CN105380647A - Weak dynamic impedance detection device and method based on four-electrode half-bridge method - Google Patents
Weak dynamic impedance detection device and method based on four-electrode half-bridge method Download PDFInfo
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Abstract
The invention discloses a weak dynamic impedance detection device and method based on a four-electrode half-bridge method. A half-arm automatic balanced bridge circuit is formed by a digital potentiometer and a bioimpedance device; a programmable amplifying circuit is formed by two instrumentation amplifiers and one programmable instrumentation amplifier, output of one instrumentation amplifier is partial voltage V1 of the digital potentiometer, output of the other instrumentation amplifier is partial voltage V2 of the bioimpedance device, and output of the programmable instrumentation amplifier is the difference value between V1 and V2; voltage amplitude of weak dynamic impedance change signals demodulated by a fast digital phase locking circuit based on oversampling serves as negative feedback, an automatic balance adjusting circuit controls the tapping position of the digital potentiometer until the demodulated voltage amplitude is within the threshold value range, and the automatic balance adjusting circuit enters a balanced state. Dynamic impedance detection based on the four-electrode half-bridge method is achieved, and the weak dynamic impedance detection device has the advantages of high accuracy and sensitivity, a large dynamic range, easy realization and real-time continuous measurement.
Description
Technical field
The present invention relates to motional impedance detection field, particularly relate to a kind of faint motional impedance checkout gear based on four electrode half-bridge methods and method thereof.
Background technology
Bioelectrical impedance analysis is a kind of non-invasive, and cost is low, conventional somatometry and clinical state appraisal procedure.Along with the development increasingly of biological impedance technology is with ripe, biological impedance is applied to and clinically becomes possibility.Bio-impedance can be divided into static basis impedance and faint motional impedance two parts.More physiologic information is often carried in faint motional impedance change, and therefore the real-time continuous of faint motional impedance variable quantity is monitored as clinical practice provides possibility.In the measurement of faint motional impedance, the impact of deduction static basis impedance is crucial.
Inventor is realizing finding in process of the present invention, existing impedance measurement method, usually static impedance and faint motional impedance are gathered in gatherer process simultaneously, and carry out the amplification of same degree, for and the measurement of faint motional impedance variable quantity cause certain difficulty.Simultaneously larger static basis impedance can introduce individual difference, clinically causes certain difficulty for impedance measurement means are applied to.
Summary of the invention
The invention provides a kind of faint motional impedance checkout gear based on four electrode half-bridge methods and method thereof, the present invention has that precision is high, highly sensitive, dynamic range is large, the advantage such as low in energy consumption and with low cost, monitoring for a long time continuously can be carried out to comparatively faint motional impedance variable quantity, described below:
Based on a faint motional impedance checkout gear for four electrode half-bridge methods, comprising: excitation constant-current source, also comprises:
Half arm self-balancing bridge circuit circuit, is made up of jointly digital regulation resistance and bio-impedance;
Pga circuit is made up of jointly 2 instrumentation amplifiers and a programmable instrument amplifier, and the output of an instrumentation amplifier is the dividing potential drop V of digital regulation resistance
1, the output of another instrumentation amplifier is the dividing potential drop V of bio-impedance
2, the output of programmable instrument amplifier is V
1and V
2difference;
Automatic Balance Regulation circuit, according to the voltage magnitude of the faint motional impedance variable signal out of the fast digital phase lock circuitry demodulation based on over-sampling as negative feedback, the tap position of control figure potentiometer, until the voltage magnitude demodulated enters within threshold value, then Automatic Balance Regulation circuit enters balance dress state.
Described excitation constant-current source is high frequency sinusoidal constant current supply pumping signal.
Described four electrode configuration circuits are made up of four electrodes, and the mode adopting exciting electrode and measurement electrode to separate is configured.
Described programmable instrument amplifier is for carrying out amplification in various degree to static basis impedance and faint dynamic change impedance.
Based on a faint motional impedance detection method for four electrode half-bridge methods, described method is a kind of autobalance half-bridge method, said method comprising the steps of:
Digital regulation resistance is expressed as R
s, tested bio-impedance is expressed as R
z;
After high frequency sinusoidal current excitation, R
sthe output voltage of both end voltage after an instrumentation amplifier represents for V
1, R
zthe output voltage of two ends after another instrumentation amplifier represents for V
2;
V
1with V
2output voltage after programmable instrument amplifier represents for V
out, V
outdigital signal is converted to by analog-digital converter;
By carrying out solution harmonic average filtering based on the fast digital of over-sampling is phase-locked to digital signal, obtain the voltage magnitude of tested impedance;
The voltage magnitude of the tested bio-impedance that fast digital demodulation of phase locking obtains, as negative-feedback signal, is adjusted by the tap position of self-balancing bridge circuit to digital regulation resistance;
If the absolute value of deviation is greater than deviation threshold, then recalculate amplitude and deviation, until the absolute value of deviation is less than deviation threshold, then complete the adjustment of bridge balance.
The beneficial effect of technical scheme provided by the invention is: the present invention removes the impact of contact impedance by four electrode method, adopt autobalance half-bridge method to reach the object of the larger static basis impedance of deduction simultaneously, and by the amplification that programmable instrument amplifier carries out in various degree to static basis impedance and motional impedance variable quantity, then the data after ADC sampling are carried out to the quick phase locked algorithm based on over-sampling thus demodulated faint impedance variation amount.The present invention can carry out detecting continuously, for a long time to faint motional impedance variable quantity, and has the advantages that precision is high, highly sensitive, dynamic range is large, with low cost, low in energy consumption, volume is little, has higher using value.
Accompanying drawing explanation
Fig. 1 is the structural representation of a kind of faint motional impedance checkout gear based on four electrode half-bridge methods provided by the invention;
Fig. 2 is the circuit diagram detected based on the faint motional impedance of four electrode half-bridge methods provided by the invention;
Fig. 3 is distribution of electrodes figure provided by the invention;
Fig. 4 is flow chart electric bridge being carried out to the adjustment of amplitude autobalance;
Fig. 5 is experimental waveform figure.
In accompanying drawing, being listed as follows of each parts:
1: excitation constant-current source; 2: half arm self-balancing bridge circuit circuit;
3: pga circuit; 4: fast digital phase lock circuitry;
5: Automatic Balance Regulation circuit; 6: four electrode configuration circuits.
Detailed description of the invention
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
A kind of faint motional impedance checkout gear based on four electrode half-bridge methods, see Fig. 1 and Fig. 2, this checkout gear comprises: excitation constant-current source 1, half arm self-balancing bridge circuit circuit 2, pga circuit 3, fast digital phase lock circuitry 4, Automatic Balance Regulation circuit 5 and four electrode configuration circuits 6 based on over-sampling.
Wherein, constant-current source 1 is encouraged to be the sinusoidal constant-current source pumping signal of altofrequency.
The bridge arm of half arm self-balancing bridge circuit circuit 2 is made up of jointly digital regulation resistance and bio-impedance, the object of half arm self-balancing bridge circuit circuit 2 is the impedances of deduction static basis, eliminate the individual variation that it causes, extract faint motional impedance component thus improve dynamic range and certainty of measurement.
See Fig. 2, pga circuit 3 is formed jointly primarily of 2 instrumentation amplifiers and a programmable instrument amplifier, and wherein, the output of instrumentation amplifier A1 is the dividing potential drop V of digital regulation resistance
1, the output of instrumentation amplifier A2 is the dividing potential drop V of bio-impedance
2, the output of programmable instrument amplifier A3 is V
1and V
2difference V
out, wherein the major function of programmable instrument amplifier A3 is the amplification carrying out in various degree to static basis impedance and faint dynamic change impedance.
Automatic Balance Regulation circuit 5, according to the voltage magnitude of the faint motional impedance variable signal out of fast digital phase lock circuitry 4 demodulation based on over-sampling as negative feedback, the tap position of control figure potentiometer, until the voltage magnitude of demodulation faint motional impedance variable signal out enters within default threshold value, then Automatic Balance Regulation circuit 5 enters equilibrium state.
During specific implementation, high frequency sinusoidal constant current supply pumping signal can be produced by microprocessor; Fast digital phase lock circuitry 4 based on over-sampling also can be realized by microprocessor; Pga circuit 3 and Automatic Balance Regulation circuit 5 also all can be realized by micro-process.
Four electrode configuration circuits 6 are made up of four electrodes, and the mode adopting exciting electrode and measurement electrode to separate is configured.Its major function eliminates the interference of contact impedance introducing, and then improve the certainty of measurement of system.See Fig. 2 and Fig. 3, four electrodes are respectively a, b, c and d, and wherein a, d are exciting electrode, and b, c are 2 measurement electrode.
Wherein, above-mentioned all microprocessors mentioned are same microprocessors, and this microprocessor is a kind of processor of high integrated Micro Energy Lose, with low cost, simple to operate.Microprocessor can adopt in MCU, ARM, DSP or FPGA any one.
Embodiment 2
Below in conjunction with concrete device model, the faint motional impedance checkout gear based on four electrode half-bridge methods in embodiment 1 is described further, refers to hereafter:
In the embodiment of the present invention, the microprocessor of employing is low-power microprocessor CY8C3866AXI; Analog-digital converter ADC is 11bit, and sample rate is 200Ksps, and over-sampling multiple is 4.
Amplifying circuit 3 comprises 2 instrumentation amplifier AD623, and the programmable instrument amplifier A3 that programmable gain amplifier on microprocessor used and amplifier are formed, after Automatic Balance Regulation circuit 5 reaches equilibrium state, the gain improving programmable amplifier, to the distortionless maximum gain of signal, now can demodulate faint motional impedance variable signal.Digital regulation resistance in Automatic Balance Regulation circuit 5 is specially the 20k digital regulation resistance AD5272 with 1024 taps.
Be 25000 based on the lower number of sampling points of average filter in the fast digital phase lock circuitry 4 of over-sampling, about 4
6-4
8between, so most-significant byte is carried in analog-digital converter ADC equivalence, the equivalent resolution of this checkout gear reaches 0.822 μ V/bit.Comparatively faint motional impedance variable quantity can be measured accurately.Self-balancing bridge circuit makes system signal noise ratio be significantly improved.
Embodiment 3
The ultimate principle realizing the faint motional impedance detection method of four electrode half-bridge methods is described below, in detail schematic diagram as shown in Figure 4, and first, the method is a kind of autobalance half-bridge method, also can be called elementary errors modulation method, and half arm modulation bridge is by digital regulation resistance R
swith bio-impedance R
zcommon formation.
101: microprocessor produces a road high frequency sinusoidal current excitation signal and is expressed as I (t), and its frequency configuration is 50kHz;
102: digital regulation resistance is expressed as R
s, tested bio-impedance is expressed as R
z;
103: after high frequency sinusoidal current excitation, R
sthe output voltage of both end voltage after instrumentation amplifier A1 represents for V
1, R
zthe output voltage of two ends after instrumentation amplifier A2 represents for V
2;
104:V
1with V
2output voltage after programmable instrument amplifier A3 represents for V
out, V
outdigital signal V is become with the sample rate conversion of 200Ksps by the analog-digital converter ADC in microprocessor
dout;
105: microprocessor is phase-locked to digital signal V by the fast digital based on over-sampling
doutcarry out solution harmonic average filtering, obtain the voltage magnitude of tested impedance;
106: the voltage magnitude of the tested bio-impedance that fast digital demodulation of phase locking obtains, as negative-feedback signal, is adjusted by the tap position of self-balancing bridge circuit to digital regulation resistance.
During specific implementation, according to four electrode allocation plans, exciting electrode and measurement electrode spaced apart, to ensure the interference eliminating contact impedance introducing, all there is exciting electrode measurement electrode at the two ends of impedance to be measured, and exciting electrode and measurement electrode interval are about 2.5cm.
In the embodiment of the present invention, the flow chart of specific implementation bridge balance adjustment, see Fig. 4, comprise: start to adjust, digital regulation resistance initial position is set, calculate the amplitude of digital signal, calculate amplitude and desired value deviation, calculate tap position by deviation and digital regulation resistance tap position, again calculation deviation are set, judge whether to reach the threshold range of deviation, complete the adjustment of bridge balance, the gain of programmable amplifier is improved after balance, program adjustment terminates, and starts to measure motional impedance variable signal.
Wherein, the condition starting to adjust is that human body keeps transfixion, system electrification, start-up routine.It is with the phase-locked fast V calculated based on over-sampling that amplitude balance regulates
doutsignal amplitude as negative-feedback signal, by the tap position of negative-feedback signal determination digital regulation resistance, make electric bridge reach poised state by adjusting the tap position of digital regulation resistance.
First, the initial position R of the tap of digital regulation resistance is set
s=0, calculate now digital signal V
doutsignal amplitude y, calculated the deviation e of amplitude y and adjustment aim value w by e=y-w, according to formula u
i=ke+u
0calculate the tap position u next time adjusting required digital regulation resistance
i, wherein k is for regulating proportionality coefficient, u
0for the initial position of digital regulation resistance, calculate u
iafter reset the tap position of digital regulation resistance, if the absolute value of deviation e is greater than the threshold value E0 of deviation, then need to recalculate amplitude y and deviation e, until the absolute value of deviation e is less than the threshold value E0 of deviation, then complete the adjustment of bridge balance, now, improve the gain of programmable instrument amplifier to distortionless maximum rating, i.e. gain k=max, program adjustment terminates, the signal V now exported
outbe faint motional impedance variable signal.
Wherein, k is scaling factor, is to be determined by the characteristic of whole device.
Wherein, adjustment aim value w is set to 20mV, arranges the threshold value E0=10mV of the deviation e of output amplitude y and adjustment aim value w, has judged whether that the adjusting condition of balanced adjustment is the threshold value E0 that the absolute value of deviation e is less than deviation.Adjust the scope of rear output signal y between w-E0 and w+E0.
Wherein, the scope that programmable instrument amplifier gain improves is 4 ~ 32 times.By the adjustment of above step, the bio-impedance value of minor variations can be made to be exaggerated and more easily to detect.
Embodiment 4
Be described in detail below in conjunction with the ultimate principle of concrete computing formula to the faint motional impedance measurement based on four electrode half-bridge methods in embodiment 3, refer to hereafter:
When the pumping signal that microprocessor produces is high-frequency current signal, can represent with formula (1):
I＝Asin(wt)+I
0(1)
Wherein, ω=2 π f is the angular frequency of pumping signal; I is excitation current source; T is time variable; A is the amplitude of ac current source; I
0for DC bias current.Wherein the output of instrumentation amplifier A1 is R
sboth end voltage, its expression formula is as shown in formula (2):
V
1＝IR
S＝R
S(Asin(wt)+I
0)＝AR
Ssin(wt)+I
0R
S(2)
Wherein the output of instrumentation amplifier A2 is bio-impedance R
zboth end voltage, its expression formula is as shown in formula (3):
V
2＝I(R
Z+ΔZ)＝(R
Z+ΔZ)(Asin(wt)+I
0)＝R
Z(Asin(wt)+I
0)+ΔZ(Asin(wt)+I
0)(3)
The output of programmable instrument amplifier A3 is V
1with V
2difference, its expression formula is as shown in formula (4):
V
out＝V
1-V
2＝(R
S-R
Z)(Asin(wt)+I
0)-ΔZ(Asin(wt)+I
0)(4)
Wherein, bio-impedance comprises: static basis impedance and dynamic change impedance two parts, R
zrepresent static basis impedance: Δ Z represents faint motional impedance variable quantity.
Want to measure faint motional impedance variable quantity, need the impact of deducting static basis impedance, thus improve signal to noise ratio, expand the dynamic range of signal.Wherein, digital regulation resistance R
smain Function be exactly the impact of deduction static basis impedance.
During specific implementation, when starting to adjust electric bridge, the multiple of all amplifiers is set to 1, the tap position of adjustment digital regulation resistance, until R
swith R
zapproximately equal.Now export as shown in formula (5):
V
out＝V
1-V
2＝-ΔZ(Asin(wt)+I
0)(5)
Simultaneously because Δ Z is minimum, thus export close to 0, so now the amplification of programmable instrument amplifier A3, close to balance, is adjusted to distortionless maximum rating by electric bridge, then output signal is the signal of faint motional impedance variable quantity.
Embodiment 5
Below in conjunction with concrete example, feasibility checking is carried out to the scheme in embodiment 1-4, described below:
To measure breathing, microprocessor used is the CY8C3866 of CYPRESS, excitation current source I used is generated by the IDAC on this microprocessor, frequency adopts 50kHz, half-bridge circuit adopts digital regulation resistance AD5272 and human body impedance to form, digital regulation resistance AD5272 used, and tap is 1024 taps, total resistance is 20k Ω, and the resolution of resistance is 19.5 Ω.Amplifier section is made up of 2 instrumentation amplifier AD623 and programmable instrument amplifier A3, and wherein programmable instrument amplifier A3 is made up of the programmable amplifier on microprocessor and operational amplifier and jointly forms.ADC sample rate on microprocessor used is set to 200ksps.Demodulating algorithm used is the quick phase locked algorithm of numeral based on over-sampling, and counting is 25000 points, and the sampling rate obtained after lower sampling is 8sps, acquisition per minute 480 points.
Fig. 5 is the respiratory waveform detected in 1 minute, and wherein abscissa is sampling number, and vertical coordinate is the output of system, and as shown in Figure 5, measured respiratory frequency is 16 times/min.
This faint motional impedance measuring method based on four electrode half-bridge methods eliminates individual variation by the impedance of deduction static basis, eliminate the interference that contact impedance is introduced, improve certainty of measurement, continuous real-time monitoring can be carried out to the faint motional impedance variable quantity of Different Individual, there is important clinical value.
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. based on a faint motional impedance checkout gear for four electrode half-bridge methods, comprising: excitation constant-current source, also comprises:
Half arm self-balancing bridge circuit circuit, is made up of jointly digital regulation resistance and bio-impedance;
Pga circuit is made up of jointly 2 instrumentation amplifiers and a programmable instrument amplifier, and the output of an instrumentation amplifier is the dividing potential drop V of digital regulation resistance
1, the output of another instrumentation amplifier is the dividing potential drop V of bio-impedance
2, the output of programmable instrument amplifier is V
1and V
2difference;
Automatic Balance Regulation circuit, according to the voltage magnitude of the faint motional impedance variable signal out of the fast digital phase lock circuitry demodulation based on over-sampling as negative feedback, the tap position of control figure potentiometer, until the voltage magnitude demodulated enters within threshold value, then Automatic Balance Regulation circuit enters poised state.
2. a kind of faint motional impedance checkout gear based on four electrode half-bridge methods according to claim 1, it is characterized in that, described excitation constant-current source is high frequency sinusoidal constant current supply pumping signal.
3. a kind of faint motional impedance checkout gear based on four electrode half-bridge methods according to claim 1, it is characterized in that, described four electrode configuration circuits are made up of four electrodes, and the mode adopting exciting electrode and measurement electrode to separate is configured.
4. a kind of faint motional impedance checkout gear based on four electrode half-bridge methods according to claim 1, is characterized in that, described programmable instrument amplifier is for carrying out amplification in various degree to static basis impedance and faint dynamic change impedance.
5. based on a faint motional impedance detection method for four electrode half-bridge methods, it is characterized in that, described method is a kind of autobalance half-bridge method, said method comprising the steps of:
Digital regulation resistance is expressed as R
s, tested bio-impedance is expressed as R
z;
After high frequency sinusoidal current excitation, R
sthe output voltage of both end voltage after an instrumentation amplifier represents for V
1, R
zthe output voltage of two ends after another instrumentation amplifier represents for V
2;
V
1with V
2output voltage after programmable instrument amplifier represents for V
out, V
outdigital signal is converted to by analog-digital converter;
By carrying out solution harmonic average filtering based on the fast digital of over-sampling is phase-locked to digital signal, obtain the voltage magnitude of tested impedance;
The voltage magnitude of the tested bio-impedance that fast digital demodulation of phase locking obtains, as negative-feedback signal, is adjusted by the tap position of self-balancing bridge circuit to digital regulation resistance;
If the absolute value of deviation is greater than deviation threshold, then recalculate amplitude and deviation, until the absolute value of deviation is less than deviation threshold, then complete the adjustment of bridge balance.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201510700478.XA CN105380647B (en) | 2015-10-26 | 2015-10-26 | A kind of faint motional impedance detection device and its method based on four electrode half-bridge methods |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201510700478.XA CN105380647B (en) | 2015-10-26 | 2015-10-26 | A kind of faint motional impedance detection device and its method based on four electrode half-bridge methods |
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| Publication Number | Publication Date |
|---|---|
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| CN105380647B CN105380647B (en) | 2018-12-25 |
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ID=55413858
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106175773A (en) * | 2016-07-11 | 2016-12-07 | 芯海科技（深圳）股份有限公司 | Hand held multiband impedance breath signal measures system and measuring method |
| CN106805948A (en) * | 2017-03-10 | 2017-06-09 | 安徽通灵仿生科技有限公司 | A kind of children use finger cot type remote diagnosis system |
| CN106901706A (en) * | 2017-03-10 | 2017-06-30 | 安徽通灵仿生科技有限公司 | A kind of children gloves formula remote diagnosis system |
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| US3750649A (en) * | 1971-06-25 | 1973-08-07 | Univ California | Pulmonary impedance bridge |
| US4291708A (en) * | 1977-11-02 | 1981-09-29 | Yeda Research & Development Co. Ltd. | Apparatus and method for detection of tumors in tissue |
| CN1114174A (en) * | 1994-05-23 | 1996-01-03 | 姚雪祥 | Automatic analyzing and diagnosing method and apparatus for hemotachogram |
| CN2577235Y (en) * | 2002-11-08 | 2003-10-01 | 中国科学院武汉岩土力学研究所 | High-precision gain-adjustable dynamic strain instrument |
| CN102662109A (en) * | 2012-04-16 | 2012-09-12 | 上海电机学院 | Balanced bridge |
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|---|---|---|---|---|
| US3750649A (en) * | 1971-06-25 | 1973-08-07 | Univ California | Pulmonary impedance bridge |
| US4291708A (en) * | 1977-11-02 | 1981-09-29 | Yeda Research & Development Co. Ltd. | Apparatus and method for detection of tumors in tissue |
| CN1114174A (en) * | 1994-05-23 | 1996-01-03 | 姚雪祥 | Automatic analyzing and diagnosing method and apparatus for hemotachogram |
| CN2577235Y (en) * | 2002-11-08 | 2003-10-01 | 中国科学院武汉岩土力学研究所 | High-precision gain-adjustable dynamic strain instrument |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106175773A (en) * | 2016-07-11 | 2016-12-07 | 芯海科技（深圳）股份有限公司 | Hand held multiband impedance breath signal measures system and measuring method |
| CN106175773B (en) * | 2016-07-11 | 2019-09-10 | 芯海科技（深圳）股份有限公司 | Hand held multiband impedance breath signal measuring system and measurement method |
| CN106805948A (en) * | 2017-03-10 | 2017-06-09 | 安徽通灵仿生科技有限公司 | A kind of children use finger cot type remote diagnosis system |
| CN106901706A (en) * | 2017-03-10 | 2017-06-30 | 安徽通灵仿生科技有限公司 | A kind of children gloves formula remote diagnosis system |
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|---|---|
| CN105380647B (en) | 2018-12-25 |
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