Multi-channel measuring circuit with software configurable general platinum resistor and thermocouple

Abstract

The invention belongs to the technical field of multi-channel temperature measurement, and particularly relates to a multi-channel measurement circuit with software configurable general platinum resistors and thermocouples. In order to overcome the defects that an existing temperature sensor measurement scheme is low in integration level, low in standardization degree and the like, a novel digital and universal multi-channel temperature sensor measurement microcircuit device is provided, and universal temperature sensor excitation is achieved by designing a programmable bias mode and programmable voltage signal gain; the MCU processor is introduced to realize control of the multi-way switch multiplexer, and accurate measurement of each channel by the ADC is realized; and the MCU realizes configuration and data transmission of each temperature sensor channel through the UART interface. Compared with a temperature sensor signal measurement scheme, the excitation mode, the bias mode and the voltage gain coefficient of the channel can be configured through software to adapt to different types of platinum resistors and thermocouples, and market requirements are met.

Description

Technical Field

[0001] The invention belongs to the technical field of multi-channel temperature measurement, and in particular relates to a multi-channel measurement circuit of a software-configurable universal platinum resistor and a thermocouple. Background Art

[0002] In the current liquid engines, stratospheric environmental control cabins, high-precision measuring devices and other equipment systems, there is a demand for multi-channel temperature measurement. The temperature sensors are generally thermocouples and platinum resistors, which convert the temperature into weak electrical signals, which are then collected and converted by various onboard computers. However, for different equipment and applications, different specifications of platinum resistors and thermocouples will be selected, and their sensitivity and signal output range are not the same. The traditional circuit design needs to set different excitation methods and voltage gains according to the specifications of the temperature sensor. It lacks versatility and cannot meet the standardization and intelligent requirements of the new generation of aerospace equipment.

[0003] For temperature sensor measurement, the mainstream design scheme is to build a temperature sensor measurement front end through analog switches, instrumentation amplifiers and constant current sources or balanced bridges, and complete the measurement through a high-resolution ADC converter. As shown in Table 1 below, a comparison of the three mainstream temperature sensor measurement schemes is listed.

[0004] Table 1

[0005] The measurement schemes in the above table do not take into account the diversity of measurement methods for thermocouples and platinum resistors. The output of a thermocouple is a floating small voltage signal, the amplitude of which generally does not exceed 40mV. It is necessary to apply a voltage bias and provide a higher signal differential mode gain to ensure the accuracy of the measurement. The resistance of the platinum resistor changes with temperature. When measuring temperature, it needs to be excited by a constant current. When the current flows through the platinum resistor, a voltage is generated. The voltage amplitude is generally high and does not require a high voltage gain. The resistance value can be calculated by measuring the voltage and then converted to temperature. At the same time, platinum resistors generally have three types: PT100, PT800 and PT1000. The sensitivity differs by up to 10 times. The commonly used specifications of thermocouples are K-type, E-type, J-type, etc. Their sensitivity and voltage output range are also different. The specific design scheme needs to be determined based on the user's requirements for accuracy and cost.

[0006] The diversity of temperature sensors has resulted in the lack of a universal solution in the current market. Existing temperature measurement products only include single platinum resistance temperature testers or thermocouple temperature testers, and there is no full sensor solution. Summary of the invention

[0007] The invention provides a software-configurable multi-channel measurement circuit for universal platinum resistance and thermocouple, so as to solve the technical problems of low integration, low standardization and lack of universality of existing temperature sensor measurement solutions in the prior art.

[0008] In order to achieve the above object, the present invention adopts the following technical solution: A software-configurable multi-channel measurement circuit for universal platinum resistance and thermocouple, comprising an excitation output unit, a signal input unit and an information processing unit, wherein the excitation output unit comprises a voltage reference Vref buffer output circuit and a current reference Iref generating circuit, and the signal input unit is provided with a bias selection circuit and a signal conversion module; A voltage reference Vref buffer output circuit is used to provide a thermocouple bias voltage signal for a thermocouple channel; A current reference Iref generating circuit is used to provide an excitation current signal for a platinum resistance channel; A bias selection circuit is used to select access to a voltage reference Vref buffer output circuit or a current reference Iref generating circuit according to a GPIO control signal, and output a thermocouple bias voltage signal output by the voltage reference Vref buffer output circuit or an excitation current signal output by the current reference Iref generating circuit, thereby ensuring that the differential voltage signal at both ends of the thermocouple or the platinum resistance meets the requirements of the signal conversion module; A signal conversion module, used to amplify the voltage signal generated by the measurement channel and convert it into a digital signal; The information processing unit is used to output the GPIO control signal and output the temperature measurement data after processing the converted digital signal.

[0009] The excitation output unit also includes a precision voltage generating circuit, which is composed of a voltage reference chip, a filter capacitor C1 and a filter capacitor C2. The filter capacitor C1 and the filter capacitor C2 are connected in parallel, and the filter capacitor C1, the voltage reference chip and the filter capacitor C2 are connected in series. One end of the precision voltage generating circuit is connected in parallel with a voltage reference Vref and a current reference Iref, and the other end of the precision voltage generating circuit is connected in parallel with the power supply VCC and then grounded.

[0010] A voltage reference Vref buffer output circuit, the voltage reference Vref buffer output circuit is composed of an operational amplifier AMP2, resistors R3, R4 and capacitors C4, C5, the output end of the voltage reference Vref buffer output circuit is connected to the voltage reference Vref; one end of the resistor R3 is connected to the output end of the voltage reference chip, the other end of the resistor R3 is connected to the positive input end of the operational amplifier AMP2, the capacitor C4 is connected to one end of the resistor connected to the operational amplifier AMP2 and then grounded, the resistor R4 is connected to the output end of the operational amplifier AMP2, one end of the capacitor C5 is connected to the negative input end of the operational amplifier AMP2, the other end of the capacitor C5 is connected to the output end circuit of the operational amplifier AMP2 and is connected in series with the resistor R4.

[0011] In the voltage reference Vref buffer output circuit, the resistor R3 and the capacitor C4 form a low-pass filter, which is used to filter out the output noise of the precision voltage generating circuit.

[0012] The precision current reference Iref generating circuit is composed of an operational amplifier AMP1, a resistor R1, a resistor R2, a capacitor C3 and a multi-channel switch multiplexer MUX1. The negative electrode of the input end of the operational amplifier AMP1 is connected to the current reference Iref, one end of the resistor R2 is connected to the output end of the operational amplifier AMP1, and the other end is connected to the multiplexer MUX2; one end of the capacitor C3 is connected to the negative electrode of the input end of the operational amplifier AMP1, and the other end of the capacitor C3 is connected to the output end circuit of the operational amplifier AMP1, and is connected in series with the resistor R2 and then connected to the multiplexer MUX1, one end of the resistor R1 is connected to the negative electrode of the input end of the operational amplifier AMP1, and the other end of the resistor R1 is grounded.

[0013] The signal input unit also includes a surge protection circuit, which is connected to the input end of the bias selection circuit. The surge protection circuit is composed of a diode Z1, a diode Z2, a diode Z3 and a diode Z4, and is used to ensure that the interference voltage coupled by the thermocouple bias voltage signal output by the voltage reference Vref buffer output circuit or the excitation current signal output by the current reference Iref generation circuit through the long-line transmission process of the external sensor does not exceed the working range of the subsequent circuit.

[0014] The bias selection circuit is set as an analog switch S1, and the output end of the bias selection circuit is connected to a filter circuit, which is composed of a differential mode filter capacitor C1 and common mode filter capacitors C2 and C3 connected in series and a resistor R1 and a resistor R2 connected in parallel.

[0015] The signal input unit also includes a multi-way switch multiplexer MUX2, which is in differential form and is used to output differential voltage signals at both ends of thermocouples or platinum resistors in different measurement channels to the signal conversion module.

[0016] The signal conversion module includes a programmable gain amplifier PGA, the input end of the programmable gain amplifier PGA is connected to the output end of the multiplexer MUX2, the output end of the programmable gain amplifier PGA is connected to the AD converter, the programmable gain amplifier PGA amplifies the voltage signal with different voltage gains according to the type of the measured temperature sensor of the current channel, and the AD converter is used to convert the amplified voltage signal into a digital signal.

[0017] The information processing unit is composed of a step-down voltage regulator BUCK and a microcontroller MCU. The BUCK provides power for the information processing unit. The microcontroller MCU outputs GPIO control signals to the excitation output unit and the signal output unit according to the configuration information of different measurement channels.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The invention discloses a software-configurable multi-channel measurement circuit for universal platinum resistors and thermocouples. The integrated design greatly improves the integration of the measurement circuit, integrates multiple functional units and numerous components into one circuit, reduces the circuit board area and the number of components, and makes the entire circuit more compact. Compared with the traditional decentralized design, it not only saves space, but also reduces the problems such as signal interference that may be generated due to the complex connection between components, and improves the stability and reliability of the circuit. The workflow and interface of each unit and component are designed in accordance with standardization, and a unified measurement process and interface standard can be provided for platinum resistors of different specifications or various types of thermocouples. This improves the standardization of the measurement circuit, enhances the compatibility and scalability of the system, enables the measurement circuit to be easily integrated and docked with other devices, and improves the scope of use of the temperature measurement circuit of the invention. The excitation mode, bias mode and voltage gain coefficient of different channels can be flexibly configured by software to adapt to platinum resistors and thermocouples of different types and specifications. There is no need to customize a special measurement circuit for each sensor, which solves the problem that the existing measurement scheme lacks universality due to the diversity of temperature sensors, and realizes the universal measurement of multiple temperature sensors by a circuit. This greatly reduces design costs and complexity, improves production efficiency, and can widely meet the diverse needs of different users in the market for temperature sensor measurement.

[0019] Furthermore, the low-pass filter (composed of resistor R3 and capacitor C4) in the voltage reference Vref buffer output circuit effectively filters out noise, provides a stable bias voltage for thermocouple measurement, and reduces noise interference; the precision current reference Iref generation circuit ensures the stability of the output current and provides precise excitation current for platinum resistance measurement; the programmable gain amplifier accurately sets the gain according to the sensor type, and can amplify the weak sensor signal to a suitable range to facilitate high-precision conversion by the AD converter; the AD converter converts the analog signal into a digital signal to further improve the processing accuracy; the MCU calls the precise temperature conversion algorithm according to the sensor type (such as platinum resistance using the resistance-temperature characteristic formula, thermocouple based on the graduation table and interpolation algorithm), ensuring high-precision measurement from multiple links, and meeting the stringent requirements of high-precision measurement devices for temperature measurement accuracy.

[0020] Furthermore, the MCU in the information processing unit serves as the core control unit, and realizes intelligent management of the entire measurement process through software control. It can automatically switch measurement modes, adjust excitation and bias, control signal processing procedures, and perform data calculation and transmission according to different sensor types, without manual intervention in complex measurement parameter settings, greatly improving measurement efficiency and accuracy. At the same time, data interaction with external devices is realized through the UART interface, which facilitates system integration and remote monitoring, meets the requirements of intelligent measurement for the new generation of aerospace equipment, and improves the automation and intelligence level of the entire system.

[0021] Furthermore, the improvement of circuit integration reduces the circuit board area and the number of components, directly reducing the hardware cost. The low-power microcontroller MCU and reasonable circuit design (such as the optimized configuration of each unit component, the high efficiency of the signal processing process, etc.) reduce the overall power consumption. The precision voltage generation circuit provides a stable reference signal for other circuits to avoid repeated design of complex circuits, and the software configuration selects the appropriate working mode and parameters to reduce unnecessary energy consumption. This makes the measurement circuit have better economy and energy efficiency while ensuring high performance, improves the market competitiveness of the product, and is conducive to its wide promotion in cost-sensitive and power-demanding application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 : Schematic diagram of multi-channel measurement circuit module; Figure 2 : Schematic diagram of the multi-channel measurement circuit system architecture framework; Figure 3 : Schematic diagram of the excitation output unit circuit; Figure 4 : Schematic diagram of signal input unit circuit; Figure 5: Schematic diagram of the bias state of the analog switch of the signal input unit; Figure 6 : Flow chart of temperature measurement using multi-channel measurement circuit. DETAILED DESCRIPTION

[0023] 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.

[0024] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0025] like Figure 1 As shown, the multi-channel measurement circuit of the present invention includes an excitation output unit, a signal input unit and an information processing unit, the excitation output unit includes a voltage reference Vref buffer output circuit and a current reference Iref generating circuit, and the signal input unit is provided with a bias selection circuit and a signal conversion module; A voltage reference Vref buffer output circuit is used to provide a thermocouple bias voltage signal for a thermocouple channel; A current reference Iref generating circuit is used to provide an excitation current signal for a platinum resistance channel; A bias selection circuit is used to select access to a voltage reference Vref buffer output circuit or a current reference Iref generating circuit according to a GPIO control signal, and output a differential voltage signal across the thermocouple or platinum resistance based on a thermocouple bias voltage signal output by the voltage reference Vref buffer output circuit or an excitation current signal output by the current reference Iref generating circuit; A signal conversion module, used to amplify the voltage signal generated by the measurement channel and convert it into a digital signal; The information processing unit is used to output the GPIO control signal and output the temperature measurement data after processing the converted digital signal.

[0026] See also Figure 2 , Figure 3 , Figure 4 and Figure 5 ,The design of this system includes three functional units, namely the ,excitation output unit, the signal input unit and the information processing unit. ,The excitation output unit, the signal input unit and the information ,processing unit are integrated to realize a multi-channel universal temperature ,measurement circuit; The framework topology of the excitation output unit is as follows Figure 3As shown, the topology is composed of the following components: filter capacitor C1 and filter capacitor C2 are connected in parallel, filter capacitor C1, voltage reference chip and filter capacitor C2 are connected in series, the voltage reference chip and filter capacitor C1 and filter capacitor C2 together form a precision voltage generating circuit, one end of the precision voltage generating circuit is connected in parallel with a voltage reference Vref and a current reference Iref, the other end of the precision voltage generating circuit is connected in parallel with a power supply VCC and then grounded, and the precision voltage generating circuit provides corresponding reference signals for the voltage reference Vref and the current reference Iref; The operational amplifier AMP2, resistors R3, R4 and capacitors C4, C5 form a voltage reference Vref buffer output circuit, the output end of the voltage reference Vref buffer output circuit is connected to the voltage reference Vref; one end of the resistor R3 is connected to the output end of the voltage reference chip, the other end of the resistor R3 is connected to the positive input end of the operational amplifier AMP2, the capacitor C4 is connected to one end of the resistor connected to the operational amplifier AMP2 and then grounded, the resistor R3 and the capacitor C4 form a low-pass filter, further filtering out the output noise of the voltage reference chip; the resistor R4 is a current limiting resistor, the resistor R4 is connected to the output end of the operational amplifier AMP2, to prevent the Vref signal output by the amplifier AMP from being short-circuited externally and causing circuit failure; the capacitor C5 is a compensation capacitor, one end of the capacitor C5 is connected to the negative input end of the operational amplifier AMP2, the other end of the capacitor C5 is connected to the output end circuit of the operational amplifier AMP2, and is connected in series with the resistor R4, for improving the ability of the operational amplifier AMP2 to carry capacitive loads; Operational amplifier AMP1, resistor R1, resistor R2, capacitor C3 and multi-channel switch multiplexer MUX1 form a precise current reference Iref generation circuit. Operational amplifier AMP1 forms a feedback loop through resistor R2, multi-channel switch multiplexer, external measured platinum resistor and resistor R1. The negative electrode of the input end of operational amplifier AMP1 is connected to the current reference Iref to ensure that the current of all components in this loop is Iref; resistor R2 plays a role of current limiting. One end of resistor R2 is connected to the output end of operational amplifier AMP1, and the other end is connected to the multiplexer MUX2. Capacitor C3 is a compensation capacitor. One end of capacitor C3 is connected to the negative electrode of the input end of operational amplifier AMP1, and the other end of capacitor C3 is connected to the output end circuit of operational amplifier AMP1, and connected in series with resistor R2 and then connected to the multiplexer MUX1 to ensure the phase margin of the amplifier and the stability of the output current; one end of resistor R1 is connected to the negative electrode of the input end of operational amplifier AMP1, and the other end of resistor R1 is grounded. Multi-channel switch multiplexer MUX2 is responsible for outputting the current reference Iref to the corresponding platinum resistor channel.

[0027] The topology diagram of the signal input unit is as follows: Figure 4As shown in the figure, the topology consists of the following components: the signal input unit can include multiple input channels. Taking channel VIN0 as an example, the voltage regulator diodes or TVS diodes Z1, Z2, Z3, and Z4 form an input surge protection circuit to ensure that the input voltage signal is in the working range of the back-end device; the analog switch S1 is the bias input selection. When S1 is connected to the voltage reference Vref through the resistor R5, the current channel can be configured as a thermocouple channel to provide a bias for the floating voltage signal output by the thermocouple. When S1 is connected to the current reference Iref, the current channel can be configured as a platinum resistor channel to provide a current excitation signal for the platinum resistor. The control end of the analog switch S1 is controlled by the GPIO of the MCU; the resistors R1, R2, and the capacitors C1, C2, and C3 are EMI filtering circuit, where C1 is a differential mode filter capacitor, and C2 and C3 are common mode filter capacitors; the multiplexer MUX2 is in differential form, and the differential voltage signals at both ends of the measured temperature sensors of different channels are selected to be sent to the rear-end programmable gain amplifier for subsequent processing, and the control end of the multiplexer MUX2 is controlled by the GPIO of the MCU; the programmable gain amplifier PGA and the ADC converter are the back stage of the signal input unit, and the programmable gain amplifier PGA amplifies different voltage gains according to the type of the measured temperature sensor of the current channel, and sends it to the ADC converter for sampling. The amplification factor is controlled by the GPIO of the MCU, and the data interface and control port of the ADC converter are also connected to the corresponding peripherals of the MCU.

[0028] The information processing unit consists of a step-down regulated power supply BUCK and a low-power microcontroller MCU. The step-down regulated power supply BUCK provides power for the information processing unit. The microcontroller MCU controls the multiplexers and analog switches internally, receives the sampled data from the ADC converter, converts the sampled voltage data into temperature values, and transmits and receives data externally through the UART interface. When the multiplexer MUX1 of the excitation output unit and the analog switch of the signal input unit are connected to Iref, it is the platinum resistance measurement mode. At this time, the measurement equivalent circuit is as follows: Figure 5 As shown in (a), it is a standard Kelvin four-wire connection; when the multiplexer of the excitation output unit is invalid and the analog switch of the signal input unit is connected to Vref, it is the thermocouple measurement mode. At this time, the measurement equivalent circuit is as follows Figure 5 (b) shows a floating voltage measurement mode with voltage bias.

[0029] The software control flow chart of the microcontroller MCU is as follows Figure 6As shown, after the temperature measurement starts, the microcontroller MCU starts the temperature measurement in the order of the measurement channels. The microcontroller MCU controls the multiplexer MUX1 of the excitation output unit to switch to the corresponding measurement channel according to the temperature sensor type of the current measurement channel. If the measurement channel is configured as a thermocouple, the common mode signal of the multiplexer MUX1 of the excitation output unit is switched to the voltage reference Vref, and the excitation output unit provides an excitation current signal to the thermocouple, so that the two ends of the thermocouple output a corresponding voltage signal, and the multiplexer MUX2 in the signal input unit sends the voltage signal generated at both ends of the thermocouple to the programmable gain amplifier PGA, and the programmable gain amplifier PGA changes the voltage gain multiple to 32 according to the configuration information in the GPIO control signal; if the measurement channel is configured as a platinum resistor, the common mode signal of the multiplexer MUX1 of the excitation output unit is switched to the current reference Iref, and the excitation output unit provides an excitation current signal to the platinum resistor, so that the two ends of the platinum resistor output a corresponding voltage signal, and the multiplexer MUX2 in the signal input unit sends the voltage signal generated at both ends of the thermocouple to the programmable gain amplifier PGA, and the programmable gain amplifier PGA changes the voltage gain multiple to 32 according to the configuration information in the GPIO control signal; if the measurement channel is configured as a platinum resistor, the common mode signal of the multiplexer MUX1 of the excitation output unit is switched to the current reference Iref, and the excitation output unit provides an excitation current signal to the platinum resistor, so that the two ends of the platinum resistor output a corresponding voltage signal, and the multiplexer MUX2 in the signal input unit The multiplexer MUX2 sends the voltage signal generated at both ends of the thermocouple to the programmable gain amplifier PGA. The programmable gain amplifier PGA changes the voltage gain multiple according to the platinum resistor model configured for the current measurement channel. If the platinum resistor model is PT100 platinum resistor, the voltage gain multiple of the programmable gain amplifier PGA is 16, otherwise, the voltage gain multiple of the programmable gain amplifier PGA is 2; the voltage signal amplified by the programmable gain amplifier PGA with a corresponding multiple is sent to the ADC converter for sampling; after the ADC converter completes sampling of the current channel, it outputs a digital signal to the microcontroller MCU, and the microcontroller MCU performs voltage-temperature calculation conversion and sends the current temperature measurement data to the external device through the UART interface; after the ADC converter completes sampling of the current channel, it continues to perform the temperature measurement sampling process of the next measurement channel in the channel sequence until the ADC converter completes sampling of the voltage signals output by all measurement channels, and the microcontroller MCU sends the temperature data of all measurement channels to the external device, and the temperature measurement process ends.

[0030] This embodiment provides a software-configurable universal platinum resistance and thermocouple multi-channel measurement circuit, which can realize a 16-input channel temperature measurement device through a rigid-flex printed circuit board. Each channel can be configured into different types of thermocouples and platinum resistance types through software to adapt to various working environments. The maximum data update frequency is 50Hz, the measurement resolution is ±0.1℃, the circuit size is 30mm×26mm×7mm, and a 64Pin direct plug package is used. The specific implementation method is as follows: Start the temperature measurement device, the step-down voltage regulator BUCK provides power to the information processing unit, and starts the temperature measurement in channel order. The microcontroller MCU in the information processing unit establishes a communication link with the external device through the UART interface. The microcontroller MCU uses a low-power controller; according to actual application requirements, the staff configures the temperature sensor type connected to each channel as a thermocouple or platinum resistance through an external device for 16 channels. The external device sends the configuration information of the 16 channels to the microcontroller MCU through the UART interface. The microcontroller MCU sets the relevant components in the excitation output unit and the signal input unit according to the received configuration information.

[0031] The microcontroller MCU selects one of the 16 channels in sequence for temperature measurement. In this embodiment, channel VIN0 is taken as an example. According to the channel sensor type selected in configuration 1, the microcontroller MCU outputs corresponding GPIO control signals to the multiplexer MUX1 in the excitation output unit and the analog switch, multiplexer MUX2 and programmable gain amplifier PGA in the information input unit to set the excitation mode and bias mode of the corresponding platinum resistance or thermocouple.

[0032] The multiplexer MUX1 in the excitation output unit switches to the EXC0 channel corresponding to the channel VIN0 according to the received GPIO control signal. If the channel VIN0 is configured as a platinum resistor, the precision voltage generation circuit in the excitation output unit provides a stable voltage signal for the precision current reference Iref generation circuit of the current reference Iref. The voltage signal is processed by the precision current reference Iref generation circuit and then outputs the current reference Iref. The multi-channel switch multiplexer MUX1 is responsible for outputting the current reference Iref to both ends of the corresponding platinum resistor, which is the platinum resistor measurement mode. At this time, the measurement equivalent circuit is formed as follows: Figure 5The Kelvin four-wire connection shown in (a) provides a constant current excitation for the platinum resistor, so that a voltage signal related to the temperature of the channel VIN0 is generated at both ends of the platinum resistor. At the same time, the signal input unit adjusts its analog switch S1 bias selection to connect to Iref according to the configuration information in the GPIO control signal to ensure that it is not connected to the voltage reference Vref, and the excitation output unit does not provide a bias voltage to the signal input unit. The multiplexer MUX2 in the signal input unit sends the voltage signal generated at both ends of the platinum resistor to the programmable gain amplifier PGA for processing. The programmable gain amplifier PGA receives the GPIO control signal output by the microcontroller MCU. The programmable gain amplifier PGA changes the voltage gain multiple according to the configuration information in the GPIO control signal. If the platinum resistor model configured in the EXC0 channel is a PT100 platinum resistor, the programmable gain amplifier PGA changes the voltage gain to 16 times; otherwise, the programmable gain amplifier PGA changes the voltage gain to 2 times. The voltage signal amplified by the corresponding multiple of the programmable gain amplifier PGA is sent to the ADC converter for sampling. The ADC converter converts the voltage signal into a digital signal and transmits the digital signal to the microcontroller MCU. After receiving the digital signal output by the ADC converter, the microcontroller MCU calls the corresponding temperature conversion algorithm according to the sensor type configured for the current channel. For platinum resistors, the microcontroller MCU uses the known current excitation value and the sampled voltage value to calculate the current resistance value according to the resistance-temperature characteristic formula of the platinum resistor, and then further converts it into the corresponding temperature value and outputs the temperature data of the current channel. The microcontroller MCU further sends the temperature data to external devices through the UART interface.

[0033] If channel VIN0 is configured as a thermocouple, the precision voltage generation circuit in the excitation output unit provides a reference voltage signal for the buffer output circuit of the voltage reference Vref. The reference voltage signal is filtered by a low-pass filter formed by resistor R3 and capacitor C4 and then outputs a stable voltage signal. The voltage signal is finally processed by the buffer output circuit and outputs a stable voltage reference Vref to the signal input unit, providing an excitation current for the thermocouple channel so that the two ends of the thermocouple output a corresponding voltage signal. At the same time, the signal input unit adjusts its analog switch S1 bias selection according to the GPIO control signal to connect to Vref, which is the thermocouple measurement mode. At this time, the measurement equivalent circuit is as follows: Figure 5(b) shows a floating voltage measurement mode with voltage bias. The multiplexer MUX2 in the signal input unit sends the voltage signal generated at both ends of the thermocouple to the programmable gain amplifier PGA for processing. The programmable gain amplifier PGA receives the GPIO control signal output by the microcontroller MCU. The programmable gain amplifier PGA changes the voltage gain multiple to 32 according to the configuration information in the GPIO control signal. The voltage signal amplified by the programmable gain amplifier PGA is sent to the ADC converter for sampling. The ADC converter converts the voltage signal into a digital signal and transmits the digital signal to the microcontroller MCU. After receiving the digital signal output by the ADC converter, the microcontroller MCU calls the corresponding temperature conversion algorithm according to the sensor type configured for the current channel. For thermocouples, the MCU calculates the current temperature value through the interpolation algorithm based on the pre-stored thermocouple graduation table and the sampled voltage value (taking into account the influence of the bias voltage), and then outputs the corresponding temperature data of the current channel. The microcontroller MCU further sends the temperature data to the external device through the UART interface. By polling the analog switch and multiple multiplexers as above, multiple different external temperature sensor measurements can be achieved.

[0034] In addition, it should be understood that although this specification is described in accordance with the implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art. The above content is only to illustrate the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A software-configurable multi-channel measurement circuit for universal platinum resistance and thermocouple, characterized in that: It includes an excitation output unit, a signal input unit and an information processing unit. The excitation output unit includes a voltage reference Vref buffer output circuit and a current reference Iref generating circuit. The signal input unit is provided with a bias selection circuit and a signal conversion module. A voltage reference Vref buffer output circuit is used to provide a thermocouple bias voltage signal for a thermocouple channel; A current reference Iref generating circuit is used to provide an excitation current signal for a platinum resistance channel; A bias selection circuit is used to select access to a voltage reference Vref buffer output circuit or a current reference Iref generating circuit according to a GPIO control signal, and output a thermocouple bias voltage signal output by the voltage reference Vref buffer output circuit or an excitation current signal output by the current reference Iref generating circuit, thereby ensuring that the differential voltage signal at both ends of the thermocouple or the platinum resistance meets the requirements of the signal conversion module; A signal conversion module, used to amplify the voltage signal generated by the measurement channel and convert it into a digital signal; The information processing unit is used to output the GPIO control signal and output the temperature measurement data after processing the converted digital signal.

2. A software-configurable universal platinum resistance and thermocouple multi-channel measurement circuit according to claim 1, characterized in that: The excitation output unit also includes a precision voltage generating circuit, which is composed of a voltage reference chip, a filter capacitor C1 and a filter capacitor C2. The filter capacitor C1 and the filter capacitor C2 are connected in parallel, and the filter capacitor C1, the voltage reference chip and the filter capacitor C2 are connected in series. One end of the precision voltage generating circuit is connected in parallel with a voltage reference Vref and a current reference Iref, and the other end of the precision voltage generating circuit is connected in parallel with a power supply VCC and then grounded.

3. The software-configurable universal platinum resistance and thermocouple multi-channel measurement circuit according to claim 1, characterized in that: The voltage reference Vref buffer output circuit is composed of an operational amplifier AMP2, resistors R3, R4 and capacitors C4, C5. The output end of the voltage reference Vref buffer output circuit is connected to the voltage reference Vref; one end of the resistor R3 is connected to the output end of the voltage reference chip, and the other end of the resistor R3 is connected to the positive input end of the operational amplifier AMP2. The capacitor C4 is connected to one end of the resistor connected to the operational amplifier AMP2 and then grounded. The resistor R4 is connected to the output end of the operational amplifier AMP2, one end of the capacitor C5 is connected to the negative input end of the operational amplifier AMP2, and the other end of the capacitor C5 is connected to the output end circuit of the operational amplifier AMP2 and is connected in series with the resistor R4.

4. A software-configurable universal platinum resistance and thermocouple multi-channel measurement circuit according to claim 3, characterized in that: In the voltage reference Vref buffer output circuit, the resistor R3 and the capacitor C4 form a low-pass filter, and the low-pass filter is used to filter out the output noise of the precision voltage generating circuit.

5. The software-configurable multi-channel measurement circuit for universal platinum resistance and thermocouple according to claim 1, characterized in that: The precision current reference Iref generating circuit is composed of an operational amplifier AMP1, a resistor R1, a resistor R2, a capacitor C3 and a multi-channel switch multiplexer MUX1. The negative electrode of the input end of the operational amplifier AMP1 is connected to the current reference Iref, one end of the resistor R2 is connected to the output end of the operational amplifier AMP1, and the other end is connected to the multi-channel switch multiplexer MUX2; one end of the capacitor C3 is connected to the negative electrode of the input end of the operational amplifier AMP1, and the other end of the capacitor C3 is connected to the output end circuit of the operational amplifier AMP1, and is connected in series with the resistor R2 and then connected to the multi-channel switch multiplexer MUX1, one end of the resistor R1 is connected to the negative electrode of the input end of the operational amplifier AMP1, and the other end of the resistor R1 is grounded.

6. A software configurable universal platinum resistance and thermocouple multi-channel measurement circuit according to claim 1, characterized in that: The signal input unit also includes a surge protection circuit, which is connected to the input end of the bias selection circuit. The surge protection circuit is composed of a diode Z1, a diode Z2, a diode Z3 and a diode Z4, and is used to ensure that the interference voltage coupled by the thermocouple bias voltage signal output by the voltage reference Vref buffer output circuit or the excitation current signal output by the current reference Iref generation circuit through the long-line transmission process of the external sensor does not exceed the working range of the subsequent circuit.

7. A software configurable universal platinum resistance and thermocouple multi-channel measurement circuit according to claim 6, characterized in that: The bias selection circuit is configured as an analog switch S1, and the output end of the bias selection circuit is connected to a filter circuit, which is composed of a differential mode filter capacitor C1 and common mode filter capacitors C2 and C3 connected in series and resistors R1 and R2 connected in parallel.

8. The software-configurable universal platinum resistance and thermocouple multi-channel measurement circuit according to claim 1, characterized in that: The signal input unit also includes a multi-way switch multiplexer MUX2, which is in differential form and is used to output differential voltage signals at both ends of thermocouples or platinum resistors in different measurement channels to the signal conversion module.

9. A software-configurable universal platinum resistance and thermocouple multi-channel measurement circuit according to claim 8, characterized in that: The signal conversion module includes a programmable gain amplifier PGA, the input end of the programmable gain amplifier PGA is connected to the output end of the multiplexer MUX2, the output end of the programmable gain amplifier PGA is connected to the AD converter, the programmable gain amplifier PGA amplifies the voltage signal with different voltage gains according to the type of the measured temperature sensor of the current channel, and the AD converter is used to convert the amplified voltage signal into a digital signal.

10. The software-configurable universal platinum resistance and thermocouple multi-channel measurement circuit according to claim 1, characterized in that: The information processing unit is composed of a step-down voltage-stabilizing power supply BUCK and a microcontroller MCU. The BUCK provides power for the information processing unit, and the microcontroller MCU outputs GPIO control signals to the excitation output unit and the signal output unit according to the configuration information of different measurement channels.

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