CN102854275B - Ion chromatography digital conductance detecting device based on digital signal processor (DSP) - Google Patents
Ion chromatography digital conductance detecting device based on digital signal processor (DSP) Download PDFInfo
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- CN102854275B CN102854275B CN201210264860.7A CN201210264860A CN102854275B CN 102854275 B CN102854275 B CN 102854275B CN 201210264860 A CN201210264860 A CN 201210264860A CN 102854275 B CN102854275 B CN 102854275B
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Abstract
The invention discloses an ion chromatography digital conductance detecting device based on a digital signal processor (DSP). The ion chromatography digital conductance detecting device comprises a digital conductance detector circuit board and a conductance detecting pond. Traditional thought of the ion chromatography digital conductance detecting device is abandoned from a measuring circuit and signal processing, digital programmable sine alternating current exciting signals are generated through the DSP and exerted on a conductance sensor, and electrode voltage and current are detected through I/V current detecting based on a microcurrent operational amplifier and a differential voltage detecting method with buffering input. By means of direct alternating current synchronous sampling, conductance signals are extracted out through a digital sine phase sensibility demodulation method through the DSP. In addition, real-time conductance rate of a solution can be output after temperature compensation. The ion chromatography digital conductance detecting device effectively improves flexibility and precision of ion chromatography conductance detecting, increases detecting range of the ion chromatography digital conductance detecting device, and reduces system noise and baseline drift.
Description
Technical field
The present invention relates to electrochemical measurement field, be specifically related to a kind of chromatography of ions numeral conductive detection device based on DSP.
Background technology
Ion chromatography electric conductivity detector is theoretical foundation based on Kohlraush law and Ohm law.As shown in Figure 3, as long as we are the voltage U of test detecting electrode and the electric current I that flows through detecting electrode in theory, can obtain the electricity of solution and lead G=I/U, yet affected by temperature, electric double layer capacitance, electrode polarization, conductor resistance, distributed capacitance etc., especially when low concentration sample is measured, these factor impacts are very large, actual conductance signal will be submerged in noise signal, can not accurately measure.Along with chromatography of ions application is more and more extensive, to the requirement of chromatography of ions sensitivity, sensing range, noise and drift, be also more and more higher, this traditional detection method of chromatography of ions and device have become the bottleneck of the development of chromatography of ions at present, invent a kind of new ion chromatograph conductance detection method and install extremely urgent.
Present stage, ion chromatography electric conductivity detector mainly adopted two electrodes and four electrode conductance ponds to detect, in circuit measuring method, mainly adopt the RC sine-wave oscillator of Wien bridge circuit or sine wave or the square wave of crystal oscillator composition to make pumping signal, be applied directly on electrode, it is mainly to adopt string electric resistance partial pressure method that electrode current detects, during inter-electrode voltage two electrode, directly from applying electrode, get voltage sample, the alternating voltage drawing, current signal connects diode rectifier circuit and changes into direct current signal after amplifying processing, again through Single-chip Controlling AD converter output conductance signal.This disposal route circuit is complicated, consuming time, and precision is not high, drift is large; And can only within the scope of ion intermediate concentration, use.Traditional treatment method has following five large shortcomings:
1) exciting signal frequency is fixed, and stablizes amplitude fluctuations large, and phase place lags behind;
2) resistance in series has been divided platen press surveyed current reduction detection sensitivity and measuring accuracy;
3) use the post processing circuitries such as rectification of complicated and time consumption, increased a large amount of analog devices, with non-linear hour sensitive analog device, use and can reduce measuring accuracy, increase the impact of temperature and the drift of baseline;
4) by obtaining lower noise with the low ∑-Δ type ADC of sample frequency, reduce greatly the time delay of system, affected the time at peak and the linearity of detection;
5) SCM Based control is not suitable for carrying out mass data computing, can not realize efficient filtering and digital signal processing algorithm, and this especially extracts the prerequisite ability of feeble signal at strong noise environment.
In Chinese Patent Application No., be in 201020207995.6, just to propose to adopt 24 for ADC light-coupled isolation
The method of sampling realizes optimizes chromatography of ions signals collecting, yet such as the resolution that improves ADC, increase the gain of amplifier, improve the methods such as excitation signal amplitude, limitation due to processing of circuit method itself, can not fundamentally solve raising sensitivity, increase sensing range, the problem such as noise decrease and drift, especially when low concentration ion detection, conductance cell sensor output signal changes faint, the amplitude of interchannel noise is close with actual conductance signal amplitude, these methods do not have any effect, can only rely on effective digital signal processing algorithm that useful signal is extracted from noise.
Summary of the invention
The present invention aims to provide the chromatography of ions numeral conductive detection device based on DSP of a kind of wide sensing range, high-precision sensitivity, peak time delay, the range of linearity are low for going out of solving from the method and apparatus of metering circuit that current chromatography of ions exists, noise and problem, the General Promotion chromatography of ions detector performance such as drift is large.
The technical solution used in the present invention is:
Chromatography of ions numeral conductive detection device based on DSP, it is characterized in that: include digital electric conductivity detector circuit board and conductance detecting pool, the circuit of described digital electric conductivity detector circuit board comprises digital signal processor DSP, digital-to-analog converter one, low-pass filter one, digital-to-analog converter two, low-pass filter two, input buffer circuit one, input buffer circuit two, electrode current detects and amplifying circuit, electrode voltage detects and amplifying circuit, low-pass filter three, low-pass filter four, ADC driving circuit 1, ADC driving circuit 2, high-speed ADC circuit, described digital signal processor DSP and digital-to-analog converter one, low-pass filter one forms excitation sine wave generator circuit, digital signal processor DSP and digital-to-analog converter two, low-pass filter two forms adjusts sine wave generator circuit, described conductance detecting pool includes a pond body, pond body is provided with two pipelines, two pipelines are connected to respectively solution container to be measured, waste fluid container, solution to be measured is housed in solution container to be measured, Chi Tizhong is also provided with conductivity sensor, temperature sensor, AD passage on the sheet of the signal output part incoming digital signal processor DSP of temperature sensor, conductivity sensor includes exciting electrode 1,4 and sampling electrode 2,3 and guarded electrode 5, described digital signal processor DSP, digital-to-analog converter one, low-pass filter one, input buffer circuit one connects successively, digital signal processor DSP and digital-to-analog converter one produce excitation sinusoidal signal, after filtering is processed, through input buffer circuit one, be applied on the exciting electrode 1 of conductivity sensor again, described digital signal processor DSP, digital-to-analog converter two, low-pass filter two, input buffer circuit two connects successively, the adjustment sinusoidal signal that digital signal processor DSP and digital-to-analog converter two produce, after filtering is processed, through input buffer circuit two, be applied on the pre-amplifier of electrode current detection and amplifying circuit again, pumping signal is from exciting electrode 1 input, after solution to be measured between electrode, from exciting electrode 4, export and be connected to the signal input part of electrode current detection and amplifying circuit, current detection circuit detects and flows through the current signal of conductivity sensor and carry out I/V conversion, voltage signal access low-pass filter three after conversion, filtered voltage signal outputs to high-speed ADC circuit by ADC driving circuit 1 circuit and carries out the sampled value that AD conversion draws electrode current signal, the sampling electrode 2,3 of conductivity sensor is connected respectively to the signal input part of electrode voltage detection and differential amplifier circuit, electrode voltage detection and differential amplifier circuit detect the voltage signal of 2,3, sampling electrode, and by this voltage signal access low-pass filter four, filtered voltage signal outputs to high-speed ADC circuit by ADC driving circuit 2 and carries out the sampled value that AD conversion draws electrode voltage signal, high-speed ADC circuit is connected with the buffered serial port MCBSPB of digital signal processor DSP by synchronous serial bus, the sampled value of the sampled value of electrode current signal and electrode voltage signal is transferred to digital signal processor DSP by MCBSPB, digital signal processor DSP, by the sampled value of electrode current, voltage signal being carried out to digital phase-locked computing, demodulates electrode voltage, current value by digital quadrature phase demodulation method, by aided algorithm and secondary digital filtering, draw actual useful electrode voltage U and electrode current I, obtain the electricity of effects of ion to be measured and lead.
Described digital signal processor DSP adopts TMS320F28335.
Described digital-to-analog converter one adopts DAC8801, and digital-to-analog converter two adopts ADS1174.
Described low-pass filter one, two, three all adopts five rank Butterworth LPF.
Advantage of the present invention is:
1, electricity is led and is detected excitation source signal and adopt DSP to control the sine wave able to programme that high-speed DAC produces, this sine wave amplitude, frequency, phase place of arranging able to programme, more current electricity lead detect in motivational techniques, have two large advanced:
A leads under unlike signal excitation and has different responses due to the electricity of solution, adopts single fixed frequency modes can not obtain high-resolution testing result, and programmable frequency regulates and makes us convenient for the preferentially frequency measurement of variable concentrations scope.
B, because sine wave is produced by DSP storage standards wave sequence, so it is phase-locked accurately to realize numeral, has eliminated the phase deviation that solution, lead capacitance and discharge circuit cause, improves input accuracy.
2, adopt high-speed ADC to carry out the AC synchronous sampling of current and voltage signals; Professional person all knows for solution conductivity and detects, and eliminate polarization of electrode effect, and the pumping signal pre processing circuit applying, certainly will introduce a large amount of non-linear simulation devices, thereby has increased noise and the drift of system.Yet adopt AC synchronous sampling method can improve the linearity and the sensitivity of detection, actual use can be reduced drift 2000uV for about 30 minutes.
3, the extracting method of signal we adopt digital quadrature phase demodulation method, for the high speed performance of DSP and superpower arithmetic capability, because standard signal is the output of storage DSP control store sequence, therefore can draw complete orthogonal signal, if restituted signal is U (n), i (n) and q (n) are standard orthogonal signal.N is the sampling number of ADC, and φ is initial phase.
------------------------------------------------?①
N gets even number can draw in-phase component R and quadrature component I according to trigonometric function orthogonal property:
Phase place:
; Amplitude:
The method that this method is used in detecting with current chromatography of ions is compared, and has simplified circuit, has overcome the problems such as analog device voltage drift, temperature drift and noise.And DSP directly controls the precise synchronization that has guaranteed reference signal and measured signal, demodulation accuracy is high, and especially with the obvious advantage in low concentration detects, noise robustness is better.
4, for the measurement of electric electrode current, adopt micro-electric current amplifier to carry out I/V conversion and realize current detecting, the sensitivity of this I-V transform DC micro-electric stream amplifier can reach 10
-15, the more current resistance in series sampling of this method, reduces impedance loop, has improved response sensitivity, has reduced noise and drift.
5, by conductivity sensor, provide special voltage sample electrode, use the differential electrical of band buffering input
Pressure detection method, not only effectively suppresses common mode interference, eliminates the error that electrode and lead impedance cause simultaneously.
Accompanying drawing explanation:
Fig. 1 is device schematic diagram of the present invention.
Fig. 2 is main circuit block scheme of the present invention.
Fig. 3 is that system of the present invention detects theory diagram.
Embodiment:
As Fig. 1, 2, shown in 3, chromatography of ions numeral conductive detection device based on DSP, include digital electric conductivity detector circuit board 1 and conductance detecting pool, the circuit of numeral electric conductivity detector circuit board 1 comprises digital signal processor DSP 8, digital-to-analog converter 9, low-pass filter 10, digital-to-analog converter 11, low-pass filter 12, input buffer circuit 13, input buffer circuit 14, electrode current detects and amplifying circuit 15, electrode voltage detects and amplifying circuit 16, low-pass filter 17, low-pass filter 20, ADC driving circuit 18, ADC driving circuit 21, high-speed ADC circuit 19, digital signal processor DSP 8 and digital-to-analog converter 9, low-pass filter 10 forms excitation sine wave generator circuit, digital signal processor DSP 8 and digital-to-analog converter 11, low-pass filter 12 forms adjusts sine wave generator circuit, conductance detecting pool includes a pond body 2, pond body 2 is provided with two pipelines 3, two pipelines 3 are connected to respectively solution container 4 to be measured, waste fluid container 5, in solution container 4 to be measured, solution to be measured is housed, Chi Tizhong is also provided with conductivity sensor 6, temperature sensor 7, AD passage on the sheet of the signal output part incoming digital signal processor DSP8 of temperature sensor 7, conductivity sensor 5 includes exciting electrode 1,4 and sampling electrode 2,3 and guarded electrode 5, digital signal processor DSP 8, digital-to-analog converter 9, low-pass filter 10, input buffer circuit 13 connects successively, digital signal processor DSP 8 produces excitation sinusoidal signal with digital-to-analog converter 9, after filtering is processed, through input buffer circuit 13, be applied on the exciting electrode 1 of conductivity sensor 6 again, digital signal processor DSP 8, digital-to-analog converter 11, low-pass filter 12, input buffer circuit 14 connects successively, the adjustment sinusoidal signal that digital signal processor DSP 8 and digital-to-analog converter 11 produce, after filtering is processed, through input buffer circuit 14, be applied on the pre-amplifier of electrode current detection and amplifying circuit 15 again, pumping signal is from exciting electrode 1 input, after solution to be measured between electrode, from exciting electrode 4, export and be connected to the signal input part of electrode current detection and amplifying circuit 15, current detection circuit detects and flows through the current signal of conductivity sensor 6 and carry out I/V conversion, voltage signal access low-pass filter 17 after conversion, filtered voltage signal outputs to high-speed ADC circuit 19 by ADC driving circuit 18 circuit and carries out the sampled value that AD conversion draws electrode current signal, the sampling electrode 2,3 of conductivity sensor 6 is connected respectively to the signal input part of electrode voltage detection and differential amplifier circuit 16, electrode voltage detection and differential amplifier circuit 16 detect the voltage signal of 2,3, sampling electrode, and by this voltage signal access low-pass filter 20, filtered voltage signal outputs to high-speed ADC circuit 19 by ADC driving circuit 21 and carries out the sampled value that AD conversion draws electrode voltage signal, high-speed ADC circuit 19 is connected with the buffered serial port MCBSPB of digital signal processor DSP 8 by synchronous serial bus, the sampled value of the sampled value of electrode current signal and electrode voltage signal is transferred to digital signal processor DSP 8 by MCBSPB, digital signal processor DSP 8, by the sampled value of electrode current, voltage signal being carried out to digital phase-locked computing, demodulates electrode voltage, current value by digital quadrature phase demodulation method, by aided algorithm and secondary digital filtering, draw actual useful electrode voltage U and electrode current I, obtain the electricity of effects of ion to be measured and lead.
Digital signal processor DSP 8 adopts TMS320F28335.
Digital-to-analog converter 9 adopts DAC8801, and digital-to-analog converter 11 adopts ADS1174.
Low-pass filter 10,12,17 all adopts five rank Butterworth LPF.
By high precision floating-point signal processor F28335, be system master CPU, F28335 clock can reach 150MHz, and two road multichannel buffered serial ports can directly configure DMA pattern.In conductivity sensor, preset temperature sensor is sent to temperature signal AD passage AD0 and AD1 on the sheet of F28335, draws Current Temperatures t, obtains the temperature compensation value к 0 of conductivity by built-in temperature compensation meter; According to the constant K of measuring the conductivity sensor of demarcating, obtain real solution conductivity к=K*G+ к 0, conductivity data compressed encoding is sent to host computer workstation and instrument display screen by RS232 telecommunication circuit, communication baud rate is set to 115200.
Claims (4)
1. the numeral of the chromatography of ions based on a DSP conductive detection device, includes digital electric conductivity detector circuit board and conductance detecting pool, and conductance detecting pool includes a pond body, and pond body is provided with two pipelines, and two pipelines are connected to respectively solution container to be measured, waste fluid container, is equipped with solution to be measured in solution container to be measured, Chi Tizhong is also provided with conductivity sensor, temperature sensor, the AD passage on the sheet of the signal output part incoming digital signal processor DSP of temperature sensor, conductivity sensor includes exciting electrode 1, 4 and sampling electrode 2, 3 and guarded electrode 5, it is characterized in that: the circuit of described digital electric conductivity detector circuit board comprises digital signal processor DSP, digital-to-analog converter one, low-pass filter one, digital-to-analog converter two, low-pass filter two, input buffer circuit one, input buffer circuit two, electrode current detects and amplifying circuit, electrode voltage detects and amplifying circuit, low-pass filter three, low-pass filter four, ADC driving circuit 1, ADC driving circuit 2, high-speed ADC circuit, described digital signal processor DSP and digital-to-analog converter one, low-pass filter one forms excitation sine wave generator circuit, digital signal processor DSP and digital-to-analog converter two, low-pass filter two forms adjusts sine wave generator circuit, described digital signal processor DSP, digital-to-analog converter one, low-pass filter one, input buffer circuit one connects successively, digital signal processor DSP and digital-to-analog converter one produce excitation sinusoidal signal, after filtering is processed, through input buffer circuit one, be applied on the exciting electrode 1 of conductivity sensor again, described digital signal processor DSP, digital-to-analog converter two, low-pass filter two, input buffer circuit two connects successively, the adjustment sinusoidal signal that digital signal processor DSP and digital-to-analog converter two produce, after filtering is processed, through input buffer circuit two, be applied on the pre-amplifier of electrode current detection and amplifying circuit again, pumping signal is from exciting electrode 1 input, after solution to be measured between electrode, from exciting electrode 4, export and be connected to the signal input part of electrode current detection and amplifying circuit, electrode current detects with amplifying circuit and detects and flow through the current signal of conductivity sensor and carry out I/V conversion, voltage signal access low-pass filter three after conversion, filtered voltage signal outputs to high-speed ADC circuit by ADC driving circuit 1 circuit and carries out the sampled value that AD conversion draws electrode current signal, the sampling electrode 2,3 of conductivity sensor is connected respectively to the signal input part of electrode voltage detection and differential amplifier circuit, electrode voltage detection and differential amplifier circuit detect the voltage signal of 2,3, sampling electrode, and by this voltage signal access low-pass filter four, filtered voltage signal outputs to high-speed ADC circuit by ADC driving circuit 2 and carries out the sampled value that AD conversion draws electrode voltage signal, high-speed ADC circuit is connected with the buffered serial port MCBSPB of digital signal processor DSP by synchronous serial bus, the sampled value of the sampled value of electrode current signal and electrode voltage signal is transferred to digital signal processor DSP by MCBSPB, digital signal processor DSP, by the sampled value of electrode current, voltage signal being carried out to digital phase-locked computing, demodulates electrode voltage, current value by digital quadrature phase demodulation method, by aided algorithm and secondary digital filtering, draw actual useful electrode voltage U and electrode current I, obtain the electricity of effects of ion to be measured and lead.
2. the chromatography of ions numeral conductive detection device based on DSP according to claim 1, is characterized in that: described digital signal processor DSP adopts TMS320F28335.
3. the chromatography of ions numeral conductive detection device based on DSP according to claim 1, is characterized in that: described digital-to-analog converter one adopts DAC8801, and digital-to-analog converter two adopts ADS1174.
4. the chromatography of ions numeral conductive detection device based on DSP according to claim 1, is characterized in that: described low-pass filter one, two, three all adopts five rank Butterworth LPF.
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| CN108279625B (en) * | 2017-12-30 | 2023-09-05 | 利穗科技(苏州)有限公司 | Digital chromatography system and method |
| CN110646678A (en) * | 2019-10-10 | 2020-01-03 | 杭州绿洁环境科技股份有限公司 | Conductivity measuring device |
| CN112763547B (en) * | 2020-12-30 | 2022-10-25 | 安徽皖仪科技股份有限公司 | Conductivity detection system based on dipolar conductivity cell |
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