1, control circuit design

 

The concussion that the accelerometer that suppress report obtains and oscillatory signal need undertake enlarge and processing with charge amplifier, to excogitate the charge amplifier with a kind of practical economy, the author uses chip of compositive operation amplifier to replace many schism parts of an apparatus to undertake optimizing designing, designed corresponding filter wave circuit

 

Circuit of equivalent of the 1.1 sensor that suppress report

 

The graph presses the equivalent circuit of electric sensor

 

The sensor that suppress report is based on piezoelectric effect design, sensing element is made by the material that suppress report, once be made by outside force,use, surface of the material that suppress report can generate a few weak charge. Suffer in sensitive axis direction when the sensor that suppress report when approach, the charge with contrary polarity generates on two electrode, these two electrode are equivalent to source of a charge (electrostatic generator) . The course changes brief hind gain following equality:

 

 

By go up type is knowable, time constant τ is bigger, charge leak is slower, the measurement of sensor the error is smaller. Sensor and signal input should maintain tall insulation resistance, measure an error in order to avoid the charge that fast leak causes.

 

Change-over circuit of 1.2 charge voltage

 

Graph change-over circuit of 2 charge voltage

 

The output voltage limits of operation amplifier is 0.738~1.758 V. Charge for a long time to avoid capacitor C1, make compositive operation saturated, must join in capacitor C1 paralell connection resistor R2. Another is important action is to introduce dc to lose feedback, restrain the input bias voltage that compositive operation amplifier causes effectively. Of system testing low end frequency is F=1/2πR2C1, the cut-off that inputs signal frequency is 0.1Hz, resistor is R2=10mΩ . The resistor R1 that operation amplifier inversion inputs is protecting circuit and limitation main effect has in electric current. The main function of feedback capacitance C1 is the charge signal that produces sensor changeover is voltage signal, because this turns over capacitor of make a present of,need chooses the capacitance of temperature of low drift, low drift and tall leakage block.

 

Graph the influence that the temperature character of capacitance of feedback of 3 different material outputs to switch circuit

 

Author of the plan on the basis chose polystyrene capacitor, reduce what environmental change causes to measure an error.

 

Graph design of circuit of enlarge of 4 segregation voltage

 

The input limits that outputs limits and follow-up AC/DC transformer because of the voltage of charge amplifier is abhorrent, use voltage to magnify circuit will adjust so voltage, make U02 inputs voltage to be changed into U03 of alternating voltage signal.

 

The author is used high-ranking low connect filter to undertake further processing to signal, check noise signal and effective signal mix fold. The author’s will common filter: Butterworth filter, elliptical function filter, Bessel filter undertook contrast, chose LTC1569 filter finally, because of its admirable photograph frequency characteristic and the linear and phasic character that signal is taking the output defer inside and bandpass is basic and identical. What comprise by LTC1569 is low the dc that connects filter slants buy output error is minor, bandpass has linear and phasic character, can protect signal not lack fidelity, make sure signal measures the accuracy of the result.

 

Graph 5 low connect filter

 

Although LTC1569 filter is OK the filter that offers high quality is characteristic, but principle of chip filter wave is to be based on switch capacitance effect, in output end produces noise of high frequency switch, undertake to switch noise through increasing noise of a switch filter wave is passed add a 2 class low filter of the LTC1569 after connecting filter.

 

Graph the comparison that 6 filter divide weaveform of switch noise around

 

2, experimental result and analysis

 

Include what oscillatory signal recuperates circuit to measure a system to will press electric sensor and join of amplitude modulation circuit to rise above all, with the validity of circuit of tuning of test and verify, the picture of sine scanning experiment that through the measurement that linear drafts to add up to demarcate the system gets is as follows:

 

Graph curve of sweep of sine of the 7 sensor that suppress report

 

Use a signal generator to undertake scanning to recuperating circuit to check, got 8 shown channel frequency answer a curve is like a graph:

 

Graph 8 frequency answer a curve

 

Regard vibration of charge source imitate as the output of sensor with standard charge generator, receive its repeatedly measure circuit to go up, voltage is worth computational theory, what measure voltage and theoretical value to agree basically, the measurement that recuperates circuit the error is less than 1% , can satisfy oscillatory signal to gauge the demand of precision, measure oscillatory signal well and truly.

 

3, summary

 

The article is research target with pressing electric sensor, introduced sensor equivalent in detail circuit and adjust circuit, right adjustment the capacitance of circuit key component and filter had analysis and research, gave out the reasonable solution inside limits of author place consideration, had a test to this plan, acquisition data has taller precision, the dependability that collects oscillatory signal data is this circuit and practical provided reliable data support.