room temperature resistance is 1GΩ, which would work well with the 2680B. However, the resistance drops to 100kΩ when the accelerometer reaches 900°F (482°C). The system is now starting to become susceptible to low-frequency peaking. -
Page 13: Performance Testing
It is sometimes desirable (or required) to test the integrity of a system after installation. This section will provide both a quick test and an in-depth test for the 2680B. The quick test might be conducted prior to installation to verify the unit is operational. -
Page 14: Handheld Shaker Method
Set the reference shaker frequency to 100Hz. Observe a 100 Hz undistorted sine wave on the oscilloscope. If the oscilloscope is DC coupled, a DC bias of 2.50 VDC (±3%) should also be observed. Tel: +1 (866) ENDEVCO [+1 (866) 363-3826] ENDEVCO www.endevco.com... -
Page 15: Accelerometer Simulator Method
6.1.2 Accelerometer Simulator Method An accelerometer simulator is also a good source for testing the performance of the 2680B. In this instance, the accelerometer is absent from the circuit. The Endevco model 4830B (figure 6) is an example of an accelerometer simulator. -
Page 16: Quick Test
If a suitable response is observed on the oscilloscope, the test is complete. Figure 7: The left side of the trace shows the initial strike followed by the “ring” from the accelerometer’s resonance. Other patterns are possible from a “good” system. Tel: +1 (866) ENDEVCO [+1 (866) 363-3826] ENDEVCO www.endevco.com... -
Page 17: Testing Without A Sensor
2947C Calibration Capacitor. The 2947C is simply a stable, well-shielded 1000pF capacitor that is placed between the signal generator and the 2680B charge amplifier. Its purpose is to convert the signal generators output voltage to a charge (pC) signal. When using a 1000 pF capacitor, charge = voltage. - Page 18 Figure 9: Test set- up using a sine wave voltage signal. The 2947C converts the voltage (mV) signal to a charge signal (pC). The output wave is displayed on the oscilloscope and the bias voltage is read on the DMM. Tel: +1 (866) ENDEVCO [+1 (866) 363-3826] ENDEVCO www.endevco.com...
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Page 19: Maintenance And Calibration
RMA number on the enclosed documentation and the outside of the shipping box. Include a description of the problem encountered and the unit serial number and your contact information. Outside USA: Contact your local representative or distributor and follow their instructions. Tel: +1 (866) ENDEVCO [+1 (866) 363-3826] ENDEVCO www.endevco.com... -
Page 20: Appendix A: Cable Installation Recommendations
Replace any noisy cables. If you make your own connector-coaxial cable assemblies, cut and strip the cable carefully. When using low-noise cable on the 2680B, don’t smear the electrically conductive coating across the dielectric. Do not allow cable to be dropped, contaminated, stepped on or otherwise abused. Treat it as carefully as you would treat your transducer. -
Page 21: Appendix B: Why A Calibration Capacitor
100 Hz; thus this frequency is the recommended input to be used for this test. The uncertainty will be that of the signal source and the capacitor. The Endevco 2947C has an uncertainty of ±1%. Adequate shielding is required for optimum accuracy. The amplifier, being a high impedance device, is sensitive to ambient noise.
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