Automatic calibration system for platinum resistor detection circuit

Abstract

The invention discloses an automatic calibration system for a platinum resistor detection circuit, which is composed of a platinum resistor detection circuit to be calibrated and a calibration circuit, the platinum resistor detection circuit uses a voltage division method to measure the resistance, the calibration circuit uses a digital potentiometer to simulate the platinum resistance value, and the two circuits both use a single-chip microcomputer as a control core. And data and instruction interaction is carried out through a serial port. According to the application, the resistance value of the calibration resistor can be automatically changed according to a preset program, and the platinum resistor detection circuit records the theoretical values of the plurality of calibration resistors and realizes the resistance-temperature mapping by using a linear interpolation method.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of temperature measurement system calibration, and particularly relates to a platinum resistance detection circuit automatic calibration system. BACKGROUND

[0002] The platinum resistance temperature measurement technology has high reliability, high precision, wide range and strong anti-interference ability, and thus occupies an important position in the industrial, scientific research and civil fields, and becomes the preferred scheme for precise temperature measurement at the medium and high temperature ends. The platinum resistance temperature measurement system is usually composed of a platinum resistance and a platinum resistance detection circuit. The platinum resistance detection circuit mainly realizes signal conditioning through a Wheatstone bridge, converts the bridge voltage signal into a digital signal by using an ADC module of a single-chip microcomputer, and then realizes temperature data conversion based on a temperature-resistance table.

[0003] Since the balance of the bridge is a prerequisite for accurate measurement of the platinum resistance temperature measurement system, a variable resistor is usually manually adjusted to balance the bridge. This method has low automation degree and low calibration efficiency. Therefore, an automatic calibration method is needed to make the calibration process more efficient and accurate, and further promote the application of platinum resistance in extreme environments such as high temperature and high vibration. SUMMARY

[0004] The purpose of the present application is to overcome the problems of the prior art. A platinum resistance detection circuit automatic calibration system is disclosed. The system is composed of a platinum resistance detection circuit to be calibrated and a calibration circuit. The platinum resistance detection circuit uses a voltage division method to measure resistance, and the calibration circuit uses a digital potentiometer to simulate the platinum resistance value. Both circuits use a single-chip microcomputer as the control core and exchange data and instructions through a serial port. The resistance value of the calibration resistor can be automatically changed according to the predetermined program by using the present application. The platinum resistance detection circuit records the theoretical values of multiple calibration resistors and realizes the mapping of resistance-temperature by using a linear interpolation method.

[0005] The purpose of the present application is achieved by the following technical solutions: A platinum resistance detection circuit automatic calibration system, comprising: an upper computer, a calibration circuit and a platinum resistance detection circuit to be calibrated. The calibration circuit forms an adjustable resistance control circuit based on the upper computer control, and the platinum resistance detection circuit completes the calibration of itself based on the monitoring of each calibration resistor formed by the calibration circuit.

[0006] According to a preferred embodiment, the calibration circuit comprises a digital potentiometer for simulating the platinum resistance R x at different temperatures. The platinum resistance detection circuit comprises a resistance R0, a voltage source V ref and an ADC chip. The digital potentiometer, resistor and voltage source are connected in series, and the ADC chip is configured to complete the voltage U across the digital potentiometer x The resistance value of the digital potentiometer is measured by the voltage divider method.

[0007] According to a preferred embodiment, the platinum resistance detection circuit further comprises a first single-chip microcomputer, and the calibration circuit further comprises a second single-chip microcomputer; The upper computer is connected to the first single-chip microcomputer in a wired and / or wireless manner, and the first single-chip microcomputer is connected to the second single-chip microcomputer through a serial port; The first single-chip microcomputer calculates the resistance value of the digital potentiometer based on the voltage measured by the ADC chip; and the second single-chip microcomputer is configured to complete the adjustment of the digital potentiometer based on the instructions of the upper computer to form each calibration resistor.

[0008] According to a preferred embodiment, the automatic calibration process of the platinum resistance detection circuit comprises: a) The upper computer sends a calibration instruction to the platinum resistance detection circuit; b) After receiving the calibration instruction, the platinum resistance detection circuit enters the calibration process and then sends the resistance value R1 of the calibration point to the calibration circuit; c) After receiving the resistance instruction of the calibration point, the calibration circuit adjusts the resistance of the digital potentiometer to the corresponding resistance value; d) The platinum resistance detection circuit records the current measured resistance value ; e) Repeat steps b) to d) to adjust the resistance value of the digital potentiometer at each calibration point and measure the resistance at each calibration point .

[0009] According to a preferred embodiment, the resistance value of the calibration point is determined based on the temperature measurement range of the analog platinum resistance.

[0010] According to a preferred embodiment, the corrected resistance value calculated by the platinum resistance detection circuit after calibration is:

[0011] In the formula, n is the index of the calibration point, is the corrected platinum resistance value at any temperature, is the platinum resistance value measured based on the ADC chip, is the true resistance value at the n-th calibration point temperature, which is also the adjustment value of the digital potentiometer; is the measured resistance value of the resistance at the n-th calibration point temperature, which is the measured resistance value of the platinum resistance detection circuit.

[0012] According to a preferred embodiment, when the platinum resistance detection circuit is used for temperature measurement, First, the platinum resistance value is measured by using a platinum resistance detection circuit to correct the resistance value. After obtaining the corrected resistance value, the actual temperature at the corresponding resistance value can be obtained by using the temperature-resistance comparison table of the platinum resistance, thus completing the actual temperature measurement.

[0013] The aforementioned main solution and its various further alternative solutions can be freely combined to form multiple solutions, all of which are solutions that can be adopted and are claimed in this application. Those skilled in the art, after understanding the solution of this application, will realize that there are many combinations based on the prior art and common general knowledge, all of which are technical solutions to be protected in this application, and will not be exhaustively listed here.

[0014] The beneficial effects of this application are: a) The calibration process is highly automated. The entire calibration process is implemented through software, eliminating the need for manual intervention in intermediate processes and making it easy to implement assembly line operations. b) High temperature measurement accuracy: High-precision temperature measurement can be achieved by selecting multiple calibration points and combining linear interpolation. c) The calibration system has low cost. The calibration circuit consists only of a microcontroller, a digital potentiometer, and peripheral interface circuits, resulting in low cost and long service life. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the principle structure of the automated calibration system for platinum resistance testing circuits in this application. Detailed Implementation

[0016] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, unless otherwise specified, the following embodiments and features in the embodiments can be combined with each other.

[0017] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0018] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this application is in use. They are only for the convenience of describing this application 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 on this application. In addition, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0019] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0020] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" 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 connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0021] Furthermore, it should be noted that unless otherwise specified in this application, the specific structures, connections, positions, power sources, etc. involved are all things that a person skilled in the art can know without creative effort based on the prior art.

[0022] Figure 1 The schematic diagram illustrates the principle structure of an automated calibration system for platinum resistance thermometer circuits, such as... Figure 1 As shown, this application discloses an automated calibration system for a platinum resistance thermometer circuit. The automated calibration system includes a host computer, a calibration circuit, and a platinum resistance thermometer circuit to be calibrated. The calibration circuit forms an adjustable resistor control circuit based on the control of the host computer. The platinum resistance thermometer circuit completes its own calibration based on monitoring the calibration resistors formed by the calibration circuit.

[0023] Preferably, the calibration circuit includes a digital potentiometer, which is used to simulate the platinum resistance R at different temperatures. x The platinum resistance detection circuit includes: a resistor R0 and a voltage source V.ref The ADC chip, the digital potentiometer, the resistor, and the voltage source are connected in series. The ADC chip is configured to output a voltage U across the digital potentiometer. x The resistance value of the digital potentiometer is measured by voltage divider method.

[0024] Furthermore, the platinum resistance detection circuit further includes a first microcontroller, and the calibration circuit further includes a second microcontroller; the host computer and the first microcontroller are connected and communicate via wired and / or wireless means, and the first microcontroller is connected to the second microcontroller via a serial port; the first microcontroller calculates the resistance value of the digital potentiometer based on the voltage measured by the ADC chip; the second microcontroller is configured to adjust the digital potentiometer based on the instructions of the host computer to form each calibration resistor.

[0025] The process of measuring the resistance of a platinum resistance thermometer using the voltage divider method is as follows: The microcontroller can then obtain the corresponding temperature using the temperature-resistance comparison table for platinum resistance thermometers.

[0026] Preferably, calibration is required because the voltage source and resistor in the platinum resistance thermometer detection circuit have errors. The calibration circuit uses a digital potentiometer to simulate platinum resistance thermometers at different temperatures. The second microcontroller in the calibration circuit controls the digital potentiometer through a digital interface (such as I2C or SPI), thereby realizing software adjustment of the resistance and replacing the manual adjustment of the variable resistor box for calibration.

[0027] Specifically, the automatic calibration process for the platinum resistance thermometer circuit includes: a) The host computer sends a calibration command to the platinum resistance thermometer circuit; b) After receiving the calibration command, the platinum resistance detection circuit enters the calibration process and then sends the resistance value R1 of the calibration point to the calibration circuit. c) After receiving the resistance command from the calibration point, the calibration circuit adjusts the resistance of the digital potentiometer to the corresponding value. d) The platinum resistance detection circuit records the currently measured resistance value. ; e) Repeat steps b) to d) to adjust the resistance value of the digital potentiometer at each calibration point and measure the resistance at each calibration point. .

[0028] Furthermore, the resistance values ​​at the calibration points are determined based on the temperature measurement range of the simulated platinum resistance thermometer. Specifically, the number of temperature calibration points is determined according to the temperature measurement range and accuracy; the higher the temperature measurement accuracy, the more calibration points are required. Typically, within the temperature measurement range, the resistance values ​​of the simulated platinum resistance thermometer at different temperatures are uniformly selected as the calibration resistance values, taking into account the resolution of the digital potentiometer. The calibration resistance values ​​can be obtained from a platinum resistance temperature lookup table, forming a set (temperature T1, resistance R1), ..., (temperature T...). nresistance R n The calibration point.

[0029] Preferably, the corrected resistance value of the platinum resistance detection circuit, calculated using a linear interpolation method after calibration, is as follows:

[0030] In the formula, n is the index of the calibration point. The corrected resistance value of the platinum resistance thermometer at any temperature. The resistance value of the platinum resistance thermometer is obtained based on the measurement using an ADC chip. This is the actual resistance value at the nth calibration point temperature, and also the adjustment value of the digital potentiometer; The measured resistance value at the nth calibration point temperature is the same as the measured resistance value of the platinum resistance detection circuit.

[0031] Preferably, when using a platinum resistance thermometer circuit for temperature measurement, the resistance value of the platinum resistance thermometer is first corrected using the platinum resistance thermometer circuit. Measurements were taken to obtain the corrected resistance value. Subsequently, the actual temperature at the corresponding resistance value can be obtained by using the temperature-resistance comparison table of the platinum resistance thermometer, thus completing the actual temperature measurement.

[0032] Example 1 The technical solution of this application is illustrated by the following embodiment: a platinum resistance thermometer (PT1000) is used as the temperature sensing element. The platinum resistance thermometer detection circuit uses an STM32F107 chip as the main control microcontroller, i.e., the first microcontroller, and an ADS1258 as the ADC chip (with a resolution of up to 24 bits) to detect the voltage across the PT1000 resistor. V x A MAX6164A reference voltage chip (4.096V) is used as the reference voltage for the ADC, and a 2K ohm resistor is connected in series to power the platinum resistance, forming a voltage divider circuit for measuring resistance. The microcontroller reads the data from the ADC chip through the SPI interface.

[0033] The calibration circuit uses an STM32F107 chip as the main control microcontroller, i.e., the second microcontroller, and an AD5259 digital potentiometer chip as the standard resistor for simulating platinum resistance. The second microcontroller controls the resistance value of the digital potentiometer through an I2C interface.

[0034] After the platinum resistance thermometer detection circuit starts the calibration program, it controls the microcontroller of the calibration circuit to adjust the resistance value of the digital potentiometer through serial port commands.

[0035] Within the measurement range of -60℃ to 150℃, the resistance at three temperature points—low temperature (-50℃), medium temperature (25℃), and high temperature (120℃)—is selected as calibration points. The platinum resistance detection circuit records the measured resistance at -50℃, 25℃, and 120℃ respectively according to the calibration procedure. The measured resistance can be calculated by voltage division, and the calculation formula is shown in (Formula-1).

[0036] (Equation-1) After calibration, the platinum resistance detection circuit can correct the resistance value at any temperature by using the resistance value at the calibration point and combining it with the linear interpolation method. The calculation formula for the corrected resistance measurement result is shown in (Equation-2). Then, the actual temperature is calculated by using the PT1000 resistance-temperature relationship formula (Equation-3). This ensures that the measurement error is within 0.5℃ throughout the entire temperature measurement range. The above process can be fully implemented by software, with a high degree of automation.

[0037] (Equation-2) In the formula: The resistance value of PT1000 measured by the ADC chip at any temperature; The resistance value of the PT1000 after calibration at any temperature; The resistance of the PT1000 was measured at -50℃ at the first calibration point. This is the actual resistance value of the PT1000 at the first calibration point -50℃; Measure the resistance of the PT1000 at 25℃ for the second calibration point; This is the actual resistance value of the PT1000 at the second calibration point at 25℃. Measure the resistance of the PT1000 at 120℃ for the third calibration point; This is the actual resistance value of the PT1000 at the third calibration point of 120℃.

[0038] (Equation 3) The calibration process of this application is highly automated, and the entire calibration process is implemented through software, without the need for manual intervention in the intermediate process, making it easy to achieve assembly line operation; the temperature measurement accuracy of this application is high, and high-precision temperature measurement can be achieved by selecting multiple calibration points and combining linear interpolation; the calibration system of this application has low cost, and the calibration circuit consists only of a microcontroller, a digital potentiometer and peripheral interface circuits, which is low in cost and has a long service life.

[0039] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An automated calibration system for platinum resistance thermometer circuits, characterized in that, The automated calibration system for the platinum resistance thermometer circuit includes: a host computer, a calibration circuit, and a platinum resistance thermometer circuit to be calibrated; The calibration circuit is an adjustable resistor control circuit controlled by a host computer. The platinum resistance detection circuit completes its own calibration based on monitoring the calibration resistors formed by the calibration circuit.

2. The automated calibration system for platinum resistance thermometer circuits as described in claim 1, characterized in that, The calibration circuit includes a digital potentiometer, which is used to simulate a platinum resistance thermometer R at different temperatures. x The platinum resistance detection circuit includes: a resistor R0 and a voltage source V. ref and ADC chip, The digital potentiometer, resistor, and voltage source are connected in series, and the ADC chip is configured to output a voltage U across the digital potentiometer. x The resistance value of the digital potentiometer is measured by voltage divider method.

3. The automated calibration system for platinum resistance thermometer circuits as described in claim 2, characterized in that, The platinum resistance detection circuit further includes a first microcontroller, and the calibration circuit further includes a second microcontroller; The host computer and the first microcontroller are connected and communicate via wired and / or wireless means, and the first microcontroller is connected to the second microcontroller via a serial port; The first microcontroller calculates the resistance value of the digital potentiometer based on the voltage measured by the ADC chip; the second microcontroller is configured to adjust the digital potentiometer based on instructions from the host computer to form each calibration resistor.

4. The automated calibration system for platinum resistance thermometer circuits as described in claim 3, characterized in that, The automatic calibration process for the platinum resistance thermometer circuit includes: a) The host computer sends a calibration command to the platinum resistance thermometer circuit; b) After receiving the calibration command, the platinum resistance detection circuit enters the calibration process and then sends the resistance value R1 of the calibration point to the calibration circuit. c) After receiving the resistance command from the calibration point, the calibration circuit adjusts the resistance of the digital potentiometer to the corresponding value. d) The platinum resistance detection circuit records the currently measured resistance value. ; e) Repeat steps b) to d) to adjust the resistance value of the digital potentiometer at each calibration point and measure the resistance at each calibration point. .

5. The automated calibration system for platinum resistance thermometer circuits as described in claim 4, characterized in that, The resistance value at the calibration point is determined based on the temperature measurement range of the simulated platinum resistance thermometer.

6. The automated calibration system for platinum resistance thermometer circuits as described in claim 4, characterized in that, The corrected resistance value of the platinum resistance detection circuit, calculated using a linear interpolation method after calibration, is as follows: In the formula, n is the index of the calibration point. The corrected resistance value of the platinum resistance thermometer at any temperature. The resistance value of the platinum resistance thermometer is obtained based on the measurement using an ADC chip. This is the actual resistance value at the nth calibration point temperature, and also the adjustment value of the digital potentiometer; The measured resistance value at the nth calibration point temperature is the same as the measured resistance value of the platinum resistance detection circuit.

7. The automated calibration system for platinum resistance thermometer circuits as described in claim 4, characterized in that, When using a platinum resistance thermometer circuit for temperature measurement First, the platinum resistance value is measured by using a platinum resistance detection circuit to correct the resistance value. After obtaining the corrected resistance value, the actual temperature at the corresponding resistance value can be obtained by using the temperature-resistance comparison table of the platinum resistance, thus completing the actual temperature measurement.

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