Platinum resistor temperature measurement circuit and method thereof

Abstract

The invention provides a platinum resistor temperature measurement circuit and a method thereof, and belongs to the technical field of platinum resistor temperature measurement. The method mainly solves the problem of high-precision temperature measurement matched with an inertial measurement unit computer of a certain model. The resistance value of a high-precision platinum resistor Pt1000 in the conditioning circuit changes along with the external temperature, a high-precision constant voltage source provides reference voltage, the Pt1000 platinum resistor is used for building a bridge, the voltage difference of bridge arms of the bridge is amplified through an instrument amplifier and then subjected to A / D conversion and collection, intelligent processing is completed at the rear end through software, an accurate voltage value is collected, and a measured temperature value can be obtained through conversion. The structure and the design method of the circuit are simple, a processing method combining software and hardware is adopted, the acquisition precision is not lower than 0.1 DEG C (including test accuracy and test stability), the measurement range is wide (-70 DEG C to 400 DEG C), and the circuit has the characteristics of high reliability, low cost, low power consumption, full-localization and miniaturization, and has been shaped and used on a plurality of major models of equipment.

Description

Technical Field

[0001] The invention belongs to the technical field of platinum resistance temperature measurement, and in particular relates to a platinum resistance temperature measurement circuit and a method thereof. Background Art

[0002] Platinum resistors are made by sputtering platinum onto a ceramic substrate using vacuum deposition thin film technology. The film thickness is within 2μm. Ni (or Pd) leads are fixed with glass sintering materials and laser trimmed to form thin film elements. Its resistance value will change with temperature, and the temperature of the object being measured can be inferred by measuring its resistance value. The resistance value that is proportional to the change in temperature is called a positive temperature coefficient, and the resistance value that is inversely proportional to the temperature is called a negative temperature coefficient. The resistance value of a platinum resistor at the freezing point of 0°C is called the nominal resistance, and commonly used resistance values ​​are 100Ω, 200Ω, 500Ω, and 1000Ω. For example, a platinum resistor model Pt1000 is a positive temperature coefficient platinum resistor with a nominal resistance of 1000Ω. Its temperature characteristic curve is almost a straight line with good linearity. The relationship between the resistance value and temperature of a platinum resistor is shown in Formula 1: R t =R0(1+ t)…………………………………………(1) Where: t is temperature; R0=1000 , =3.85×10-3 / ℃; The characteristic of platinum resistors is that their resistance changes with temperature, and this characteristic can be used to measure temperature. Platinum resistors are not only widely used in industrial temperature measurement, but are also made into standard reference instruments. Many models of products now have the same measurement requirements. For example, inertial measurement combination equipment needs to measure the temperature of meters, gyroscopes, etc. in real time in order to complete temperature control and ensure product performance. However, most of the temperature measurement circuits based on platinum resistors in China currently use imported IC integrated design methods, or the temperature measurement methods used have uncontrollable acquisition accuracy and cannot meet the requirements of high reliability and high performance. Summary of the invention

[0003] The present invention proposes a platinum resistance temperature measurement circuit and method thereof to solve the technical problem that traditional temperature measurement circuits based on platinum resistance in the prior art mostly use imported IC integrated design methods, the temperature acquisition accuracy is uncontrollable, and the requirements of high reliability and high performance cannot be met.

[0004] In order to achieve the above object, the present invention adopts the following technical solution: A platinum resistance temperature measurement circuit comprises a conditioning circuit and a temperature acquisition module, wherein the temperature acquisition module comprises an AD control module and an AD smoothing module, wherein the input end of the conditioning circuit is connected to a measured channel, the output end of the conditioning circuit is connected to a signal conversion module, and the output end of the signal conversion module is connected to the input end of the temperature acquisition module; A conditioning circuit, used for outputting a voltage signal according to the temperature of the channel being measured; A signal conversion module is used to amplify the voltage signal by multiples and convert it into a serial digital signal; AD control module, used to convert serial data into parallel data and output the collected data after switching the analog switch according to the timing design; The AD smoothing module is used to smooth the collected data and then output the collected results.

[0005] The measured platinum resistor is connected to a reference voltage source to provide a voltage reference of 10V±0.005V for the conditioning circuit. The measured platinum resistor is connected to the measured channel through an external interface to form a conditioning circuit.

[0006] The positive input terminal of the amplifier follower circuit is connected to the output terminal of the conditioning circuit, the negative input terminal is connected in series with a precision current limiting resistor and a reference resistor, and the negative input terminal of the amplifier follower circuit is connected to the voltage of the reference resistor.

[0007] The signal conversion module includes an amplifier-follower circuit, which is used to amplify the voltage signal output by the conditioning circuit by multiples and output the amplified voltage signal.

[0008] The signal conversion module also includes an AD converter, which is used to convert the amplified voltage signal into a serial digital signal.

[0009] The amplifier-follower circuit uses a 620 instrument amplifier with a maximum amplification factor of 130 times. After the voltage signal is amplified, the voltage range of the output end is 4.901V~9.685V.

[0010] The output end of the AD converter is connected to an isolation circuit, and the isolation circuit is used to perform anti-interference isolation on the serial digital signal output by the AD converter.

[0011] A design method for a platinum resistor temperature measurement circuit, wherein a conditioning circuit provides a suitable current to a measured platinum resistor according to the temperature of a measured channel, thereby extracting the voltage of the platinum resistor and outputting a voltage signal corresponding to the temperature of the measured channel; a signal conversion module receives the voltage signal output by the conditioning circuit and converts it into a serial digital signal after amplifying it; the signal conversion module outputs the serial digital signal to an AD control module; the AD control module converts the serial data into parallel data and switches an analog switch according to a timing design, and then outputs the collected data to an AD smoothing module; the AD smoothing module smoothes the collected data and outputs the collected result.

[0012] When the conditioning circuit outputs the voltage signal corresponding to the measured channel, it also outputs a control signal to the temperature acquisition module through the isolation circuit. After receiving the control signal, the temperature acquisition module starts the AD control module and the AD smoothing module.

[0013] The AD smoothing module takes the most recent 8 collected data output by the AD control module, uses a shifting method to iteratively accumulate the data, and then averages and outputs the collected results through a shifting method.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a platinum resistor temperature measurement circuit. In the conditioning circuit, the measured platinum resistor is connected to a high-precision reference voltage source to provide a stable basis for subsequent measurements, so that the output voltage signal can more accurately reflect temperature changes. In the signal conversion module, the voltage signal is first amplified by the amplifier follower circuit to enhance the signal strength and improve the resolution, and then converted into a serial digital signal by the AD converter, reducing the interference and attenuation effects during the transmission of the analog signal. In terms of data processing, the AD control module converts serial data into parallel data to ensure the accuracy of data conversion, and performs analog switch switching according to the timing design to collect signals from various channels in an orderly manner. The AD smoothing module smoothes the collected data, takes the most recent 8 collected data, and uses a shifting method to iteratively accumulate and average the data, effectively reducing the influence of random errors on the measurement results, thereby significantly improving the overall collection accuracy and meeting the requirements of high-precision temperature measurement.

[0015] The circuit design of the present invention has clear division of labor and coordinated work among the circuit modules, and the conditioning circuit, signal conversion module and temperature acquisition module cooperate with each other, thereby improving the stability of the circuit. During the signal transmission process, the serial digital signal output by the AD converter is isolated from interference by the isolation circuit, thereby reducing the influence of external interference on the measurement result, further enhancing the reliability of the circuit, and enabling it to operate stably in a highly reliable device. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 : Structure diagram of platinum resistance temperature measurement circuit; Figure 2 : AD control module principle block diagram; Figure 3 : AD smoothing module principle block diagram; Figure 4 : AD control module timing relationship diagram; Figure 5 : AD control module acquisition timing diagram; Figure 6 : Timing diagram of output signal in cyclic acquisition. DETAILED DESCRIPTION

[0017] In order to further understand the content of the present invention, the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the embodiments are only for explaining the present invention and are not intended to limit it.

[0018] like Figure 1 As shown, it includes a conditioning circuit and a temperature acquisition module. The conditioning circuit is composed of a measured platinum resistor, a high-precision voltage source, a current limiting resistor and a reference resistor. The conditioning circuit is connected to the measured channel through an external interface, and the output end of the conditioning circuit is connected to the amplifier follower circuit through an interface circuit; one end of the measured platinum resistor is connected to the external interface, and the other end is connected to the interface circuit; the current limiting resistor is connected in series with the reference resistor, and the high-precision voltage source provides a 10V voltage for the series circuit of the measured platinum resistor, the current limiting resistor and the reference resistor, and the output end of the amplifier follower circuit is connected with an AD converter; the input positive pole of the amplifier follower circuit is connected to the output end of the conditioning circuit, and the input negative terminal of the amplifier follower circuit is connected in series with the current limiting resistor and the reference resistor, and the input negative pole of the amplifier follower circuit is connected to the voltage of the reference resistor. The output end of the AD converter is connected to the temperature acquisition module through an isolation circuit; the temperature acquisition module includes an AD control module and an AD smoothing module, the output end of the AD control module is connected to the input end of the AD smoothing module, and the output end of the AD smoothing module is connected to the DSP through an EMIF interface. The conditioning circuit also outputs a control signal to the temperature acquisition module through an isolation circuit to start the temperature acquisition module.

[0019] This embodiment proposes a platinum resistor temperature measurement circuit, which uses a 581 type 10V reference high-precision voltage source to provide a high-precision (10V±0.005V) voltage reference, and provides the voltage to a current-limiting resistor with a resistance of 39K and a measured platinum resistor. When the measured temperature is -40°C~80°C, a suitable current is provided to the measured platinum resistor, so that the voltage of the platinum resistor is extracted for the back-end acquisition channel; the current passing through the platinum resistor is about 0.248mA~0.251mA, and the voltage variation range of this point is 212.3mV~324.5mV. The output end of the conditioning circuit outputs a voltage signal corresponding to the temperature of the measured channel to the amplifier follower circuit through the interface circuit; at the same time, the conditioning circuit also outputs a control signal to the temperature acquisition module through the interface circuit and the isolation circuit. After receiving the control signal, the temperature acquisition module starts the AD control module and the AD smoothing module. When there are multiple channels under test, the output voltage signal is designed according to this method, and the multiple channels under test are switched by using an analog switch, and provided to the back-end temperature acquisition system through the interface circuit; in this embodiment, the amplifier follower circuit uses a 620-type instrument amplifier, and the voltage signal is amplified by using the 620-type instrument amplifier. The positive input terminal of the 620-type instrument amplifier is connected to the output terminal of the analog switch, and the negative input terminal uses a 39K precision current limiting resistor and a 1.21K reference resistor in series to divide the 10V reference source. The negative input terminal of the 620-type instrument amplifier is connected to the voltage value of the 1.21K reference resistor, and the voltage difference between the positive and negative terminals is -37.7mV~74.5mV. The maximum amplification factor of the 620-type instrument amplifier is 130 times, and the voltage range of the output terminal after the voltage signal is amplified is -4.901V~9.685V. The 620 instrument amplifier outputs the amplified voltage signal to the AD converter, and the AD converter converts the amplified voltage signal into a serial digital signal, which is then sent to the temperature acquisition module through an isolation circuit to further improve the acquisition accuracy.

[0020] In this embodiment, the AD converter is a 977-type 16-bit A / D converter with an input range of ±10V and an output code system of binary complement, 1LSB=(20V / 2 16 ) = 305μV, the highest bit is the sign bit, 1 represents a negative number, and 0 represents a positive number.

[0021] Algorithm example: 32477 The amplified voltage value V ; The AD control module converts the serial data into parallel data according to the timing instructions in the AD device manual and the serial data output by the 977 AD converter. A large cycle is performed to switch each channel and then output the collected data. The collected data is transmitted to the AD Pinghu module for smoothing and the processing results are output. You can choose whether to start smoothing.

[0022] The AD control module filters the input serial digital signal, and then starts the serial-to-parallel conversion of the SPI control signal output and the output data of the AD converter through the control instructions output by the conditioning circuit, completes the switching of the analog switch according to the designed timing, and then outputs the collected data. The specific schematic diagram is shown in Figure 2 shown.

[0023] The collected data output by the AD control module is the temperature to be measured T, and the calculation method of the temperature to be measured T is: (1) The acquisition result is divided by the gain G of the instrumentation amplifier. The voltage difference before and after amplification: , the voltage difference before and after amplification V1 unit: mV). V=9.911 ; (2) The conversion formula between differential voltage and resistance value is as follows: , R is the resistance to be measured, unit: Ω; calculate the resistance to be measured R according to this formula; (3) Conversion formula between resistance to be measured and temperature: , T is the temperature to be measured.

[0024] The AD control module continuously outputs the collected data, i.e. the temperature to be measured, to the AD smoothing module. Each collected data enters the AD smoothing module for smoothing. The AD smoothing module takes the average of the latest 8 collected data, uses the shift method to iteratively accumulate the data, and then averages it by shifting. During the smoothing process, the internal result register is not updated, and the external interface is controlled to ensure the stability of the interface data. The principle block diagram of the AD control module is shown in the figure. Figure 3 The AD smoothing module mainly completes data averaging, completes data sliding window according to the output of the AD control module, and finally outputs the temperature average result of the current measured channel to the DSP through the EMIF interface.

[0025] When the AD control module performs serial-to-parallel conversion, the integrated acquisition cycle counter first outputs the conversion start signal AD_RC, and outputs the channel switching signal to the data serial-to-parallel conversion module. After receiving the channel switching signal, the data parallel-to-serial conversion module filters the input clock signal AD_CLK and the conversion data AD_DATA, and then converts the serial data output by the AD converter into parallel data, and then calculates and outputs the parallel data using the above-mentioned calculation method of the temperature to be measured T. The timing relationship is as follows Figure 4 As shown, the AD acquisition timing diagram is as follows Figure 5As shown. The temperature AD channel switches every 2ms. If all channels are enabled, a complete acquisition cycle takes 24ms (calculated based on 12 channels). The acquisition results need to be smoothed in the data processing system (FPGA). The specific requirements are: take 8 acquisition values, average them, and output the processed results. Therefore, it is necessary to wait for at least 192ms after initialization. The standard position does not need smoothing. Due to hardware delay requirements, it is necessary to wait for more than 1.8ms after each channel switching before the acquisition operation can be performed. Each channel sends 2 acquisition (AD_RC) commands, 100us apart, and latches the second acquisition result.

[0026] like Figure 6 As shown in the figure, the output signal timing diagram in the temperature cycle acquisition, the temperature acquisition completes a cycle, and the channel switching order is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 (standard position).

[0027] During data acquisition, AD_DATA is sampled at the rising edge of AD_CLK (to obtain the final valid data of each channel), and then serialized and converted to 16-bit data. The collected data is latched, and the 8 results are averaged after 8 acquisitions, and the processing results are output to the data bus in 16 bits. The data average processing requires that 8 acquisition results of the same channel be latched in sequence, and the 8 acquisition results are averaged. The data update requirement is to remove the earliest data each time, add the latest acquired data, and then perform average calculation. The temperature acquisition function is an intelligent acquisition mode. For the offset address 0x00A03, write 0x"AAAA" to start the conversion, and write 0x"5555" to stop the conversion; the temperature acquisition data address comparison table is shown in Table 1 below. The temperature acquisition system can read back the current analog switch state, and the readback address is 0x00A00, where bit1 corresponds to the analog switch control terminal A0, bit2 corresponds to A1, bit3 corresponds to A2, bit4 corresponds to A3, bit0 corresponds to the EN terminal, and the remaining bits are invalid. The acquisition results are stored in a fixed address and can be read by the DSP at any time.

[0028] Table 1

[0029] By using the platinum resistance temperature measurement circuit design of the present invention, the acquisition accuracy can be achieved to be no less than 0.1°C (including test accuracy and test stability), a wide measurement range (-70°C to 400°C), low power consumption, high reliability, and can be used on high-precision and high-reliability equipment.

[0030] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art should understand that the specific implementation modes of the present invention can still be modified or replaced by equivalents, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A platinum resistance temperature measurement circuit, characterized in that: It includes a conditioning circuit and a temperature acquisition module, the temperature acquisition module includes an AD control module and an AD smoothing module, the input end of the conditioning circuit is connected to the measured channel, the output end of the conditioning circuit is connected to the signal conversion module, and the output end of the signal conversion module is connected to the input end of the temperature acquisition module; A conditioning circuit, used for outputting a voltage signal according to the temperature of the channel being measured; A signal conversion module is used to amplify the voltage signal by multiples and convert it into a serial digital signal; AD control module, used to convert serial data into parallel data and output the collected data after switching the analog switch according to the timing design; The AD smoothing module is used to smooth the collected data and then output the collected results.

2. A platinum resistance temperature measurement circuit according to claim 1, characterized in that: The measured platinum resistor is connected to a reference voltage source to provide a voltage reference of 10V±0.005V for the conditioning circuit. The measured platinum resistor is connected to the measured channel through an external interface to form a conditioning circuit.

3. A platinum resistance temperature measurement circuit according to claim 1, characterized in that: The positive input terminal of the amplifier follower circuit is connected to the output terminal of the conditioning circuit, the negative input terminal is connected in series with a current limiting resistor and a reference resistor, and the negative input terminal of the amplifier follower circuit is connected to the voltage of the reference resistor.

4. A platinum resistance temperature measurement circuit according to claim 1, characterized in that: The signal conversion module includes an amplifier-follower circuit, which is used to amplify the voltage signal output by the conditioning circuit by multiples and output the amplified voltage signal.

5. A platinum resistance temperature measurement circuit according to claim 4, characterized in that: The signal conversion module also includes an AD converter, which is used to convert the amplified voltage signal into a serial digital signal.

6. A platinum resistance temperature measurement circuit according to claim 4, characterized in that: The amplifier-follower circuit uses a 620 instrument amplifier with a maximum amplification factor of 130 times. After the voltage signal is amplified, the voltage range of the output end is 4.901V~9.685V.

7. A platinum resistance temperature measurement circuit according to claim 1, characterized in that: The output end of the AD converter is connected to an isolation circuit, and the isolation circuit is used to perform anti-interference isolation on the serial digital signal output by the AD converter.

8. A method for designing a platinum resistance temperature measurement circuit, based on a platinum resistance temperature measurement circuit according to any one of claims 1 to 8, characterized in that: The conditioning circuit outputs a voltage signal corresponding to the temperature of the measured channel through the measured platinum resistor according to the temperature of the measured channel. The signal conversion module receives the voltage signal output by the conditioning circuit and converts it into a serial digital signal after amplifying it. The signal conversion module outputs the serial digital signal to the AD control module. The AD control module converts the serial data into parallel data and switches the analog switch according to the timing design, and then outputs the collected data to the AD smoothing module. The AD smoothing module smoothes the collected data and outputs the collected result.

9. The method for designing a platinum resistance temperature measurement circuit according to claim 8, characterized in that: When the conditioning circuit outputs the voltage signal corresponding to the measured channel, it also outputs a control signal to the temperature acquisition module through the isolation circuit. After receiving the control signal, the temperature acquisition module starts the AD control module and the AD smoothing module.

10. The design method of a platinum resistance temperature measurement circuit according to claim 9, characterized in that: The AD smoothing module takes the most recent 8 collected data output by the AD control module, uses a shifting method to iteratively accumulate the data, and then averages and outputs the collected results through a shifting method.

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