A high source resistance measuring device

Abstract

The application discloses a high source internal resistance measuring device and method, the device comprises a probe connecting module, a sampling module and an AD conversion module which are electrically connected in sequence, and further comprises a double-path temperature calibration compensation module for compensating the influence of temperature change on measuring accuracy, and a filter for eliminating signal fluctuation caused by stirring a liquid to be measured. The high source internal resistance measuring device and method have the advantages of high detection resolution, strong anti-interference capability and high stability.

Description

Technical Field

[0001] This invention relates to a high source internal resistance measuring device, belonging to the field of titration detection technology. Background Technology

[0002] Titration detection includes three types: photometric detection, temperature detection, and potential detection. Among them, potential detection uses a potential titration probe. The potential titration probe has high internal resistance, which results in a very small measurement current. A special measuring device is required to measure its electrode signal. This measuring device is called a potential measuring device, also known as a high source internal resistance measuring device.

[0003] While traditional potential measurement devices can achieve a resolution on the order of 0.1 mV, with the development of electrode technology, liquid feeding technology, sample pretreatment technology, ultra-high resolution temperature measurement technology, and the improvement of testing standards, this detection resolution can no longer fully meet the accuracy requirements.

[0004] Furthermore, traditional potential measurement devices have poor stability, especially in terms of resistance to temperature changes, resulting in significant fluctuations.

[0005] Therefore, it is necessary to design a high source internal resistance measurement device with higher resolution and stronger stability. Summary of the Invention

[0006] To overcome the above problems, the inventors have conducted intensive research and have provided a high source internal resistance measuring device for measuring the electrode signal output by a potentiometric titration probe, comprising a probe connection module, a sampling module and an AD conversion module connected in sequence.

[0007] Preferably, the sampling module includes an amplifier, a sampling resistor, and a closed-loop stabilization control module for the operating voltage.

[0008] Preferably, the working voltage closed-loop stabilization control module adopts an output voltage detection feedback control method to ensure that the working voltage fluctuation range is less than 0.001mV.

[0009] Preferably, the high source internal resistance measuring device further includes a dual-channel temperature calibration and compensation module for compensating for the impact of temperature changes on measurement accuracy.

[0010] Preferably, the dual-channel temperature calibration and compensation module includes a temperature acquisition unit, a processing unit, and a storage unit.

[0011] The temperature acquisition unit measures the temperature of the amplifier and AD conversion chip in the sampling module and transmits the measured temperature to the temperature acquisition unit.

[0012] The storage unit stores a temperature compensation coefficient, which is obtained by calibrating a high source internal resistance measuring device.

[0013] The arithmetic unit performs temperature compensation calculations on the digital signal converted by the AD conversion chip based on the measured amplifier temperature, AD conversion chip temperature, and temperature compensation coefficient in the storage unit to obtain the calibration result.

[0014] Preferably, the high source internal resistance measuring device further includes a filter to eliminate signal fluctuations caused by stirring the liquid to be tested.

[0015] Preferably, the filter is an adaptive filter with two inputs: an input signal and a reference signal. The input signal is the digital signal output by the AD conversion chip, and the reference signal is the motor control signal of the stirrer.

[0016] On the other hand, the present invention also provides a method for measuring high source internal resistance, characterized in that it includes:

[0017] Acquire the potential probe electrode signal;

[0018] The electrode signal is amplified and sampled to obtain the amplified voltage;

[0019] Convert the amplified voltage into a digital signal.

[0020] The beneficial effects of this invention include:

[0021] (1) High detection resolution, with a detection resolution of less than 0.01mV;

[0022] (2) It has strong anti-interference ability and is less affected by temperature;

[0023] (3) High stability, with a stability requirement of ±0.03mV. Attached Figure Description

[0024] Figure 1 A schematic diagram of the overall structure of a high source internal resistance measuring device according to a preferred embodiment of the present invention is shown.

[0025] Figure 2 This diagram illustrates the structure of a sampling module of a high source internal resistance measuring device according to a preferred embodiment of the present invention.

[0026] Figure 3 A schematic diagram of the control flow of the closed-loop stabilization control module for the operating voltage of a high source internal resistance measuring device according to a preferred embodiment of the present invention is shown.

[0027] Figure 4 A schematic diagram of the dual-channel temperature calibration and compensation module of a high source internal resistance measuring device according to a preferred embodiment of the present invention is shown.

[0028] Figure 5A schematic diagram of an adaptive filter for a high source internal resistance measurement device according to a preferred embodiment of the present invention is shown.

[0029] Figure 6 A schematic diagram of the circuit structure of the closed-loop stabilization control module for the operating voltage of a high source internal resistance measuring device according to a preferred embodiment of the present invention is shown.

[0030] Figure 7 The fluctuation of the titration measurement signal is shown. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Through these descriptions, the features and advantages of the present invention will become clearer and more apparent.

[0032] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated otherwise.

[0033] This invention provides a high-source internal resistance measuring device for measuring the electrode signal output by a potentiometric titration probe during potentiometric titration, particularly for measuring chemical electrode signals with high internal resistance characteristics, such as... Figure 1 As shown, it includes a probe connection module, a sampling module, and an AD conversion module.

[0034] Traditional pH meter calibrators can only achieve a resolution on the order of 0.1mV. The inventors discovered through research that the main reason for further improving the resolution is the current interference in the sampling circuit.

[0035] The probe used for potentiometric titration is an electrochemical measurement probe. When the electrochemical measurement probe measures the potential, the output impedance can reach 1GΩ to 3GΩ. Due to such high internal resistance, a very small measurement current is required. The measurement current is generally in the femtoampere range. Such a small measurement current makes the signal transmission path and sampling module very susceptible to interference during the measurement process. Therefore, traditional measurement devices are difficult to achieve more accurate measurements.

[0036] In this invention, based on the inventor's above-mentioned findings, a unique design was made for the probe connection module and the sampling module.

[0037] Specifically, the probe connection module is used to connect the sampling module to the electrodes of the potentiometric titration probe.

[0038] Weak voltage amplification and acquisition control are key to improving the sensitivity and resolution of measurement results. In this invention, for the weak current signal of the potential probe, a sampling resistor is used in the sampling module to realize the conversion between current and voltage, and then amplification and sampling are performed.

[0039] Specifically, the circuit structure of the sampling module is as follows: Figure 2 As shown, the circuit includes amplifier U1 and sampling resistor R1. Amplifier U1, which amplifies the signal gain, is preferably an instrument-specific integrated amplifier, such as AD620. The amplification gain of the circuit is controlled by the resistance value of resistor R4. The signal is output to the AD conversion chip after passing through the amplifier.

[0040] Furthermore, in order to improve the accuracy of the detection signal, eliminate external interference, increase the repetition of the detection process, and overcome the temperature drift and nonlinearity of the system output stage, this invention adopts an output voltage detection feedback control method, and stabilizes the output working voltage through a working voltage closed-loop stabilization control module.

[0041] Preferably, the operating voltage closed-loop stabilization control module includes a CS5460A chip, and its circuit structure is as follows: Figure 6 As shown, the CS5460A is a CMOS monolithic power measurement chip with an active power calculation engine, which can realize system calibration function.

[0042] Furthermore, the term "stable operating voltage" means that the operating voltage fluctuation range is less than 0.001mV.

[0043] Furthermore, in this invention, the working voltage closed-loop stabilization control module operates as follows: Figure 3 As shown, the output voltage is adjusted by feedback through the system setting reference signal, the system operating noise signal, and the output voltage.

[0044] Specifically, the system sets the reference signal R(s), the system operating noise signal N(s), and the output voltage V(s) as the signal sources for the output voltage feedback control submodule. The output voltage feedback control submodule generates an adjustable voltage, which is then calculated by the control object transfer function to obtain the working output voltage.

[0045] Among them, the system setting reference signal R(s) is the output operating voltage setting signal, which can be set arbitrarily within the range of 0.000mV to 1000.000mV;

[0046] The output voltage feedback control submodule adopts a typical PID control strategy. Its PID controller consists of a proportional unit (P), an integral unit (I), and a derivative unit (D). Based on the signal source and the actual output value, the control deviation is formed. The deviation is linearly combined according to the proportional, integral, and derivative values ​​to form the control quantity, which controls the working output voltage signal.

[0047] Preferably, the transfer function of the output voltage feedback control submodule is:

[0048] C(s) = kp[1 + 1 / (TI*s) + TD*s]

[0049] Where kp is the proportionality coefficient; TI is the integral time constant; and TD is the derivative time constant;

[0050] The control object transfer function H(s) is:

[0051] H(s) = G(s) * B(s)

[0052] Wherein, G(s) is the transfer function generated by the variable voltage, and B(s) is the working transfer function of the biochemical reactor. In this invention, the specific forms of G(s) and B(s) are not particularly limited, and those skilled in the art can choose them based on experience, for example, by determining them through the critical proportionality method.

[0053] The inventors discovered that in the system's measurement circuit, the presence of a stir bar causes measurement noise due to internal liquid backflow. Furthermore, the presence of a stir bar in the reaction vessel causes changes in the volume and contact surface of the measuring electrodes within the liquid. Additionally, there is a coupling relationship between the biochemical reaction current and the liquid flow rate; changes in flow rate alter the rate of the biochemical reaction, thus affecting the fluctuations in the measurement signal. Figure 7 As shown, the fluctuation signal generated by the movement of the liquid in the system is displayed in the measurement signal.

[0054] In this invention, by optimizing the conditional PID parameters of the transfer function C(s) of the output voltage feedback control submodule, the fluctuations in the output V(s) signal within the measurement passband are minimized, thereby stabilizing the measurement results and improving the repeatability of the measurement.

[0055] Preferably, in the PID parameters, kp = 10–30%, TI = 10–300s, and TD = 1–100s.

[0056] Any insulator with finite resistance in contact with a high-impedance conductor will generate error current. The inventors discovered that the insulating substrate in the sampling module is the largest source of error in the measuring device. All insulating materials exhibit dielectric relaxation (also known as dielectric absorption or wetting), which limits the performance of electrometer circuits that need to be built up to several fA levels. The insulating substrate is typically made of glass epoxy resin; however, glass epoxy sheets require one hour to dissipate the dielectric relaxation current below 10 fA, indicating that glass epoxy sheets are unsuitable for high-performance electrometer circuits.

[0057] According to the present invention, the insulating base plate of the sampling module is made of a high-frequency board material with low dielectric loss. The low dielectric loss refers to a board material with a loss of less than 0.003, such as an OGERS high-frequency board circuit board, preferably the Rogers 6000 series. In the present invention, it can provide excellent insulation and high-frequency performance, which helps to improve the accuracy of high source internal resistance measurement.

[0058] During potential measurement, the high internal resistance of the electrodes makes the analog voltage highly susceptible to environmental influences and prone to measurement errors. The AD conversion module converts the voltage amplified by the sampling module into a digital signal.

[0059] In this invention, the specific model of the AD conversion chip is not particularly limited. Those skilled in the art can select from any known chip with AD conversion function according to actual needs, such as CS5460A, etc.

[0060] Furthermore, the inventors discovered that temperature drift in the amplifier and AD conversion chip in the sampling module can adversely affect measurement accuracy. In order to achieve high-precision measurement within the normal operating temperature range, the measuring device in this invention also includes a dual-channel temperature calibration compensation module.

[0061] The dual-channel temperature calibration and compensation module includes a temperature acquisition unit, a processing unit, and a storage unit, such as... Figure 4 As shown.

[0062] The temperature acquisition unit is used to measure the temperature of the amplifier and the AD conversion chip in the sampling module. Preferably, the temperature acquisition unit consists of two thermistors, which transmit the acquired amplifier temperature and AD conversion chip temperature to the arithmetic unit.

[0063] The storage unit stores a temperature compensation coefficient, which is obtained by calibrating a high source internal resistance measuring device.

[0064] Specifically, the calibration process is as follows: Before using the high source internal resistance measuring device, the amplifier and AD conversion chip of the measuring device are made to work stably at different temperatures. Multiple fixed voltages are input at the probe connection module to obtain the measurement results corresponding to different temperatures under different fixed voltages, thereby obtaining the temperature compensation coefficient.

[0065] In a preferred embodiment, the plurality of fixed voltages are 0.000mV, 100.000mV, 200.000mV, 500.000mV, 900.000mV, and 1000.000mV, to obtain the corresponding measured values ​​at different temperatures under different voltages. A table is created based on the obtained measured values, or a linear fitting curve is obtained using the least squares method. The compensation coefficient can then be obtained from the fitted curve.

[0066] More preferably, during the compensation stage, when the input voltage is no greater than 1000.000mV, the compensation coefficient is obtained by looking up a table; when the input voltage is greater than 1000.000mV, the compensation coefficient is obtained based on the fitted curve, thereby ensuring the accuracy of the compensation coefficient.

[0067] The arithmetic unit performs temperature compensation calculations on the digital signal converted by the AD conversion chip based on the measured amplifier temperature, AD conversion chip temperature, and temperature compensation coefficient in the storage unit, and obtains the final temperature-compensated calibration result.

[0068] When measuring mixed liquids, the potential probe electrode requires stirring with a stirrer, which alters the contact area between the measuring motor and the liquid. Simultaneously, there is a coupling relationship between the biochemical reaction current and the liquid flow rate. Changes in flow rate alter the rate of the biochemical reaction, thus affecting fluctuations in the measurement signal. Therefore, signal filtering is necessary to eliminate these effects.

[0069] Traditional filtering methods are mostly linear or nonlinear, such as mean filters. However, the effective signal resolution after filtering is low. In this invention, an adaptive filter is set in the computing unit to eliminate interference noise caused by stirring.

[0070] Preferably, the digital signal output by the AD conversion chip is filtered before temperature compensation to improve detection accuracy.

[0071] Adaptive filters are filtering methods developed based on the theories of Kalman and Wiener filters, and are particularly suitable for non-stationary random signals. In this invention, the algorithm block diagram for processing signals by the adaptive filter is as follows: Figure 5 As shown, it has two inputs: an input signal and a reference signal. The input signal is the digital signal output by the AD conversion chip, and the reference signal is the motor control signal of the stirrer.

[0072] Since the control period of the motor control signal of the agitator is the same as the period of the signal fluctuation component, the signal data with the same amplitude as the measured signal can be obtained by transformation, thereby achieving simple, fast, real-time and highly adaptable effective signal discrimination.

[0073] In a more preferred embodiment, the update coefficients of the adaptive filter can be expressed as:

[0074]

[0075] Where w(t) represents the filter update coefficient, t represents time, μ represents the adjustment factor, γ is a constant, e(t) represents the estimation error, and x(t) represents the input data vector.

[0076] This adaptive filter can improve signal resolution by an order of magnitude.

[0077] On the other hand, the present invention also provides a method for measuring high source internal resistance, preferably implemented by the above-mentioned high source internal resistance measuring device, comprising:

[0078] Acquire the potential probe electrode signal;

[0079] The electrode signal is amplified and sampled to obtain the amplified voltage;

[0080] Convert the amplified voltage into a digital signal.

[0081] Preferably, the high source internal resistance measurement method further includes:

[0082] Steady calibration and compensation of digital signals; and / or

[0083] Filter the signal.

[0084] When amplifying the electrode signal, a sampling resistor is used to convert between current and voltage before amplification and sampling.

[0085] During amplification, a dedicated integrated amplifier for instruments is used.

[0086] During sampling, the output operating voltage is kept stable, with fluctuations less than 0.001mV.

[0087] Preferably, the output voltage is adjusted by feedback using a system setting reference signal, a system operating noise signal, and the output voltage.

[0088] During the steady calibration and compensation process of digital signals, the digital signals are compensated and calibrated by measuring the temperature of the amplifier and the AD conversion chip and combining it with the temperature compensation coefficient.

[0089] Furthermore, before using the high source internal resistance measuring device, the amplifier and AD conversion chip of the measuring device are made to work stably at different temperatures. Multiple fixed voltages are input at the probe connection module to obtain the measurement results corresponding to different temperatures under different fixed voltages, thereby obtaining the temperature compensation coefficient.

[0090] In a preferred embodiment, the plurality of fixed voltages are 0.000mV, 100.000mV, 200.000mV, 500.000mV, 900.000mV, and 1000.000mV, to obtain the corresponding measured values ​​at different temperatures under different voltages. A table is created based on the obtained measured values, or a linear fitting curve is obtained using the least squares method. The compensation coefficient can then be obtained from the fitted curve.

[0091] More preferably, during the compensation stage, when the input voltage is no greater than 1000.000mV, the compensation coefficient is obtained by looking up a table; when the input voltage is greater than 1000.000mV, the compensation coefficient is obtained based on the fitted curve, thereby ensuring the accuracy of the compensation coefficient.

[0092] During the signal filtering process, an adaptive filter is used. The input signal of the adaptive filter is the digital signal output by the AD conversion chip, and the reference signal is the motor control signal of the stirrer.

[0093] Preferably, the update coefficients of the adaptive filter can be expressed as:

[0094]

[0095] The high source internal resistance measuring device provided by the present invention can measure the signal output by the potentiometric titration probe in the range of 2500mV, and the measurement stability can be controlled within 0.02mV and the measurement resolution can be controlled within 0.005mV. Its measurement stability and measurement resolution are significantly better than those of traditional measuring devices.

[0096] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front," and "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship in the working state of this invention, and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0097] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0098] The present invention has been described above with reference to preferred embodiments; however, these embodiments are merely exemplary and illustrative. Various substitutions and modifications can be made to the present invention based on these embodiments, all of which fall within the scope of protection of the present invention.

Claims

1. A high-source internal resistance measuring device for measuring the electrode signal output by a potentiometric titration probe, characterized in that, It includes a probe connection module, a sampling module, and an AD conversion chip that are electrically connected in sequence; The sampling module includes an amplifier, a sampling resistor, and a closed-loop stabilization control module for the operating voltage. The closed-loop stabilization control module for the operating voltage adjusts the output voltage based on the system reference signal, system operating noise signal, and output voltage. An output voltage feedback control submodule is configured, using the system reference signal, system operating noise signal, and output voltage as signal sources. This submodule generates an adjustable voltage, which is then calculated using the control object transfer function to obtain the operating output voltage. The output voltage feedback control submodule adopts a PID control strategy, and its transfer function C(s) is: C(s) = kp[1 + 1 / (TI*s) + TD*s] Where kp is the proportionality coefficient; TI is the integral time constant; and TD is the derivative time constant; The control object transfer function H(s) is: H(s) = G(s) * B(s) Where G(s) is the transfer function generated by the variable voltage, and B(s) is the working transfer function of the biochemical reactor; The high source internal resistance measuring device also includes a filter to eliminate signal fluctuations caused by stirring the liquid to be tested; The filter is an adaptive filter with two inputs: an input signal and a reference signal. The input signal is the digital signal output by the AD conversion chip, and the reference signal is the motor control signal of the stirrer.

2. The high source internal resistance measuring device according to claim 1, characterized in that, The working voltage closed-loop stabilization control module uses output voltage detection feedback control to ensure that the working voltage fluctuation range is less than 0.001mV.

3. The high source internal resistance measuring device according to claim 1, characterized in that, The high source internal resistance measuring device also includes a dual-channel temperature calibration and compensation module, which is used to compensate for the impact of temperature changes on measurement accuracy.

4. The high source internal resistance measuring device according to claim 3, characterized in that, The dual-channel temperature calibration and compensation module includes a temperature acquisition unit, a processing unit, and a storage unit. The temperature acquisition unit measures the temperature of the amplifier and the AD conversion chip, and transmits the measured temperature to the temperature acquisition unit; The storage unit stores a temperature compensation coefficient, which is obtained by calibrating a high source internal resistance measuring device. The arithmetic unit performs temperature compensation calculations on the digital signal converted by the AD conversion chip based on the measured amplifier temperature, AD conversion chip temperature, and temperature compensation coefficient in the storage unit to obtain the calibration result.

5. A method for measuring high source internal resistance, using the high source internal resistance measuring device described in any one of claims 1-4, characterized in that, include: Acquire the electrode signal of the potentiometric titration probe; The electrode signal is amplified and sampled to obtain the amplified voltage; Convert the amplified voltage into a digital signal.

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