CN203502500U

CN203502500U - Solution conductivity measuring circuit

Info

Publication number: CN203502500U
Application number: CN201320670020.0U
Authority: CN
Inventors: 高玉琴
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-10-29
Filing date: 2013-10-29
Publication date: 2014-03-26
Anticipated expiration: 2023-10-29

Abstract

The utility model relates to a solution conductivity measuring circuit; a 555 time-base integrated circuit IC, a resistor R1 and a resistor R2, a capacitor C and a capacitor C1 and a conductivity electrode DDJ form a square wave oscillator; an electronic switch controls a charge-discharge loop of the capacitor C, so the current passing the conductivity electrode is AC current; the frequency of a measuring circuit output signal and a solution resistance in the conductivity electrode are in a corresponding relation; the measuring circuit is simple in structure, can automatically compensate errors generated in capacitance effect and polarization of the conductivity electrode in the measuring process, and has high measuring precision.

Description

A kind of metering circuit of electrical conductivity of solution

Technical field

The utility model relates to a kind of metering circuit of electrical conductivity of solution.

Background technology

To the measuring method of electrical conductivity of solution, be for a long time, a conductance electrode is inserted in solution, the electric conductivity of solution can be used the solution resistance R in conductance electrode _x inverse electricity lead 1/R _xrepresent, by solution resistance R _xafter connecting with a reference resistance R, at the two ends of this series circuit, apply on the interface that an alternating voltage U(alternating voltage can not make electrode contact with solution and polarize, guarantee the accuracy of measuring), then measure the voltage U on solution resistance _x, according to Ohm law U _x=U * R _x/ (R _x+ R) known, voltage U _xwith solution resistance R _xbecome a corresponding relation.Yet the structure of the measurement mechanism that this measuring method is used is comparatively complicated: 1, an oscillator device need to be set and produce alternating voltage U, an amplifying circuit also will be set to measured signal voltage U _xamplify, to the signal voltage U after amplifying _xalso need to carry out rectification and convert thereof into direct-flow signal voltage; 2, oscillator being had to higher requirement is that the amplitude of the output signal voltage of oscillator must guarantee to stablize.Moreover need to automatically control the conductivity of solution in many occasions, this need to convert the direct current simulation signal of conductivity to digital signal, for computer control system, process, converting direct current simulation signal to digital signal also needs an A/D conversion equipment.

Utility model content

The technical problems to be solved in the utility model is to provide a kind of metering circuit of electrical conductivity of solution, and this metering circuit simple in structure can directly be exported the frequency signal corresponding with electrical conductivity of solution.

Metering circuit of the present utility model comprises, time-base integrated circuit IC, resistance R 1-R2, capacitor C, C1; The pin 5 of time-base integrated circuit IC is by capacitor C 1 ground connection, and the pin 8 of time-base integrated circuit IC, pin 1 are connected with ground with power vd D respectively, and the pin 4 of time-base integrated circuit IC meets power vd D; The pin 2 of time-base integrated circuit IC, pin 6 are connected with one end of capacitor C, the other end ground connection of capacitor C, and one end of resistance R 1, R2 is connected, the pin 7 of another termination time-base integrated circuit of resistance R 2; It is characterized in that, described metering circuit also comprises resistance R 3, R4, triode T1, T2, conductance electrode DDJ, the collector of triode T1 is connected with the other end of resistance R 1, the emitter of triode T1 meets power vd D, the base stage of triode T1 connects the collector of triode T2 by resistance R 3, the grounded emitter of triode T2, the base stage of triode T2 is connected with the pin 3 of time-base integrated circuit by resistance R 4, and described conductance electrode DDJ two ends are connected with one end of resistance R 2 and the pin 2 of time-base integrated circuit IC respectively; Conductance electrode DDJ is solution resistance signal input part, and the pin 3 of time-base integrated circuit is measuring-signal output terminal.

Be characterized in, 1, utilize 555 time-base integrated circuits and conductance electrode to form a square-wave oscillator, the signal frequency of the solution resistance of conductance electrode and oscillator output is a corresponding relation, and circuit structure is simple; 2, the frequency that flows through the alternating current of solution resistance can change automatically with the size of solution resistance, effectively reduces the measuring error that electricity conduction shunt capacitance effect and polarization bring.

Accompanying drawing explanation

Fig. 1 is electrical schematic diagram of the present utility model.

Fig. 2 is the oscillogram of reference point in Fig. 1.

Fig. 3 is the equivalent function circuit diagram of time-base integrated circuit.

Embodiment

Existing accompanying drawings embodiment of the present utility model.

As shown in Figure 1, it comprises time-base integrated circuit IC to metering circuit of the present utility model, resistance R 1-R2, capacitor C, C1; The pin 5 of time-base integrated circuit IC carries out filtering by capacitor C 1 ground connection to the dry signal of scratching, the pin 8 of time-base integrated circuit IC, pin 1 are that working power input end is connected with ground with power vd D respectively, and the pin 4 of time-base integrated circuit IC meets power vd D makes the triode BG2 in time-base integrated circuit remain on cut-off state; The pin 2 of time-base integrated circuit IC, pin 6 are connected with one end of capacitor C, the other end ground connection of capacitor C, and one end of resistance R 1, R2 is connected, the pin 7 of another termination time-base integrated circuit of resistance R 2; It is characterized in that, described metering circuit also comprises resistance R 3, R4, triode T1, T2, conductance electrode DDJ, the collector of triode T1 is connected with the other end of resistance R 1, the emitter of triode T1 meets power vd D, the base stage of triode T1 connects the collector of triode T2 by resistance R 3, the grounded emitter of triode T2, the base stage of triode T2 is connected with the pin 3 of time-base integrated circuit by resistance R 4, and described conductance electrode DDJ two ends are connected with one end of resistance R 2 and the pin 2 of time-base integrated circuit IC respectively; Conductance electrode DDJ is solution resistance signal input part, and the pin 3 of time-base integrated circuit is measuring-signal output terminal.

Described resistance R 3, R4, triode T1, T2 form an electronic switch, triode T1 conducting when the pin 3 of time-base integrated circuit is high level, triode T1 cut-off when pin 3 is low level.

The signal of described triode T1 is 9012, and the signal of triode T2 is 9013.

The model of described time-base integrated circuit is a kind of in NE555 or 555 series, and its equivalent function as shown in Figure 3.

Fig. 1 circuit forms a square-wave oscillator, the solution resistance Rx of conductance electrode can be converted to corresponding frequency signal output.Its principle of work is:

Conductance electrode inserts in solution, between the pole piece of conductance electrode, there is a solution resistance Rx, after adding power vd D, because the voltage in capacitor C can not suddenly change, output terminal (pin 3) output signal Vo is high level " 1 ", and triode BG1 in time-base integrated circuit cut-off, triode T1 conducting, capacitor C is by resistance R 1, the solution resistance Rx of conductance electrode charges to it, pin 2 current potentials are index rising with the rising of the terminal voltage in capacitor C, as 0-t1 section capacitance voltage uc waveform in Fig. 2, output signal Vo waveform, triode BG1 state waveform (oblique line filling part is conducting region), shown in triode T1 state waveform (oblique line filling part is conducting region).

Voltage in capacitor C increases in time, when the level on pin 6 reaches 2/3 supply voltage value, upper comparer A1 upset, make rest-set flip-flop (being formed by Sheffer stroke gate F1, F2) set, through phase inverter F3 paraphase, the output signal Vo of the output terminal of time-base integrated circuit (pin 3) is low level " 0 ".Now triode BG1 conducting, triode T1 cut-off, electric charge in capacitor C flows to triode BG1(pin 7 through solution resistance Rx, resistance R 2) electric discharge, voltage in capacitor C declines in time, when the level on pin 2 drops to 1/3 supply voltage, comparer A2 upset, rest-set flip-flop resets, after paraphase, make output terminal (pin 3) be high level " 1 ".As shown in t1-t2 section capacitance voltage uc waveform, output signal Vo waveform, triode BG1 state waveform, triode T1 state waveform in Fig. 2.

Above process repeats as shown in t3-t5 section waveform in Fig. 2, forms vibration, and when vibration, the duration of charging of capacitor C is

Tc = 0.693（R1 + Rx ）C （1）

Be the discharge time of capacitor C

Tf = 0.693（R2+ Rx）C （2）

Be oscillation period

T = Tc + Tf

= 0.693（R1+R2 + 2Rx ）C （3）

Oscillation frequency is

f = 1/T = 1.443 /（R1+R2 + 2Rx ）C （4）

From formula 4, resistance R 1, R2, capacitor C are all constants, and the variation of oscillation frequency is only relevant with the variation of solution resistance, and oscillation frequency and solution resistance have a corresponding relation.

Charge and discharge along with capacitor C, on solution resistance, can form an alternating current, the resistance of power taking resistance R1, R2 equates, can make the positive half cycle of electric current that flows through solution resistance equate with negative half period, flow through the electric current of solution resistance not containing DC component, as shown in electric current I waveform in Fig. 2, reduce polarization of electrode phenomenon.

Another feature of the utility model is can flow through with the big or small auto-changing of electrical conductivity of solution the power frequency of solution resistance, shunt capacitance effect errors and the polarisation error of auto-compensation conductance cell.Compensation principle is described as follows:

Described shunt capacitance is because of the mutual migration of electric charge and the electric charge formed electric capacity of migration for electrode, and two pole pieces of it and conductance electrode are in parallel, and its capacity is about tens picofarads.(as distilled water, pure water) its resistance large (being greater than 100K ohm) when electrolysis of solutions matter concentration is lower, impact due to shunt capacitance, can make measured conductivity be greater than standard value, for reducing the impact of shunt capacitance, conventionally adopt lower power frequency (lower than 100HZ);

Its resistance less (being less than 100 ohm) when the electrolyte concentration of solution is higher, current density on conductance electrode is crossed conference and is caused polarization, show as at electrode surface and form electrostatic double layer or near the concentration of electrolytic solution conductance electrode is changed, this just makes equivalent solution resistance increase, and produces measuring error.According to electrochemical theory, can release the Wu Cha ⊿ R causing due to polarization,

⊿R＝E ²/fRx ² (5)

In formula 5, E is that polarization potential is relevant with the alternating-current voltage source being applied on solution resistance, and f is ac power frequency, and Rx is interelectrode solution resistance;

From formula 5, can find out and adopt high ac power frequency can reduce polarisation error.

The utility model can be with the size of solution resistance when measuring conductivity automatic change frequency, from formula 4, can find out, the power frequency hour flowing through wherein when solution resistance is higher, the power frequency flowing through when solution resistance is larger is wherein higher.The capacity 0.1uf of capacitor C, the resistance of resistance R 1, R2 is got 100 ohm, and the variation range of the solution resistance Rx between conductance electrode is at 50 ohm-100K ohm, and the frequency range of the conductivity signal of output is 7000HZ-70HZ, and measuring error can be less than 2%.Therefore shunt capacitance effect errors and polarisation error that can auto-compensation conductance cell.

The power supply vdd voltage of this metering circuit is+6V, and during use, its output terminal pin 3 can directly be connected with the input port of a single-chip microcomputer, and single-chip microcomputer plug-in calculates the frequency signal receiving, and converts frequency values to conductivity value, for showing, controlling.

Claims

1. a metering circuit for electrical conductivity of solution, it comprises time-base integrated circuit IC, resistance R 1-R2, capacitor C, C1; The pin 5 of time-base integrated circuit IC is by capacitor C 1 ground connection, and the pin 8 of time-base integrated circuit IC, pin 1 are connected with ground with power vd D respectively, and the pin 4 of time-base integrated circuit IC meets power vd D; The pin 2 of time-base integrated circuit IC, pin 6 are connected with one end of capacitor C, the other end ground connection of capacitor C, and one end of resistance R 1, R2 is connected, the pin 7 of another termination time-base integrated circuit of resistance R 2; It is characterized in that, described metering circuit also comprises resistance R 3, R4, triode T1, T2, conductance electrode DDJ, the collector of triode T1 is connected with the other end of resistance R 1, the emitter of triode T1 meets power vd D, the base stage of triode T1 connects the collector of triode T2 by resistance R 3, the grounded emitter of triode T2, the base stage of triode T2 is connected with the pin 3 of time-base integrated circuit by resistance R 4, and described conductance electrode DDJ two ends are connected with one end of resistance R 2 and the pin 2 of time-base integrated circuit IC respectively; Conductance electrode DDJ is solution resistance signal input part, and the pin 3 of time-base integrated circuit is measuring-signal output terminal.

2. the metering circuit of electrical conductivity of solution according to claim 1, is characterized in that, the capacity of described capacitor C is 0.1uf, and the resistance of resistance R 1, R2 is 100 ohm, and the variation range of the solution resistance between conductance electrode is 50 ohm-100K ohm.