CN102944249A - Measuring device for measuring output signals of passive sensor and signal detecting system - Google Patents

Abstract

The invention is suitable for the technical field of signal detection and processing, and provides a measuring device for measuring output signals of a passive sensor and a signal detecting system; the measuring device comprises an amplifying circuit, a driving circuit and a microprocessor, wherein the microprocessor includes a timer, an analog-digital converter and a serial communication interface. The measuring device provided by the invention outputs the excitation voltage or current through the drive circuit according to square-wave signals output by the microprocessor, and enables the passive sensor to periodically work between an excitation state and a non-excitation state; the microprocessor performs the difference calculation and the average calculation for digital signals which are obtained in the middle time of the two working states of the passive sensor in a plurality of periods, and the calculation results are used as the output signals of the passive sensor, and are output to a computer for processing through the serial communication interface, so that the interference and the noise influence are reduced largely, the signal-to-noise improvement factor is greater, and the measuring precision is higher.

Description

A kind of measurement mechanism and signal detection system of measuring the passive sensor output signal

Technical field

The invention belongs to input and processing technology field, more specifically, relate to a kind of measurement mechanism and signal detection system of measuring the passive sensor output signal.

Background technology

In a large amount of industry spot and scientific research and testing, passive sensor often causes larger measuring error because working environment has than strong jamming, and for example the optical fiber freezing sensor very easily is subjected to the impact that bias light disturbs, and light source luminescent intensity also easily fluctuates.Simultaneously, passive sensor metering circuit itself is also because the variation of working environment causes measuring error, and for example the zero-point voltage of pre-amplification circuit is understood variation with temperature and drifted about.

Summary of the invention

For the defective of prior art, the object of the present invention is to provide a kind of measurement mechanism of measuring the passive sensor output signal, be intended to solve existing measurement mechanism causes measuring error because of the variation of working environment problem.

For achieving the above object, the invention provides a kind of measurement mechanism for measuring the passive sensor output signal, comprise amplifying circuit, driving circuit and microprocessor; Described microprocessor comprises timer, analog to digital converter and serial communication interface; The input end of described amplifying circuit is connected with passive sensor, and the output terminal of described amplifying circuit is connected with described analog to digital converter; The input end of described driving circuit is connected with described timer, and the output terminal of described driving circuit is connected with described passive sensor; Described serial communication interface is connected with the computing machine of outside; Described driving circuit according to the square-wave signal output drive voltage of described microprocessor output or electric current and so that described passive sensor between foment and nonexcited state, periodically work; Described amplifying circuit is enlarged into analog voltage signal with the electric signal of described passive sensor output; Described analog to digital converter is converted to digital signal with described analog voltage signal; Described microprocessor is asked poor and average computation with the digital signal that constantly obtains in the middle of two kinds of duties of described passive sensor in a plurality of cycles, and result of calculation is exported to Computer Processing as the output signal of described passive sensor and by described serial communication interface.

Further, described passive sensor is thermistor, voltage dependent resistor (VDR), humicap or optical fiber freezing sensor.

Further, described microprocessor is single-chip microcomputer or dsp chip.

Further, described driving circuit comprises: the first resistance, the first electric capacity, the first switching tube; One end of described the first resistance is as the output head anode of described driving circuit, the other end connection+5V voltage of described the first resistance; One end of described the first electric capacity is connected to described+5V voltage, the other end ground connection of described the first electric capacity; The control end of described the first switching tube is as the input end of described driving circuit, and the first end of described the first switching tube is as the negative pole of output end of described driving circuit, the second end ground connection of described the first switching tube; The control end of described the first switching tube is controlled the conducting between its first end and the second end.

Further, described the first switching tube is triode, the base stage of described triode is as the control end of described the first switching tube, and the collector of described triode is as the first end of described the first switching tube, and the emitter of described triode is as the second end of described the first switching tube.

Further, described amplifying circuit comprises: the second resistance, the 3rd resistance, the second electric capacity, the 3rd electric capacity, amplifier, the first one-way conduction element, the second one-way conduction element; Described amplifier comprises 8 ports, the 1st port is connected to the 8th port by the second resistance and the 3rd resistance successively, the 2nd port is as the input cathode of described amplifying circuit, the 3rd port is as the input anode of described amplifying circuit, and the 4th port connects-12V voltage, and the 4th port is also by the 3rd capacity earth, the 5th port ground connection, the 6th port is as the output terminal of described amplifying circuit, and the 7th port connection+12V voltage, the 7th port are also by described the second capacity earth; Described the first one-way conduction element and described the second one-way conduction element be connected in turn+3.3V voltage and ground between, described the first one-way conduction element and described the second one-way conduction element be connected in series the 6th port that end is connected to described amplifier.

Further, described the first one-way conduction element is the first diode, the negative electrode connection+3.3V voltage of described the first diode, and the anodic bonding of described the first diode is to the 6th port of described amplifier.

Further, described the second one-way conduction element is the second diode, and the negative electrode of described the second diode is connected to the 6th port of described amplifier, the plus earth of described the second diode.

Measurement mechanism provided by the invention by driving circuit according to the square-wave signal output drive voltage of microprocessor output or electric current and so that passive sensor between foment and nonexcited state, periodically work; By microprocessor the digital signal that constantly obtains in the middle of two kinds of duties of passive sensor in a plurality of cycles is asked poor and average computation again, result of calculation is exported to Computer Processing as the output signal of passive sensor and by serial communication interface; Greatly reduce the impact of interference and noise, had larger noise to improve ratio and higher measuring accuracy.

Another object of the present invention is to provide a kind of signal detection system, comprise the passive sensor, measurement mechanism and the computing machine that connect successively; Described measurement mechanism is exported to Computer Processing with the output signal of described passive sensor; This measurement mechanism is above-mentioned measurement mechanism.Adopt above-mentioned measurement mechanism that the output signal of passive sensor is measured, measuring accuracy is high, simple and reliable and cost is low.

Description of drawings

Fig. 1 is the modular structure synoptic diagram of the measurement mechanism of the measurement passive sensor output signal that provides of the embodiment of the invention;

Fig. 2 is the physical circuit figure of amplifying circuit in the measurement mechanism that provides of the embodiment of the invention;

Fig. 3 is the physical circuit figure of microprocessor in the measurement mechanism that provides of the embodiment of the invention;

Fig. 4 is the physical circuit figure of driving circuit in the measurement mechanism that provides of the embodiment of the invention;

Fig. 5 is that measurement mechanism that the embodiment of the invention provides is applied to the principle schematic in the optical fiber freezing sensor.

Embodiment

In order to make purpose of the present invention, technical scheme and advantage clearer, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that specific embodiment described herein only in order to explain the present invention, is not intended to limit the present invention.

In order to make purpose of the present invention, technical scheme and advantage clearer, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that specific embodiment described herein only in order to explain the present invention, is not intended to limit the present invention.

The measurement mechanism of measurement passive sensor output signal provided by the invention is mainly used in intelligent signal detection and treatment technology and reliability measurement technical field, and this measurement mechanism is a kind of high-precision measurement circuit of eliminating or reducing measurements interference and noise; Have general and obvious realistic meaning.

Fig. 1 shows the modular structure of the measurement mechanism of measurement passive sensor output signal provided by the invention, for convenience of explanation, only shows the part relevant with the embodiment of the invention, and details are as follows:

The measurement mechanism 2 that is used for measurement passive sensor output signal that is connected between passive sensor 1 and the computing machine 3 comprises: amplifying circuit 21, driving circuit 23 and microprocessor 22; Microprocessor 22 comprises: timer 2 22, analog to digital converter 221 and serial communication interface 223; Wherein, the input end of amplifying circuit 21 is connected with passive sensor 1, and the output terminal of amplifying circuit 21 is connected with analog to digital converter 221; The input end of driving circuit 23 is connected with timer 2 22, and the output terminal of driving circuit 23 is connected with passive sensor 1; Serial communication interface 223 is connected with the computing machine 3 of outside; Driving circuit 23 according to the square-wave signal output drive voltage of microprocessor 22 output or electric current and so that passive sensor 1 between foment and nonexcited state, periodically work; Amplifying circuit 21 is enlarged into analog voltage signal with the electric signal of passive sensor 1 output; Analog to digital converter 221 is converted to digital signal with analog voltage signal; Microprocessor 22 is asked poor and average computation with the digital signal that constantly obtains in the middle of 1 two kinds of duties of passive sensor in a plurality of cycles, and result of calculation is exported to computing machine 3 processing as the output signal of passive sensor 1 and by serial communication interface 223.

Measurement mechanism provided by the invention is a kind of anti-jumming measuring circuit that is applicable to passive sensor, comprising: microprocessor 22, driving circuit 23 and amplifying circuit 21; Microprocessor 22 utilizes the square-wave signal of the comparing unit generation constant frequency of timer internal 222, and exports from the IO port; Driving circuit 23 receives output drive square wave behind the square wave that microprocessor 22 produces, and this square wave both can be voltage signal, also can be current signal.The high voltage of square wave or large electric current make passive sensor work in foment, and low-voltage or little electric current make passive sensor work in nonexcited state.Therefore, passive sensor 1 will be between foment and nonexcited state switch operating state periodically; Amplifying circuit 21 has high input impedance, low-noise characteristic, and it is enlarged into analog voltage signal with voltage or the current signal of passive sensor 1 output; This analog voltage signal is converted to digital signal by the analog to digital converter 221 of microprocessor 22 inside; Microprocessor 22 calculates first the difference of the passive sensor 1 different digital signal that moment analog to digital converter obtains in the middle of same square-wave cycle underexcitation state and nonexcited state, calculate the mean value of these differences in a period of time that comprises many square-wave cycle, this result of calculation is as the output signal of passive sensor 1 again; The output signal of passive sensor device 1 can be exported to computing machine 3 by the serial communication interface 223 of microprocessor 22 inside and make further analyzing and processing.

In the present invention, passive sensor 1 is sensitive element, itself without direct energy conversion ability, can only with a class sensor of the electrical characteristics of input signal change itself, can be thermistor, voltage dependent resistor (VDR), humicap or optical fiber freezing sensor.This passive sensor 1 must adopt the extrinsic motivated source that passive sensor is encouraged, and just can obtain output signal.

In the present invention, amplifying circuit 21 is to have high input impedance, high-gain, low noise accurate voltage amplifying circuit or current amplification circuit; Fig. 2 shows the particular circuit configurations of this amplifying circuit 21; Details are as follows:

Amplifying circuit 21 comprises: the second resistance R 2, the 3rd resistance R 3, the second capacitor C 2, the 3rd capacitor C 3, amplifier U1, the first one-way conduction element, the second one-way conduction element; Amplifier U1 comprises 8 ports, the 1st port is connected to the 8th port by the second resistance R 2 and the 3rd resistance R 3 successively, the 2nd port is as the input cathode of amplifying circuit 21, the 3rd port is as the input anode of amplifying circuit 21, and the 4th port connects-12V voltage, and the 4th port is also by the 3rd capacitor C 3 ground connection, the 5th port ground connection, the 6th port is as the output terminal of amplifying circuit 21, and the 7th port connection+12V voltage, the 7th port are also by the second capacitor C 2 ground connection; The first one-way conduction element and the second one-way conduction element be connected in turn+3.3V voltage and ground between, the first one-way conduction element and the second one-way conduction element be connected in series the 6th port that end is connected to amplifier.

In embodiments of the present invention, the 3rd resistance R 3 is adjustable resistance, resistance 10K.The first one-way conduction element can be the first diode D1, and wherein, the negative electrode of the first diode D1 connects voltage+3.3V, and the anodic bonding of the first diode D1 is to the 6th port of amplifier.The second one-way conduction element can be the second diode D2, and wherein, the negative electrode of the second diode D2 is connected to the 6th port of amplifier, the plus earth of the second diode D2.The first one-way conduction element and the second one-way conduction element can also can be realized for other components and parts of one-way conduction.

In the present invention, microprocessor 22 has been integrated timer itself, has kept single-chip microcomputer or the dsp chip of integral analogue-to-digital converter, reference voltage generator and the serial communication interface of function with sampling; Its physical circuit as shown in Figure 3, microprocessor 22 comprises MCU chip U2, interface chip U3 and peripheral circuit thereof.The dutycycle of the square wave that microprocessor 22 produces is 50%, and its frequency is comprehensively to determine according to the processing power of the dynamic perfromance of passive sensor and microprocessor.Suitably increase frequency, be conducive to make interference that the present invention can resist or eliminate and the frequency band of noise to broaden; But this frequency again can not be too high, the one, because need certain rise time or fall time during between excitation and two kinds of duties of non-excitation, the switching of passive sensor, and the 2nd, because the switching rate of analog to digital converter is limited.Collection and the conversion of 221 pairs of analog voltage signals of analog to digital converter in the microprocessor 22 are in that constantly each generation is once constantly and in the middle of low level in the middle of the high level in each cycle of square-wave signal.Determining of " constantly middle " is to realize by the timer 2 22 of microprocessor 22.Wherein selected " a period of time " of average computation, comprise an integer square-wave cycle, and periodicity is much larger than 1.This section period is the integral multiple of power frequency period, disturbs in order to eliminate power frequency; But this section period proper extension, with the raising measuring accuracy, but the time again can not be oversize, measures real-time in order to avoid reduce.

In the present invention, to be output signals identical with the waveform of input signal, phase place is identical or opposite and can be to the enough circuit of large exciting current of passive sensor output for driving circuit 23; Fig. 4 shows the particular circuit configurations of this driving circuit 23; Details are as follows:

Driving circuit 23 comprises: the first resistance R 1, the first capacitor C 1, the first switching tube; One end of the first resistance R 1 is as the output head anode of driving circuit 23, the other end connection+5V voltage of the first resistance R 1; One end of the first capacitor C 1 is connected to+5V voltage, the other end ground connection of the first capacitor C 1; The control end of the first switching tube is as the input end of driving circuit 23, and the first end of the first switching tube is as the negative pole of output end of driving circuit 23, the second end ground connection of the first switching tube; The control end of the first switching tube is controlled the conducting between its first end and the second end.

In the present invention, the first switching tube can play for triode, metal-oxide-semiconductor or controllable silicon etc. the components and parts of on-off action; When the first switching tube was triode Q1, the base stage of triode Q1 was as the control end of the first switching tube, and the collector of triode Q1 is as the first end of the first switching tube, and the emitter of triode Q1 is as the second end of the first switching tube.

Measurements interference and noise can be eliminated or reduce to measurement mechanism provided by the invention; Mainly be to have utilized sync correlation to detect this intelligent signal to detect and treatment technology, details are as follows particularly:

(1) establishing the measurement initial time is 0, and the cycle of excitation square wave is T, and the t constantly output voltage of amplifying circuit is v (t), and sensor output effective voltage is v _e(t), the circuit zero-point voltage is v _z(t), environmental interference voltage is v _i(t), circuit noise voltage is v ₀(t), v (t)=v then _e(t)+v _z(t)+v _i(t)+v _n(t);

(2) moment (3T/4,7T/4,11T/4...) in the middle of square wave is low level, working sensor is in nonexcited state, and sensor output effective voltage is zero, so

$v\left(\frac{2n+3}{4}T\right)=v_z\left(\frac{2n+3}{4}T\right)+v_i\left(\frac{2n+3}{4}T\right)+v_n\left(\frac{2n+3}{4}T\right),n=\mathrm{0,1,2},...;$

(3) moment (T/4,5T/4,9T/4...) in the middle of the square wave high level, working sensor is in foment, and sensor output effective voltage is non-vanishing, so

$v\left(\frac{2n+1}{4}T\right)=v_e\left(\frac{2n+1}{4}T\right)+v_z\left(\frac{2n+1}{4}T\right)+v_i\left(\frac{2n+1}{4}T\right)+v_n\left(\frac{2n+1}{4}T\right),n=\mathrm{0,1,2},...;$

(4) N all after date carried out in measurement, and the formula of microprocessor calculating sensor output effective voltage is: $\stackrel{\‾}{v_e\left(t\right)}=\frac{1}{N}[\underset{n=\mathrm{0,2}}{\overset{2N-2}{\mathrm{\Σ}}}v\left(\frac{2n+1}{4}T\right)-\underset{n=\mathrm{0,2}}{\overset{2N-2}{\mathrm{\Σ}}}v\left(\frac{2n+3}{4}T\right)]$

$=\frac{1}{N}\left\{\underset{n=\mathrm{0,2}}{\overset{2N-2}{\mathrm{\Σ}}}\right[v_e\left(\frac{2n+1}{4}T\right)+v_z\left(\frac{2n+1}{4}T\right)+v_i\left(\frac{2n+1}{4}T\right)+v_n\left(\frac{2n+1}{4}T\right)]-\underset{m=\mathrm{0,2}}{\overset{2N-2}{\mathrm{\Σ}}}[v_z\left(\frac{2n+3}{4}T\right)+v_i\left(\frac{2n+3}{4}T\right)+v_n\left(\frac{2n+3}{4}T\right)\left]\right\}$

$=\frac{1}{N}\underset{n=\mathrm{0,2}}{\overset{2N-2}{\mathrm{\Σ}}}{v}_e\left(\frac{2n+1}{4}T\right)+\frac{1}{N}\underset{n=\mathrm{0,2}}{\overset{2N-2}{\mathrm{\Σ}}}[v_z\left(\frac{2n+1}{4}T\right)-v_z\left(\frac{2n+3}{4}T\right)]+\frac{1}{N}\underset{n=\mathrm{0,2}}{\overset{2N-2}{\mathrm{\Σ}}}\left[v_i\left(\frac{2n+1}{4}T\right){-v}_i\left(\frac{2n+3}{4}T\right)\right]+\frac{1}{N}\underset{n=\mathrm{0,2}}{\overset{2N-2}{\mathrm{\Σ}}}[v_n\left(\frac{2n+1}{4}T\right)-v_n\left(\frac{2n+3}{4}T\right)]$

(5) drift about with the slow variation of the environmental baselines such as temperature owing to the circuit zero-point voltage, and T is very little, N is very large, so

$\frac{1}{N}\underset{n=\mathrm{0,2}}{\overset{2N-2}{\mathrm{\Σ}}}[v_z\left(\frac{2n+1}{4}T\right)-v_z\left(\frac{2n+3}{4}T\right)]\≈0$

(6) because general environment is disturbed as low frequency or intermediate frequency disturb, and in the short time, environmental interference voltage can be considered DC voltage at the utmost point of N measuring period, so

$\frac{1}{N}\underset{n=\mathrm{0,2}}{\overset{2N-2}{\mathrm{\Σ}}}[v_i\left(\frac{2n+1}{4}T\right)-v_i\left(\frac{2n+3}{4}T\right)]\≈0$

(7) because circuit noise is a stationary stochastic process, and its amplitude of any moment and phase place all are at random, so noise voltage will be cancelled each other within N measuring period, the voltage of not offsetting fully also doubly can be ignored because dwindling N, namely

$\frac{1}{N}\underset{n=\mathrm{0,2}}{\overset{2N-2}{\mathrm{\Σ}}}[v_n\left(\frac{2n+1}{4}T\right)-v_n\left(\frac{2n+3}{4}T\right)]\≈0$

(8) comprehensive (4), (5), (6) and (7) get:

Be the impact that interference and noise were eliminated or greatly reduced to result of calculation, prove that above-mentioned metering circuit has larger noise and improves ratio and higher measuring accuracy.

In sum, measurement mechanism provided by the invention has anti-interference strong with the noise ability, the characteristics that measuring accuracy is high; Owing to adopted the microprocessor of the peripheral hardwares such as timer, analog to digital converter integrated, simplified circuit, improved reliability; In addition, compare with similar other high-precision measurement circuit, the circuit component that the present invention comprises, common, cheap, the negligible amounts of chip kind, thereby implementation cost is lower.

For measurement mechanism provided by the invention further is described, now measurement mechanism provided by the invention is applied in the optical fiber freezing sensor, as shown in Figure 5, concrete details are as follows:

Use the output signal of this passive sensor of measurement mechanism measuring optical fiber freezing sensor; The square-wave signal VDrive access driving circuit of microprocessor output; Output port Sensor+, the Sensor-of driving circuit provides exciting current for the light emitting diode of optical fiber freezing sensor; The output of the phototriode of optical fiber freezing sensor is linked into input port In+, the In-of amplifying circuit; The voltage acquisition port V1 of the output V1 access microprocessor of amplifying circuit; The analysis processing result of microprocessor outputs to Computer display, record by serial port RXD, TXD.Microprocessor utilizes the square-wave signal of the comparing unit generation constant frequency of timer internal, and exports from the IO port; Driving circuit receives output drive square wave behind the square wave that microprocessor produces; The light emitting diode conducting of the large current excitation optical fiber freezing sensor of square wave and luminous, make the optical fiber freezing sensor work in foment, the little electric current of square wave makes the light emitting diode cut-off of optical fiber freezing sensor, make the optical fiber freezing sensor work in nonexcited state, namely the optical fiber freezing sensor will be between foment and nonexcited state switch operating state periodically; Amplifying circuit is enlarged into analog voltage signal with the voltage signal of the phototriode output of optical fiber freezing sensor; This analog voltage signal is converted to digital signal by the analog to digital converter of microprocessor internal; Microprocessor calculates first the difference of the optical fiber freezing sensor different digital signal that moment analog to digital converter obtains in the middle of same excitation square-wave cycle underexcitation state and nonexcited state, calculate the mean value of these differences in a period of time that comprises many cycles, this result of calculation is as the output signal of optical fiber freezing sensor again; The output signal of optical fiber freezing sensor is exported to computing machine by the serial communication interface of microprocessor internal and is made further analyzing and processing.Adopt above-mentioned measurement mechanism that the output signal of optical fiber freezing sensor is measured, measuring accuracy is high, simple and reliable and cost is low.

The present invention also provides a kind of signal detection system, comprising: the passive sensor 1, measurement mechanism 2 and the computing machine 3 that connect successively; Wherein passive sensor 1 is used for collection signal, and measurement mechanism 2 is used for the signal of passive sensor 1 output is measured, and computing machine 3 carries out analyzing and processing with the signal of measurement mechanism 2 outputs.Owing to adopted above-mentioned measurement mechanism 2 so that the measuring accuracy of this signal detection system is high, measuring error is little.

Those skilled in the art will readily understand; the above only is preferred embodiment of the present invention; not in order to limiting the present invention, all any modifications of doing within the spirit and principles in the present invention, be equal to and replace and improvement etc., all should be included within protection scope of the present invention.

Claims (9)

1. a measurement mechanism that is used for measuring the passive sensor output signal is characterized in that, comprises amplifying circuit, driving circuit and microprocessor;

Described microprocessor comprises timer, analog to digital converter and serial communication interface;

The input end of described amplifying circuit is connected with passive sensor, and the output terminal of described amplifying circuit is connected with described analog to digital converter; The input end of described driving circuit is connected with described timer, and the output terminal of described driving circuit is connected with described passive sensor; Described serial communication interface is connected with the computing machine of outside;

Described driving circuit according to the square-wave signal output drive voltage of described microprocessor output or electric current and so that described passive sensor between foment and nonexcited state, periodically work; Described amplifying circuit is enlarged into analog voltage signal with the electric signal of described passive sensor output; Described analog to digital converter is converted to digital signal with described analog voltage signal; Described microprocessor is asked poor and average computation with the digital signal that constantly obtains in the middle of two kinds of duties of described passive sensor in a plurality of cycles, and result of calculation is exported to Computer Processing as the output signal of described passive sensor and by described serial communication interface.

2. measurement mechanism as claimed in claim 1 is characterized in that, described passive sensor is thermistor, voltage dependent resistor (VDR), humicap or optical fiber freezing sensor.

3. measurement mechanism as claimed in claim 1 is characterized in that, described microprocessor is single-chip microcomputer or dsp chip.

4. measurement mechanism as claimed in claim 1 is characterized in that, described driving circuit comprises:

The first resistance, the first electric capacity, the first switching tube;

One end of described the first resistance is as the output head anode of described driving circuit, the other end connection+5V voltage of described the first resistance;

One end of described the first electric capacity is connected to described+5V voltage, the other end ground connection of described the first electric capacity;

The control end of described the first switching tube is as the input end of described driving circuit, and the first end of described the first switching tube is as the negative pole of output end of described driving circuit, the second end ground connection of described the first switching tube; The control end of described the first switching tube is controlled the conducting between its first end and the second end.

5. measurement mechanism as claimed in claim 4, it is characterized in that, described the first switching tube is triode, the base stage of described triode is as the control end of described the first switching tube, the collector of described triode is as the first end of described the first switching tube, and the emitter of described triode is as the second end of described the first switching tube.

6. measurement mechanism as claimed in claim 1 is characterized in that, described amplifying circuit comprises: the second resistance, the 3rd resistance, the second electric capacity, the 3rd electric capacity, amplifier, the first one-way conduction element, the second one-way conduction element;

Described amplifier comprises 8 ports, the 1st port is connected to the 8th port by the second resistance and the 3rd resistance successively, the 2nd port is as the input cathode of described amplifying circuit, the 3rd port is as the input anode of described amplifying circuit, and the 4th port connects-12V voltage, and the 4th port is also by the 3rd capacity earth, the 5th port ground connection, the 6th port is as the output terminal of described amplifying circuit, and the 7th port connection+12V voltage, the 7th port are also by described the second capacity earth;

Described the first one-way conduction element and described the second one-way conduction element be connected in turn+3.3V voltage and ground between, described the first one-way conduction element and described the second one-way conduction element be connected in series the 6th port that end is connected to described amplifier.

7. measurement mechanism as claimed in claim 6 is characterized in that, described the first one-way conduction element is the first diode, the negative electrode connection+3.3V voltage of described the first diode, and the anodic bonding of described the first diode is to the 6th port of described amplifier.

8. measurement mechanism as claimed in claim 6 is characterized in that, described the second one-way conduction element is the second diode, and the negative electrode of described the second diode is connected to the 6th port of described amplifier, the plus earth of described the second diode.

9. a signal detection system comprises the passive sensor, measurement mechanism and the computing machine that connect successively; Described measurement mechanism is exported to Computer Processing with the output signal of described passive sensor; It is characterized in that described measurement mechanism is each described measurement mechanism of claim 1-8.

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