CN104807481A - Triangular wave excited impedance type sensor measuring circuit - Google Patents

Abstract

The invention discloses a triangular wave excited impedance type sensor measuring circuit and relates to the field of impedance measurement. The triangular wave excited impedance type sensor measuring circuit comprises a microcontroller; the microcontroller controls a digital analog converter to output triangular wave voltage signals with symmetrical positive and negative periods; the triangular wave voltage signals are converted to be triangular wave current signals through a voltage and current converter; the triangular wave current signals excite an impedance type sensor to generate voltage signals; the voltage signals are input to the digital analog converter after being amplified through an amplifier; the digital analog converter input a conversion result to a microcontroller; the microcontroller results of accumulated sum and subtract of respective data of the positive periods and negative periods of the triangular waves are proportional to output of the impedance type sensor through the microcontroller and then the impedance type sensor is calculated. The triangular wave excited impedance type sensor measuring circuit reduces complexity of a constant flow source circuit and a follow-up measuring circuit and improves the accuracy of Wheatstone bridge measurement.

Description

A kind of impedance based sensor metering circuit of triangular wave excitation

Technical field

The present invention relates to impedance based sensor fields of measurement, particularly relate to the impedance based sensor metering circuit of a kind of triangular wave excitation.

Background technology

Sensor is widely used in all trades and professions, and wherein impedance based sensor applies a most general class sensor, such as: thermistor, voltage dependent resistor (VDR) and capacitive transducer etc.In various impedance based sensor measuring method, need high-precision sinusoidal wave constant current source excitation impedance type sensor, but produce stable and sinusoidal signal amplitude and frequency accurately circuit is complicated and expensive, follow-up metering circuit is complexity and expensive equally.Itself is complicated with subsequent conditioning circuit, cost is high.

Summary of the invention

The invention provides the impedance based sensor metering circuit of a kind of triangular wave excitation, present invention reduces the complexity of constant-current source circuit and follow-up metering circuit, improve the precision that impedance based sensor is measured, described below:

An impedance based sensor metering circuit for triangular wave excitation, comprising: microcontroller, described impedance based sensor metering circuit also comprises: the digital to analog converter be connected with described microcontroller, analog to digital converter; Described digital to analog converter connects voltage current adapter, is also provided with amplifier between described voltage current adapter and described analog to digital converter;

Digital to analog converter described in described microprocessor controls exports the triangle wave voltage signal of positive and negative periodic symmetry, described triangle wave voltage signal converts triangular current signal to through described voltage current adapter, and described triangular current signal excitation impedance type sensor produces voltage signal;

Described voltage signal is input to described analog to digital converter after amplifying via described amplifier, and transformation result is input to described microcontroller by described analog to digital converter;

Described microcontroller by the positive and negative semiperiod of triangular wave separately the cumulative sum of data subtract each other the result obtained and be namely proportional to impedance based sensor, calculate described impedance based sensor, and then obtain the physical quantity measured by described impedance based sensor.

Another embodiment, a kind of impedance based sensor metering circuit of triangular wave excitation, comprising: microcontroller, described impedance based sensor metering circuit also comprises: the current D-A conveter be connected with described microcontroller, analog to digital converter; Also amplifier is provided with between described current D-A conveter and described analog to digital converter;

Current D-A conveter described in described microprocessor controls exports the triangular current differential wave of positive and negative periodic symmetry, and described triangular current differential wave excitation impedance type sensor produces voltage signal;

Described voltage signal is input to described analog to digital converter after amplifying via described amplifier, and transformation result is input to described microcontroller by described analog to digital converter;

Described microcontroller by the positive and negative semiperiod of triangular wave separately the cumulative sum of data subtract each other the result obtained and be namely proportional to impedance based sensor, calculate described impedance based sensor, and then obtain the physical quantity measured by described impedance based sensor.

Another embodiment, a kind of impedance based sensor metering circuit of triangular wave excitation, comprising: microcontroller, described impedance based sensor metering circuit also comprises: the integrator be connected with described microcontroller, analog to digital converter; Described integrator connects voltage current adapter, is also provided with amplifier between described voltage current adapter and described analog to digital converter;

It is the two-way square wave voltage signal of 50% that described microcontroller exports anti-phase, dutycycle each other, described two-way square wave voltage signal converts two-way triangle wave voltage signal to through described integrator, described two-way triangle wave voltage signal is merged into differential triangular current signal through described voltage current adapter again, and described triangular current signal excitation impedance type sensor produces voltage signal;

Described voltage signal is input to described analog to digital converter after amplifying via described amplifier, and transformation result is input to described microcontroller by described analog to digital converter;

Described microcontroller by the positive and negative semiperiod of triangular wave separately the cumulative sum of data subtract each other the result obtained and be namely proportional to impedance based sensor, calculate described impedance based sensor, and then obtain the physical quantity measured by described impedance based sensor.

It is the two-way square wave voltage signal of 50% that first general mouthful of line of described microcontroller and second general mouthful of line export anti-phase, dutycycle each other.

Described integrator is made up of the first resistance, the second resistance and electric capacity.

The beneficial effect of technical scheme provided by the invention is: the present invention by microcontroller by the positive and negative semiperiod of triangular wave separately the cumulative sum of data subtract each other the result obtained and be namely proportional to impedance based sensor, calculate the value of impedance based sensor, and then obtain the physical quantity measured by sensor; The present invention not only can simplify sinusoidal constant current source exciting circuit itself required in routine measurement, can also simplify follow-up metering circuit, and significantly improve the measuring accuracy of impedance transducer.

Accompanying drawing explanation

Fig. 1 is the structural representation of the impedance based sensor metering circuit of a kind of triangular wave excitation of embodiment 1;

Fig. 2 is the triangle wave voltage signal schematic representation of embodiment 1;

Fig. 3 is the structural representation of the impedance based sensor metering circuit of a kind of triangular wave excitation of embodiment 2;

Fig. 4 is the triangular current signal schematic representation of embodiment 2;

Fig. 5 is the structural representation of the impedance based sensor metering circuit of a kind of triangular wave excitation of embodiment 3;

Fig. 6 is the square wave voltage signal schematic diagram of embodiment 3.

In accompanying drawing, the list of parts representated by each label is as follows:

MCU: microcontroller; DAC: digital to analog converter;

VCC: voltage current adapter; A: amplifier;

ADC: analog to digital converter; Z _x: impedance based sensor;

IDAC: current D-A conveter; GPIO ₁: first general mouthful of line;

GPIO ₂: second general mouthful of line; R ₁: the first resistance;

R ₂: the second resistance; C ₁: electric capacity;

I _i: triangular current signal; V _i: voltage signal.

Embodiment

For making the object, technical solutions and advantages of the present invention clearly, below embodiment of the present invention is described further in detail.

Embodiment 1

See Fig. 1, a kind of impedance based sensor metering circuit of triangular wave excitation, comprising: microcontroller, digital to analog converter DAC, voltage current adapter VCC, amplifier A, analog to digital converter ADC;

Microcontroller domination number weighted-voltage D/A converter DAC exports the triangle wave voltage signal of positive and negative periodic symmetry as shown in Figure 2, and triangle wave voltage signal converts triangular current signal I to through voltage current adapter VCC _i, triangular current signal I _iexcitation impedance type sensor Z _x, produce voltage signal V _i=I _iz _xvoltage signal is input to analog to digital converter ADC after amplifying via amplifier A, transformation result is input to microcontroller by analog to digital converter ADC, microcontroller by the positive and negative semiperiod of triangular wave separately the cumulative sum of data subtract each other the result obtained and be namely proportional to impedance based sensor Z _x, can impedance based sensor Z be calculated _x, and then obtain impedance based sensor Z _xmeasured physical quantity x.

That is, by the sampled value v of the positive half period of each triangular wave in certain hour (an integer triangular wave cycle) _iadd up and obtain cumulative sum, the sampled value v of the negative half period of each triangular wave _jadd up and obtain cumulative sum, these two cumulative sums are subtracted each other, and the result (the actual area for triangular wave) obtained is proportional to impedance based sensor Z _x, can impedance based sensor Z be calculated _x, and then obtain impedance based sensor Z _xmeasured physical quantity x, can derive as follows:

Calculate the area of triangular wave for one-period, each periodic sampling 2k time, add up for k time after front k cumulative sum: the mean value of sampled value is within a triangular wave cycle:

$\stackrel{\‾}{V}=\frac{1}{2k}\underset{1}{\overset{2k}{\mathrm{\Σ}}}v---\left(1\right)$

At the area of a triangular wave cycle interior triangular be:

$S=\underset{1}{\overset{2k}{\mathrm{\Σ}}}|v-\stackrel{\‾}{V}|---\left(2\right)$

When positive half period sampling, sampled value v is v _i; When negative half period sampling, sampled value v is v _j.

That is, $S=\underset{1}{\overset{k}{\mathrm{\Σ}}}(v_i-\stackrel{\‾}{V})+\underset{k+1}{\overset{2k}{\mathrm{\Σ}}}(\stackrel{\‾}{V}-v_j)---\left(3\right)$

Last item: time calculate positive half period, latter one: calculate negative half-cycle.

$S=\underset{1}{\overset{k}{\mathrm{\Σ}}}{v}_i+\underset{k+1}{\overset{2k}{\mathrm{\Σ}}}(-v_j)---\left(4\right)$

Two, attention front and back identical value, but and v _j> 0, so

$S=\underset{1}{\overset{k}{\mathrm{\Σ}}}{v}_i-\underset{k+1}{\overset{2k}{\mathrm{\Σ}}}{v}_j---\left(5\right)$

To amplitude be x be sampled value, if uniform sampling N (>>1) puts and is averaged within the regular hour, the mean value obtained is

$\stackrel{\‾}{x}=\frac{1}{N}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}\left[x_i\right]=\frac{1}{N}N\left(\right[x]+\mathrm{\Δ}{x}_i)=\left[x\right]+\mathrm{\Δ}{x}_i---\left(6\right)$

Wherein, [x] is that analog to digital converter quantizes x, is also the positive integer that round off rounding obtains.X _ithe amplitude of i-th, [x _i] be that analog to digital converter is to x _iquantizing, is also the positive integer that round off rounding obtains.

(6) formula shows, the signal sampling one being compared to " totally " is repeatedly averaged, and can not improve its precision, and the error of the mean value obtained is identical with the error of unitary sampling, is Δ x _i.

If to amplitude be x be sampled sawtooth wave, within the regular hour, uniform sampling N (>>1) puts and is averaged equally, and the mean value obtained is

$\stackrel{\‾}{x}=\frac{1}{N}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}\left[x_i\right]=\frac{1}{N}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}[m_i+\mathrm{\Δ}{x}_i]---\left(7\right)$

Wherein, x _i=m _i+ Δ x _i, m _i=[x _i].Also be m _ithat rounding obtains positive integer, and Δ x _iit is " at random " error of losing after being rounded.

(7) formula can utilize arithmetic series sum formula to obtain further:

$\begin{array}{c}\stackrel{\‾}{x}=\frac{1}{N}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{m}_i+\frac{1}{N}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}\mathrm{\Δ}{x}_i=\frac{1}{N}\frac{1}{2}(0+[x\left]\right)N+\frac{1}{N}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}\mathrm{\Δ}{x}_i\\ =\frac{1}{2}\left[x\right]+\frac{1}{N}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}\mathrm{\Δ}{x}_i\end{array}---\left(8\right)$

(8) the last item in formula is the value after quantizing, although less than the result of (6) formula half, according to theory of errors, the precision of data does not change because being multiplied by a fixing non-zero constant.But be the random number of zero-mean in one next, compare will reduce in (6) formula doubly, therefore, the effect of the precision that can be improved equally after over-sampling is carried out to sawtooth wave or triangular wave pumping signal, and do not need another external high-frequency disturbing signal.

The embodiment of the present invention is to the model of each device except doing specified otherwise, and the model of other devices does not limit, as long as can complete the device of above-mentioned functions.

Embodiment 2

See Fig. 3, a kind of impedance based sensor metering circuit of triangular wave excitation, comprising: microcontroller, current D-A conveter IDAC, amplifier A, analog to digital converter ADC;

Microcontroller controls the triangular current differential wave I that current D-A conveter IDAC exports positive and negative periodic symmetry as shown in Figure 4 _i, triangular current differential wave I _iexcitation impedance type sensor Z _x, produce voltage signal V _i=I _iz _xvoltage signal is input to analog to digital converter ADC after amplifying via amplifier A, transformation result is input to microcontroller by analog to digital converter ADC, microcontroller by the positive and negative semiperiod of triangular wave separately the cumulative sum of data subtract each other the result obtained and be namely proportional to impedance based sensor Z _x, can impedance based sensor Z be calculated _x, and then obtain impedance based sensor Z _xmeasured physical quantity x.

Wherein, the microcontroller in the present embodiment by the positive and negative semiperiod of triangular wave separately the cumulative sum of data subtract each other the result obtained and be namely proportional to impedance based sensor Z _xdetailed operating procedures identical with embodiment 1, therefore not to repeat here.

The embodiment of the present invention is to the model of each device except doing specified otherwise, and the model of other devices does not limit, as long as can complete the device of above-mentioned functions.

Embodiment 3

See Fig. 5, a kind of impedance based sensor metering circuit of triangular wave excitation, comprising: microcontroller, integrator, voltage current adapter VCC, amplifier A, analog to digital converter ADC;

First general mouthful of line GPIO of microcontroller ₁with second general mouthful of line GPIO ₂export the two-way square wave voltage signal that anti-phase each other, dutycycle is as shown in Figure 6 50%, two-way square wave voltage signal through integrator (by the first resistance R ₁, the second resistance R ₂with electric capacity C ₁composition, wherein, integrating circuit can convert square-wave signal to triangular signal, and has time delay and phase shift effect) convert two-way triangle wave voltage signal to, two-way triangle wave voltage signal is merged into differential triangular current signal I through voltage current adapter VCC again _i, triangular current signal I _iexcitation impedance type sensor Z _x, produce voltage signal V _i=I _iz _xvoltage signal is input to analog to digital converter ADC after amplifying via amplifier A, transformation result is input to microcontroller by analog to digital converter ADC, microcontroller by the positive and negative semiperiod of triangular wave separately the cumulative sum of data subtract each other the result obtained and be namely proportional to impedance based sensor Z _x, can impedance based sensor Z be calculated _x, and then obtain impedance based sensor Z _xmeasured physical quantity x.

Wherein, the microcontroller in the present embodiment by the positive and negative semiperiod of triangular wave separately the cumulative sum of data subtract each other the result obtained and be namely proportional to impedance based sensor Z _xdetailed operating procedures identical with embodiment 1, therefore not to repeat here.

The embodiment of the present invention is to the model of each device except doing specified otherwise, and the model of other devices does not limit, as long as can complete the device of above-mentioned functions.

It will be appreciated by those skilled in the art that accompanying drawing is the schematic diagram of a preferred embodiment, the invention described above embodiment sequence number, just to describing, does not represent the quality of embodiment.

The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, within the spirit and principles in the present invention all, any amendment done, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (5)

1. an impedance based sensor metering circuit for triangular wave excitation, comprising: microcontroller, it is characterized in that, described impedance based sensor metering circuit also comprises: the digital to analog converter be connected with described microcontroller, analog to digital converter; Described digital to analog converter connects voltage current adapter, is also provided with amplifier between described voltage current adapter and described analog to digital converter;

Digital to analog converter described in described microprocessor controls exports the triangle wave voltage signal of positive and negative periodic symmetry, described triangle wave voltage signal converts triangular current signal to through described voltage current adapter, and described triangular current signal excitation impedance type sensor produces voltage signal;

Described voltage signal is input to described analog to digital converter after amplifying via described amplifier, and transformation result is input to described microcontroller by described analog to digital converter;

Described microcontroller by the positive and negative semiperiod of triangular wave separately the cumulative sum of data subtract each other the result obtained and be namely proportional to impedance based sensor, calculate described impedance based sensor, and then obtain the physical quantity measured by described impedance based sensor.

2. an impedance based sensor metering circuit for triangular wave excitation, comprising: microcontroller, it is characterized in that, described impedance based sensor metering circuit also comprises: the current D-A conveter be connected with described microcontroller, analog to digital converter; Also amplifier is provided with between described current D-A conveter and described analog to digital converter;

Current D-A conveter described in described microprocessor controls exports the triangular current differential wave of positive and negative periodic symmetry, and described triangular current differential wave excitation impedance type sensor produces voltage signal;

Described voltage signal is input to described analog to digital converter after amplifying via described amplifier, and transformation result is input to described microcontroller by described analog to digital converter;

Described microcontroller by the positive and negative semiperiod of triangular wave separately the cumulative sum of data subtract each other the result obtained and be namely proportional to impedance based sensor, calculate described impedance based sensor, and then obtain the physical quantity measured by described impedance based sensor.

3. an impedance based sensor metering circuit for triangular wave excitation, comprising: microcontroller, it is characterized in that, described impedance based sensor metering circuit also comprises: the integrator be connected with described microcontroller, analog to digital converter; Described integrator connects voltage current adapter, is also provided with amplifier between described voltage current adapter and described analog to digital converter;

It is the two-way square wave voltage signal of 50% that described microcontroller exports anti-phase, dutycycle each other, described two-way square wave voltage signal converts two-way triangle wave voltage signal to through described integrator, described two-way triangle wave voltage signal is merged into differential triangular current signal through described voltage current adapter again, and described triangular current signal excitation impedance type sensor produces voltage signal;

Described voltage signal is input to described analog to digital converter after amplifying via described amplifier, and transformation result is input to described microcontroller by described analog to digital converter;

Described microcontroller by the positive and negative semiperiod of triangular wave separately the cumulative sum of data subtract each other the result obtained and be namely proportional to impedance based sensor, calculate described impedance based sensor, and then obtain the physical quantity measured by described impedance based sensor.

4. the impedance based sensor metering circuit of a kind of triangular wave excitation according to claim 3, is characterized in that, it is the two-way square wave voltage signal of 50% that first general mouthful of line of described microcontroller and second general mouthful of line export anti-phase, dutycycle each other.

5. the impedance based sensor metering circuit of a kind of triangular wave excitation according to claim 3, it is characterized in that, described integrator is made up of the first resistance, the second resistance and electric capacity.