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CN-224216781-U - PH electrode internal resistance measuring circuit

CN224216781UCN 224216781 UCN224216781 UCN 224216781UCN-224216781-U

Abstract

The utility model discloses a pH electrode internal resistance measuring circuit which comprises an excitation source circuit, a first measuring circuit, a second measuring circuit and a current measuring circuit. According to the pH electrode internal resistance measuring circuit, the simulation switch is used for applying the excitation source to the pH electrode, and meanwhile, the change of voltage and current is measured, so that the pH electrode internal resistance can be conveniently and rapidly detected, the circuit scheme is simple, the cost is low, and the measurement is accurate. The excitation source is applied without a transformer, and only an operational amplifier and an analog switch are used, so that the circuit miniaturization is facilitated.

Inventors

  • SUN SHUAI

Assignees

  • 上海忻成科技有限公司

Dates

Publication Date
20260508
Application Date
20250514

Claims (9)

  1. 1. The pH electrode internal resistance measuring circuit is characterized by comprising an excitation source circuit, a first measuring circuit, a second measuring circuit and a current measuring circuit; The excitation source circuit is connected with the first end of the pH electrode and is used for applying a controllable excitation source when the internal resistance of the pH electrode is measured; The first measuring circuit is connected with the first end of the pH electrode and is used for measuring the voltage of the pH+ end; the second measuring circuit is connected with the second end of the pH electrode and is used for measuring the voltage of the pH-end; The current measuring circuit is connected with the second end of the pH electrode and is used for measuring the current flowing through the pH electrode; The first end of the pH electrode is a glass electrode, the second end of the pH electrode is a reference electrode, or the first end of the pH electrode is a reference electrode, and the second end of the pH electrode is a glass electrode.
  2. 2. The pH electrode internal resistance measurement circuit according to claim 1, wherein: The excitation source circuit comprises a first digital-to-analog converter DAC, a first fifth operational amplifier U15, a first fourth analog switch U14, a first fifth resistor R15, a first sixth resistor R16, a first seventh resistor R17 and a third resistor R33; The non-inverting input end of the first fifth operational amplifier U15 is connected with the first digital-to-analog converter DAC through a third resistor R33, the inverting input end of the first fifth operational amplifier U15 is respectively connected with the second end of the first fifth resistor R15 and the first end of a first sixth resistor R16, and the second end of the first sixth resistor R16 is grounded; The first end of the first fifth resistor R15 is respectively connected with the second end of the first seventh resistor R17 and the output end of the first fifth operational amplifier U15, the first end of the first seventh resistor R17 is connected with the second end of the first fourth analog switch U14, and the first end of the first fourth analog switch U14 is connected with the positive electrode of the pH electrode.
  3. 3. The pH electrode internal resistance measurement circuit according to claim 2, wherein: the first digital-to-analog converter DAC is used for outputting set voltage, the first five operational amplifier U15 amplifies the set voltage output by the first digital-to-analog converter DAC in phase, and the first four analog switches U14 control the on-off of the excitation source and the pH electrode.
  4. 4. The pH electrode internal resistance measurement circuit according to claim 1, wherein: The first measurement circuit comprises a first sixth operational amplifier U16, a first seventh operational amplifier U17, a second digital-to-analog converter ADC2, a third fourth resistor R34, a third fifth resistor R35, a third sixth resistor R36, a seventh resistor R37 and a second eighth capacitor C28; The positive input end of the first sixth operational amplifier U16 is connected with the positive electrode of the pH electrode, the negative input end of the first sixth operational amplifier U16 is respectively connected with the output end of the first sixth operational amplifier U16 and the first end of the third fourth resistor R34, and the second end of the third fourth resistor R34 is connected with the positive input end of the first seventh operational amplifier U17; The inverting input end of the first seventh operational amplifier U17 is respectively connected with the second end of the third sixth resistor R36 and the first end of the seventh resistor R37, the first end of the third sixth resistor R36 is grounded, the second end of the seventh resistor R37 is respectively connected with the output end of the first seventh operational amplifier U17 and the first end of the third fifth resistor R35, the second end of the third fifth resistor R35 is respectively connected with the first end of the second eighth capacitor C28 and the second digital-to-analog converter ADC2, and the second end of the second eighth capacitor C28 is grounded.
  5. 5. The pH electrode internal resistance measurement circuit according to claim 4, wherein: The first sixth operational amplifier U16 is a high internal resistance operational amplifier, forms a voltage follower, buffers the voltage at the pH+ end, and the first seventh operational amplifier U17 amplifies the voltage in phase, so that the voltage is more easily and accurately collected by the second digital-to-analog converter ADC 2.
  6. 6. The pH electrode internal resistance measurement circuit according to claim 1, wherein: The second measurement circuit comprises a first eighth operational amplifier U18, a second sixth operational amplifier U26, a third digital-to-analog converter ADC3, a third eighth resistor R38, a third ninth resistor R39, a fourth zero resistor R40, a fourth first resistor R41 and a third zero capacitor C30; The positive input end of the first eighth operational amplifier U18 is connected with the negative electrode of the pH electrode, the negative input end of the first eighth operational amplifier U18 is respectively connected with the output end of the first eighth operational amplifier U18 and the first end of the third eighth resistor R38, and the second end of the third eighth resistor R38 is connected with the positive input end of the second sixth operational amplifier U26; the inverting input end of the second sixth operational amplifier U26 is respectively connected with the second end of the fourth zero resistor R40 and the first end of the fourth first resistor R41, the first end of the fourth zero resistor R40 is grounded, and the second end of the fourth first resistor R41 is respectively connected with the output end of the second sixth operational amplifier U26 and the first end of the third ninth resistor R39; The second end of the third nine resistor R39 is respectively connected with the first end of the third zero capacitor C30 and the third digital-to-analog converter ADC3, and the second end of the third zero capacitor C30 is grounded.
  7. 7. The pH electrode internal resistance measurement circuit according to claim 6, wherein: the first eighth operational amplifier U18 is a high internal resistance operational amplifier, the first eighth operational amplifier U18 forms a voltage follower to buffer the voltage of the pH-end, and the operational amplifier U26 amplifies the voltage in phase, so that the voltage is more easily and accurately collected by the third digital-to-analog converter ADC 3.
  8. 8. The pH electrode internal resistance measurement circuit according to claim 1, wherein: The current measurement circuit comprises a second seventh operational amplifier U27, a second eighth operational amplifier U28, a fourth digital-to-analog converter ADC4, a fourth second resistor R42, a fourth third resistor R43, a fourth resistor R44, a fourth fifth resistor R45, a fourth seventh resistor R47, a third first capacitor C31 and a fourth capacitor C44; the positive-phase input end of the second seventh operational amplifier U27 is grounded, and the negative electrode of the pH electrode, the first end of the fourth seventh resistor R47 and the first end of the fourth capacitor C44 are respectively connected with the negative input end of the second seventh operational amplifier U27, the second end of the fourth seventh resistor R47, the second end of the fourth capacitor C44 and the first end of the fourth second resistor R42; The second end of the fourth resistor R42 is connected with the positive input end of the second eighth operational amplifier U28, the negative input end of the second eighth operational amplifier U28 is respectively connected with the second end of the fourth resistor R44 and the first end of the fourth fifth resistor R45, the first end of the fourth resistor R44 is grounded, the output end of the second eighth operational amplifier U28 is respectively connected with the second end of the fourth fifth resistor R45 and the first end of the fourth third resistor R43, the second end of the fourth third resistor R43 is respectively connected with the first end of the third capacitor C31 and the fourth digital-to-analog converter ADC4, and the second end of the third capacitor C31 is grounded.
  9. 9. The pH electrode internal resistance measurement circuit according to claim 8, wherein: The second seventh operational amplifier U27 is a precision operational amplifier, the second seventh operational amplifier U27, the resistor R47 and the capacitor C64 form a transimpedance amplifier, the current on the pH electrode is converted into a voltage, and the second eighth operational amplifier U28 amplifies the voltage in phase, so that the voltage is more easily and accurately collected by the fourth digital-analog converter ADC 4.

Description

PH electrode internal resistance measuring circuit Technical Field The utility model belongs to the technical field of pH electrode detection, and relates to a measuring circuit, in particular to a pH electrode internal resistance measuring circuit. Background The pH electrode is also called a pH probe and a pH sensor, and the English name pHelectrode or pHsensor is a device for representing the pH value by measuring the electrode potential at the part of the pH meter which is contacted with the measured substance. The pH electrode is constantly worn during use and needs to be replaced periodically. Most of the acquisition circuits and transmitters of pH electrodes in the market at present do not have the function of detecting the pH state, so that early warning cannot be performed in advance, maintenance personnel can only maintain the pH electrode until the pH measured value is abnormal, and the pH electrode is very inconvenient in field application. In view of this, there is a strong need to design a new pH electrode detection method to overcome at least some of the above-mentioned drawbacks of the existing pH electrode usage methods. Disclosure of utility model The utility model provides a pH electrode internal resistance measuring circuit which can conveniently and rapidly detect the pH electrode internal resistance, and has the advantages of simple circuit scheme, low cost and accurate measurement. In order to solve the technical problems, according to one aspect of the present utility model, the following technical scheme is adopted: the pH electrode internal resistance measuring circuit comprises an excitation source circuit, a first measuring circuit, a second measuring circuit and a current measuring circuit; The excitation source circuit is connected with the first end of the pH electrode and is used for applying a controllable excitation source when the internal resistance of the pH electrode is measured; The first measuring circuit is connected with the first end of the pH electrode and is used for measuring the voltage of the pH+ end; the second measuring circuit is connected with the second end of the pH electrode and is used for measuring the voltage of the pH-end; The current measuring circuit is connected with the second end of the pH electrode and is used for measuring the current flowing through the pH electrode; The first end of the pH electrode is a glass electrode, the second end of the pH electrode is a reference electrode, or the first end of the pH electrode is a reference electrode, and the second end of the pH electrode is a glass electrode. As one embodiment of the present utility model, the excitation source circuit includes a first digital-to-analog converter DAC, a first fifth operational amplifier U15, a first fourth analog switch U14, a first fifth resistor R15, a first sixth resistor R16, a first seventh resistor R17, and a third resistor R33; The non-inverting input end of the first fifth operational amplifier U15 is connected with the first digital-to-analog converter DAC through a third resistor R33, the inverting input end of the first fifth operational amplifier U15 is respectively connected with the second end of the first fifth resistor R15 and the first end of a first sixth resistor R16, and the second end of the first sixth resistor R16 is grounded; The first end of the first fifth resistor R15 is respectively connected with the second end of the first seventh resistor R17 and the output end of the first fifth operational amplifier U15, the first end of the first seventh resistor R17 is connected with the second end of the first fourth analog switch U14, and the first end of the first fourth analog switch U14 is connected with the positive electrode of the pH electrode. As an embodiment of the present utility model, the first DAC is configured to output a set voltage, the first fifth op-amp U15 amplifies the set voltage output by the first DAC in phase, and the first fourth analog switch U14 controls on/off of the excitation source and the pH electrode. As an embodiment of the present utility model, the first measurement circuit includes a first sixth operational amplifier U16, a first seventh operational amplifier U17, a second digital-to-analog converter ADC2, a third fourth resistor R34, a third fifth resistor R35, a third sixth resistor R36, a seventh resistor R37, and a second eighth capacitor C28; The positive input end of the first sixth operational amplifier U16 is connected with the positive electrode of the pH electrode, the negative input end of the first sixth operational amplifier U16 is respectively connected with the output end of the first sixth operational amplifier U16 and the first end of the third fourth resistor R34, and the second end of the third fourth resistor R34 is connected with the positive input end of the first seventh operational amplifier U17; The inverting input end of the first seventh operational amplifier U17 is respectively co