A high-interference-resistant and long-distance pH measurement system

Abstract

The present invention discloses a novel, highly interference-resistant, long-distance pH measurement system, comprising: a composite pH electrode bulb; a first lead connected to the composite pH electrode bulb and an Ag / AgCl reference electrode; a second lead connected to the Ag / AgCl reference electrode; a shielding layer sleeved around the outside of the second lead; and the second reference electrode, the lead of the second reference electrode being connected to an outer shielding layer; a common-mode rejection shielding drive circuit, an impedance conversion circuit, and a modulation and demodulation circuit; the first and second leads being connected to the common-mode rejection shielding drive circuit and the impedance conversion circuit, and the outer shielding layer being connected to the modulation and demodulation circuit. According to the present invention, the lead length of a conventional glass bulb electrode is significantly reduced through special shielding technology and a back-end acquisition circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of pH measurement, and in particular to a high-interference-resistant and long-distance pH measurement system. Background Art

[0002] In recent years, with the continuous advancement of water quality testing technology, higher requirements have been placed on pH electrode detection and transmission. Conventional pH electrodes currently on the market use glass bulbs with extremely high internal resistance. Consequently, even with coaxial cables, the leads are too long, resulting in poor interference resistance. Long-distance measurements generally utilize digital electrodes with 485 communication. However, the digital electrode's circuit board occupies internal space within the pH electrode, reducing the internal reference solution volume and ultimately significantly shortening the electrode's lifespan. Summary of the Invention

[0003] To address the shortcomings of the prior art, the present invention provides a highly interference-resistant, long-distance pH measurement system. By utilizing special shielding technology and a back-end acquisition circuit, the lead length of a conventional glass bulb electrode is significantly reduced. To achieve these and other advantages, the present invention provides a highly interference-resistant, long-distance pH measurement system comprising:

[0004] A composite pH electrode bulb, a first lead connected to the composite pH electrode bulb and an Ag / AgCl reference electrode, a second lead connected to the Ag / AgCl reference electrode, a shielding layer sleeved on the outside of the second lead, and a second reference electrode, wherein the lead of the second reference electrode is connected to an outer shielding layer;

[0005] Common mode rejection shielding driving circuit, impedance conversion circuit and modulation and demodulation circuit;

[0006] The first lead and the second lead are connected to the common mode suppression shielding driving circuit and the impedance conversion circuit, and the outer shielding layer is connected to the modulation and demodulation circuit.

[0007] Preferably, the first lead is connected to a first high-impedance input operational amplifier, the first high-impedance input operational amplifier is connected in series with a third resistor, the third resistor is connected in series with a sixth resistor, and the sixth resistor is connected in parallel with the first capacitor and the differential amplifier.

[0008] Preferably, a first resistor is connected in parallel between the first high-impedance input operational amplifier and the third resistor, a second resistor is connected in series with the first resistor, a shielding driver is connected in parallel between the first resistor and the second resistor, and an output end of the shielding driver is connected to the shielding layer.

[0009] Preferably, the second resistor is connected in parallel with a fourth resistor, the fourth resistor is connected in series with a second high-impedance input operational amplifier, the non-inverting input terminal of the second high-impedance input operational amplifier is connected to a second lead, the fourth resistor is connected in series with a fifth resistor, and the fifth resistor is connected to the ground wire.

[0010] Preferably, a differential amplifier is connected in parallel between the fourth resistor and the fifth resistor, a demodulator is connected in series to the differential amplifier, and an output end of the demodulator can be connected to a voltage acquisition circuit.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] (1) The optical fiber core of the high-anti-interference long-distance pH measurement system of the present invention adopts a flexible transparent core and a dyed core, which breaks through the material limitation of the glass fiber of the traditional optical fiber core, is tensile-resistant and flexural-resistant, and can also realize the measurement of bending angle and position.

[0013] (2) The absorbent color dye applied to the cavity of the dye core of the present invention is not only economical and practical, but also has a simple and easy-to-understand working principle and a good working effect.

[0014] (3) All components of the high-anti-interference long-distance pH measurement system of the present invention have low production costs and simple structures, and can achieve functions similar to those of traditional optical fiber sensors. Under certain conditions, they can measure physical parameters such as strain, temperature and pressure with high precision and over long distances. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A partial circuit diagram of a high-anti-interference long-distance pH measurement system according to the present invention;

[0016] Figure 2 Schematic diagram of the equivalent circuit of the pH electrode leads of the high-anti-interference long-distance pH measurement system according to the present invention;

[0017] Figure 3 Schematic diagram of the overall appearance of the high-anti-interference long-distance pH measurement system according to the present invention. DETAILED DESCRIPTION

[0018] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0019] Reference Figure 1-3A high-anti-interference long-distance pH measurement system includes: a composite pH electrode bulb, a first lead connected to the composite pH electrode bulb and an Ag / AgCl reference electrode, a second lead connected to the Ag / AgCl reference electrode, a shielding layer sleeved on the outside of the second lead and the second reference electrode, the lead of the second reference electrode is connected to the outer shielding layer; a common-mode suppression shielding drive circuit, an impedance conversion circuit and a modulation and demodulation circuit; the first lead and the second lead are connected to the common-mode suppression shielding drive circuit and the impedance conversion circuit, and the outer shielding layer is connected to the modulation and demodulation circuit.

[0020] Furthermore, the first lead is connected to a first high-impedance input operational amplifier N1, which is connected in series with a third resistor R3, which is connected in series with a sixth resistor R6. The sixth resistor R6 is connected in parallel with a first capacitor C1 and a differential amplifier N3. A first resistor R1 is connected in parallel between the first high-impedance input operational amplifier N1 and the third resistor R3, which is connected in series with a second resistor R2. A shield driver N4 is connected in parallel between the first and second resistors R1 and R2. The output of the shield driver N4 is connected to a shielding layer. A fourth resistor R4 is connected in parallel with the second resistor R2, which is connected in series with a second high-impedance input operational amplifier N2. The non-inverting input of the second high-impedance input operational amplifier N2 is connected to a second lead. A fifth resistor R5 is connected in series with the fourth resistor R4, which is connected to ground. Because the pH electrode has extremely high internal resistance and a relatively weak signal, even small external disturbances can significantly affect the electrode signal if the glass bulb leads are not treated. Therefore, a polytetrafluoroethylene sleeve is required around the bulb leads to prevent external leakage current interference. When the lead is long, the lead equivalent circuit is as shown in the following figure. Figure 2 As shown. Rs1 and Rs2 are the internal resistance of the lead, and the shielding layer is usually grounded. In this case, the second capacitor C2 and the third capacitor C3 are the equivalent capacitances of the lead and the shielding layer. When Rs1C2≠Rs2C3, a voltage difference will be generated between Rs1 and Rs2 under the action of the common-mode signal Uic, generating a differential-mode input to the next-level circuit, reducing the common-mode suppression capability. As the lead distance increases, it is very difficult to accurately maintain Rs1C2=Rs2C3. Therefore, the present invention connects the two output ends of the first high-resistance input operational amplifier N1 and the second high-resistance input operational amplifier N2 through the first resistor R1 and the second resistor R2, and the middle connection point of the first resistor R1 and the second resistor R2 outputs a differential voltage Uid. This differential voltage Uid is output to a precision voltage follower, and the output of the precision voltage follower is connected to the inner shielding layer, which is called a shield driver N4. Since the first high-impedance input operational amplifier N1 and the second high-impedance input operational amplifier N2 also form a voltage follower, and since R1=R2, Uid=Uic, the common-mode voltage between the lead and the shield is 0. Selecting high-precision, low-temperature drift first resistor R1 and second resistor R2 will greatly improve common-mode rejection.

[0021] Furthermore, a differential amplifier N3 is connected in parallel between the fourth resistor R4 and the fifth resistor R5 , a demodulator N6 is connected in series to the differential amplifier N3 , and an output end of the demodulator N6 may be connected to a voltage acquisition circuit.

[0022] Since the glass bulb pH electrode and the Ag / AgCl reference electrode are both connected to a high input impedance operational amplifier, they are both in a floating state at this time and a second reference electrode needs to be introduced to provide them with a reference potential. The present invention uses a platinum sheet C2 as the second reference electrode. The lead of the second reference electrode is connected to the outer shielding layer, and another layer of shielding can be added to the first lead of the pH electrode and the second lead of the reference electrode to improve the anti-interference ability. The second reference electrode C2 can be connected to a fixed DC potential. Since the internal resistance of the glass electrode is very large, the DC signal is easily interfered by the outside world. Therefore, the present invention uses PWM wide pulse modulation on the second reference electrode using a modulation and demodulation method. The modulation signal is a positive and negative alternating square wave signal with a duty cycle of 50%. After PWM modulation, the signals of the composite pH electrode bulb and the Ag / AgCl reference electrode are also positive and negative alternating square wave signals. The output is sent to the differential amplifier N3 through a high-impedance operational amplifier. The differential amplifier N3 will output a square wave signal with a DC bias. After the demodulator, the signal outputs a DC level, which is the potential difference between the composite pH electrode bulb and the first reference electrode. The DC potential is different for pH solutions of different concentrations. After being collected by a high-precision voltage collector, relevant calculations can be performed.

[0023] The present invention uses a Leici 991 online composite pH electrode, wired in accordance with the present invention, and connected to the detection circuit and modulation and demodulation circuit of the present invention. The wiring used for the test was 30 meters long, and the electrode was placed near the pond aeration pump. The measured pH value was 7.89 when the pump was not turned on, and fluctuated by ±0.02 pH when the pump was turned on. Swinging the leads revealed no significant fluctuations in the electrode reading. After subsequent data processing, the electrode reading remained stable, demonstrating the present invention's particularly significant long-distance interference resistance.

[0024] The number of devices and processing scales described herein are intended to simplify the description of the present invention, and applications, modifications, and variations of the present invention will be apparent to those skilled in the art.

[0025] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the figures shown and described herein.

Claims

1. A high-anti-interference long-distance pH measurement system, characterized in that: include: A composite pH electrode bulb (1), a first lead (11) connected to the composite pH electrode bulb (1) and an Ag / AgCl reference electrode (2), a second lead (21) connected to the Ag / AgCl reference electrode (2), a shielding layer (3) sleeved on the outside of the second lead (21), and a second reference electrode (4), wherein the lead of the second reference electrode (4) is connected to an outer shielding layer (5); Common mode rejection shielding driving circuit, impedance conversion circuit and modulation and demodulation circuit; The first lead (11) and the second lead (21) are connected to the common mode suppression shielding driving circuit and the impedance conversion circuit, and the outer shielding layer (5) is connected to the modulation and demodulation circuit; The first lead (11) is connected to a first high-impedance input operational amplifier, the first high-impedance input operational amplifier is connected in series with a third resistor, the third resistor is connected in series with a sixth resistor, and the sixth resistor is connected in parallel with a first capacitor and a differential amplifier; A first resistor is connected in parallel between the first high-impedance input operational amplifier and the third resistor, a second resistor is connected in series with the first resistor, a shield driver is connected in parallel between the first resistor and the second resistor, and an output end of the shield driver is connected to a shielding layer (3); The second resistor is connected in parallel with a fourth resistor, the fourth resistor is connected in series with a second high-impedance input operational amplifier, the non-inverting input terminal of the second high-impedance input operational amplifier is connected to a second lead (21), the fourth resistor is connected in series with a fifth resistor, and the fifth resistor is connected to a ground wire; A differential amplifier is connected in parallel between the fourth resistor and the fifth resistor, a demodulator is connected in series to the differential amplifier, and an output terminal of the demodulator is connected to a voltage acquisition circuit.

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