Channel number variable thermocouple and thermistor measurement multiplexing circuit

Abstract

The utility model belongs to the industrial production process control thermocouple, thermistor temperature measurement application field relates to a kind of thermocouple and thermistor measurement multiplexing circuit with variable channel number.The utility model by the C line of existing circuit is extended to the differential signal input end of new channel, the channel number of thermocouple and thermistor measurement multiplexing circuit can be realized variable, 8 / 16 / 24 channel thermocouple and thermistor measurement multiplexing circuit are conveniently increased to 12 / 24 / 36 channel thermocouple and thermistor measurement multiplexing circuit.

Description

Technical Field

[0001] This utility model relates to the application of thermocouples and resistance temperature measurement in industrial production process control, and in particular to a thermocouple and resistance temperature measurement multiplexing circuit with variable channel number. Background Technology

[0002] Thermocouples and resistance temperature detectors (RTDs) are the two most commonly used contact-type temperature sensing elements in industrial process control. Due to their stable performance, wide temperature range, long-distance signal transmission, simple structure, and ease of use, they are widely used in temperature monitoring within industrial process control. To reduce the number of thermocouple and RTD sensor measuring devices used, each device employs a multi-channel signal measurement method. Furthermore, to reduce the number of spare parts required, the device utilizes a universal measurement method for both thermocouple and RTD sensor signals.

[0003] Figure 1 This is a general-purpose measurement circuit for 8-channel thermocouple and RTD sensor signals, mainly composed of U1 to U8, U... C1 ~U C4 U i The circuit consists of a dual-channel electronic switch, an analog-to-digital converter (ADC), and other units. The resistance temperature detector (RTD) measurement employs a three-wire dual constant current source method. The circuit operation is as follows: 1. Resistance temperature measurement: (1) U1, U i Dual-channel electronic switch closed, U C1 One switch from 1C to RGND is closed, U2~U8, U C2 ~U C4 Both electronic switches are open, and constant current source I1 flows through U. i One of the switches of U1 flows into the circuit from terminal A1, through the line resistor R. LA1 Resistance temperature detector (RTD) R t1 Line resistance R Lc1 It flows out to C1, and then through U C1 The 1C to RGND switch flows back to the reference ground through resistor R0.

[0004] (2) Constant current source I2 flows through U i The other switch of U1 flows in from terminal B1, through the line resistor R. LB1 Line resistance R Lc1 It flows out to C1, and then through U C1 The 1C to RGND switch flows back to the reference ground through resistor R0.

[0005] (3) According to U A1B1 =U A1 -U B1 =[R LA1*I1+R t1 *I1+(R LC1 +R0)*(I1+I2)]-[R LB1 *I2+(R LC1 +R0)*(I1+I2)];Since the two constant current sources are equal, i.e., I1=I2, the connecting wires use the same multi-core cable, i.e., R LA1 =R LB1 =R LC1 Therefore, U A1B1 =R t1 *I1.

[0006] (4) The differential voltage U across A1 and B1 A1B1 After being switched and shifted to terminals a and b by the dual-channel electronic switch U1, the voltage U ab =U A1B1 Voltage U ab The signal is amplified by the preamplifier AMP of the analog-to-digital converter (ADC) and then converted into a digital quantity for data processing by the processor of the measuring device to obtain the thermal resistance R. t1 Voltage measurement value V at both ends Rt1 V Rt1 =G*R t1 *I1(G is the gain of the ADC preamplifier).

[0007] (5) Dual-channel electronic switches U1~U7, U C1 ~U C3 Both are disconnected, U8, U i Dual-channel electronic switch closed, U C4 One switch from 8C to RGND is closed. This is related to the thermal resistor R of channel 1. t1 Similarly, the thermal resistance R of the 8th channel can be obtained through measurement. t8 Voltage measurement value V at both ends Rt8 =G*R t8 *I1.

[0008] 2. Thermocouple measurement: (1) When the U1 dual-circuit electronic switch is closed, U2~U8, U i U C1 ~U C4 Both electronic switches are off, E t1 The differential voltage U across thermocouples A1 and B1 A1B1 After being switched and shifted to terminals a and b by the dual-channel electronic switch U1, the voltage U ab = U A1B1 Voltage U ab The signal is amplified by the preamplifier AMP of the analog-to-digital converter (ADC) and then converted into a digital value for data processing by the processor of the measuring device to obtain the thermal resistance E.t1 Voltage measurement value V at both ends Et1 V Et1 =G*U ab =G*U A1B1 (G is the gain of the ADC preamplifier).

[0009] (2) Dual-channel electronic switches U1~U7, U i U C1 ~U C4 All are disconnected, the U8 dual-channel electronic switch is closed, and the thermocouple E of the first channel is connected. t1 Similarly, the thermocouple E of the 8th channel can be obtained through measurement. t8 Voltage measurement value V at both ends Et8 =G*U A8B8 .

[0010] In conclusion, Figure 1 The existing technology corresponding to this circuit uses a three-wire resistance temperature detector (RTD) measurement method. The C-wires C1 to C8 of the 8-channel RTD are not connected and are not shared; each C-wire has an independent switch. However, in industrial applications, thermocouple sensors typically have more measurement points than RTD sensors. For example, when a device has 8 channels and uses 8 RTD sensors, if 8-12 thermocouple sensors are used, a single 8-channel device cannot meet the requirements, necessitating a combination of two devices using 8-12 thermocouple sensors. Utility Model Content

[0011] The purpose of this invention is to solve the technical problems existing in the background art. To this end, a thermocouple and resistance temperature detector (RTD) measurement multiplexing circuit with variable number of channels is provided, which expands the C line into a differential signal input terminal of a new channel, thereby increasing the number of channels of the measurement circuit.

[0012] To achieve the above objectives, the technical solution adopted by this utility model is as follows: A thermocouple and resistance temperature detector (RTD) measurement multiplexing circuit with a variable number of channels includes a temperature detection circuit with multiple channels, wherein the temperature detection circuit includes a dual-channel electronic switch one, a dual-channel electronic switch two, a dual-channel electronic switch three, a dual-channel electronic switch four, and a dual-channel electronic switch five. The KA and KB terminals of the dual-channel electronic switch one are electrically connected to constant current source one and constant current source two, respectively, and the INP and INN terminals of the dual-channel electronic switch one are electrically connected to the INP and INN terminals of the dual-channel electronic switch two, respectively. A thermocouple or resistance temperature detector (RTD) is electrically connected between terminals A and B of the dual-channel electronic switch 2. Terminal B of dual-channel electronic switch two returns to the reference ground via a C line through dual-channel electronic switch three, dual-channel electronic switch four, and a resistor; Two temperature detection circuits in multiple channels share a single dual-channel electronic switch. Connect the two C-wires of the shared dual-circuit electronic switch three to a thermocouple or resistance temperature detector. The INP and INN terminals of dual-channel electronic switch one are electrically connected to the INP and INN terminals of dual-channel electronic switch five, respectively. The SP and SN terminals of dual-channel electronic switch five are electrically connected to the SP and SN terminals of the shared dual-channel electronic switch three, respectively, and return to the reference ground via dual-channel electronic switch four and a resistor.

[0013] The following is a further defined technical solution of this utility model: the INP and INN terminals of the dual-channel electronic switch are electrically connected to the two input terminals of the analog-to-digital converter (ADC), respectively.

[0014] The following is a further defined technical solution of this utility model: the INP and INN terminals of the dual-channel electronic switch five are electrically connected to the two input terminals of the analog-to-digital converter (ADC), respectively.

[0015] The following is a further defined technical solution of this utility model: a temperature detection circuit with 8 channels, each temperature detection circuit with 8 C-wires, each pair of C-wires serving as the differential signal input terminal of one channel of the temperature detection circuit, used to connect thermocouples or resistance temperature detectors, thereby forming a temperature detection circuit with up to 12 channels.

[0016] Compared with the prior art, the present invention has the following technical effects: This invention expands the C-line of the existing circuit into a differential signal input terminal for a new channel, thereby enabling the number of channels in the thermocouple and RTD measurement multiplexing circuit to be variable. It can easily increase the number of channels in the 8 / 16 / 24 channel thermocouple and RTD measurement multiplexing circuit to 12 / 24 / 36 channel thermocouple and RTD measurement multiplexing circuit.

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a diagram showing the connection relationships of existing measurement circuits; Figure 2 This is a connection diagram of the measurement multiplexing circuit of this utility model. Detailed Implementation

[0020] To make the above-mentioned objects, features, and advantages of this utility model more apparent and understandable, the specific embodiments of this utility model will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a full understanding of this utility model. However, this utility model can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this utility model. Therefore, this utility model is not limited to the specific embodiments disclosed below.

[0021] like Figure 2 As shown, a thermocouple and resistance temperature detector (RTD) measurement multiplexing circuit with a variable number of channels is provided, mainly consisting of U1 to U8, U... C1 ~U C4 U i U E U R The circuit consists of a dual-channel electronic switch, an analog-to-digital converter (ADC), and other units. The resistance temperature detector (RTD) measurement employs a three-wire dual constant current source method. The circuit operation is as follows: 1. Resistance temperature measurement: (1) U1, U i U R Dual-channel electronic switch closed, U C1 When one switch from 1C to SP is closed, U2~U8, U C2 ~U C4 U E Both electronic switches are open, and constant current source I1 flows through U. i One of the switches of U1 flows into the circuit from terminal A1, through the line resistor R. LA1 Resistance temperature detector (RTD) R t1 Line resistance R Lc1 It flows out to C1, and then through U C1 The switch from 1C to SP, U R The switch from SP to RGND flows back to the reference ground through resistor R0.

[0022] (2) Constant current source I2 flows through U i The other switch of U1 flows in from terminal B1, through the line resistor R. LB1 Line resistance R Lc1 It flows out to C1, and then through U C1 The switch from 1C to SP, U R The switch from SP to RGND flows back to the reference ground through resistor R0.

[0023] (3) According to U A1B1 =U A1 -U B1 =[R LA1 *I1+R t1 *I1+(RLC1 +R0)*(I1+I2)]-[R LB1 *I2+(R LC1 Since the two constant current sources are equal, i.e., I1=I2, the connecting wires use the same multi-core cable, i.e., R0)*(I1+I2)]. LA1 =R LB1 =R LC1 Therefore, U A1B1 =R t1 *I1.

[0024] (4) The differential voltage U across A1 and B1 A1B1 After being switched and shifted to terminals a and b by the dual-channel electronic switch U1, the voltage U ab =U A1B1 Voltage U ab The signal is amplified by the preamplifier AMP of the analog-to-digital converter (ADC) and then converted into a digital value for data processing by the processor of the measuring device to obtain the thermal resistance R. t1 Voltage measurement value V at both ends Rt1 V Rt1 =G*R t1 *I1(G is the gain of the ADC preamplifier).

[0025] (5) Dual-channel electronic switches U1~U7, U C1 ~U C3 U E Disconnect both, U8 and U i U R Dual-channel electronic switch closed, U C4 One switch from 8C to SN is closed. This is related to the thermal resistor R of channel 1. t1 Similarly, the thermal resistance R of the 8th channel can be obtained through measurement. t8 Voltage measurement value V at both ends Rt8 =G*R t8 *I1.

[0026] 2. Thermocouple measurement: (1) When the U1 dual-circuit electronic switch is closed, U2~U8, U i U C1 ~U C4 U E U R Both electronic switches are off, E t1 The differential voltage U across thermocouples A1 and B1 A1B1 After being switched and shifted to terminals a and b by the dual-channel electronic switch U1, the voltage U ab = U A1B1 Voltage U abThe signal is amplified by the preamplifier AMP of the analog-to-digital converter (ADC) and then converted into a digital value for data processing by the processor of the measuring device to obtain the thermal resistance E. t1 Voltage measurement value V at both ends Et1 V Et1 =G*U ab =G*U A1B1 (G is the gain of the ADC preamplifier).

[0027] (2) Dual-channel electronic switches U1~U7, U i U C1 ~U C4 U E U R All are disconnected, the U8 dual-channel electronic switch is closed, and the thermocouple E of the first channel is connected. t1 Similarly, the thermocouple E of the 8th channel can be obtained through measurement. t8 Voltage measurement value V at both ends Et8 =G*U A8B8 .

[0028] (3) The eight C-wires C1 to C8 of the thermal resistor are converted into four pairs of differential signals C1 and C2 (E t9 C3 and C4 (E) t10 C5 and C6 (E) t11 C7 and C8 (E) t12 Input terminal.

[0029] Dual-channel electronic switches U1~U8, U i U C2 ~U C4 U R All disconnected, U C1 U E Both electronic switches are closed, E t9 The differential voltage U across thermocouples C1 and C2 C1C2 via dual-channel electronic switch U C1 U E Switching to terminals a and b, voltage U ab = U C1C2 Voltage U ab The signal is amplified by the preamplifier AMP of the analog-to-digital converter (ADC) and then converted into a digital value for data processing by the processor of the measuring device to obtain the thermocouple E. t9 Voltage measurement value V at both ends Et9 V Et9 =G*U ab =G*U C1C2 (G is the gain of the ADC preamplifier).

[0030] Dual-channel electronic switches U1~U8, Ui U C1 ~U C3 U R All disconnected, U C4 U E Both electronic switches are closed, E t12 The differential voltage U across thermocouples C7 and C8 C7C8 via dual-channel electronic switch U C4 U E Switching to terminals a and b, voltage U ab = U C7C8 Voltage U ab The signal is amplified by the preamplifier AMP of the analog-to-digital converter (ADC) and then converted into a digital value for data processing by the processor of the measuring device to obtain the thermocouple E. t12 Voltage measurement value V at both ends Et12 V Et12 =G*U ab =G*U C7C8 (G is the gain of the ADC preamplifier).

[0031] Therefore, the 8-channel temperature detection circuit became a 12-channel circuit. The entire circuit only added 2 dual-channel electronic switches, while the number of channels increased by 4.

[0032] Depend on Figure 2 This invention implements a thermocouple and resistance temperature detector (RTD) measurement multiplexing circuit with variable channel count. 8 channels can be converted into 12 channels, 16 channels into 24 channels, and 24 channels into 36 channels, thereby greatly reducing the number of industrial thermocouple sensor signal measurement devices required.

[0033] The above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model in any way. Any person skilled in the art can make many possible variations and modifications to the technical solution of this utility model using the disclosed methods and techniques, or modify it into equivalent embodiments with equivalent changes, without departing from the scope of the technical solution of this utility model. Therefore, all equivalent changes made based on the shape, structure, and principle of this utility model without departing from its technical solution should be covered within the protection scope of this utility model.

Claims

1. A multiplexed circuit for thermocouple and resistance temperature measurement with variable channel number, characterized in that, The temperature detection circuit includes multiple channels, and the temperature detection circuit includes dual-channel electronic switch one, dual-channel electronic switch two, dual-channel electronic switch three, dual-channel electronic switch four and dual-channel electronic switch five; The KA and KB terminals of the dual-channel electronic switch one are electrically connected to constant current source one and constant current source two, respectively, and the INP and INN terminals of the dual-channel electronic switch one are electrically connected to the INP and INN terminals of the dual-channel electronic switch two, respectively. A thermocouple or resistance temperature detector (RTD) is electrically connected between terminals A and B of the dual-channel electronic switch 2. Terminal B of dual-channel electronic switch two returns to the reference ground via a C line through dual-channel electronic switch three, dual-channel electronic switch four, and a resistor; Two temperature detection circuits in multiple channels share a single dual-channel electronic switch. Connect the two C-wires of the shared dual-circuit electronic switch three to a thermocouple or resistance temperature detector. The INP and INN terminals of dual-channel electronic switch one are electrically connected to the INP and INN terminals of dual-channel electronic switch five, respectively. The SP and SN terminals of dual-channel electronic switch five are electrically connected to the SP and SN terminals of the shared dual-channel electronic switch three, respectively, and return to the reference ground via dual-channel electronic switch four and a resistor.

2. The variable-channel thermocouple and resistance temperature detector (RTD) measurement multiplexing circuit as described in claim 1, characterized in that, The INP and INN terminals of the dual-channel electronic switch are electrically connected to the two input terminals of the analog-to-digital converter (ADC), respectively.

3. The variable-channel thermocouple and resistance temperature detector (RTD) measurement multiplexing circuit as described in claim 1, characterized in that, The INP and INN terminals of the dual-channel electronic switch are electrically connected to the two input terminals of the analog-to-digital converter (ADC), respectively.

4. The variable-channel thermocouple and resistance temperature detector (RTD) measurement multiplexing circuit as described in claim 1, characterized in that, A temperature detection circuit with 8 channels has 8 C-lines. Each pair of C-lines serves as the differential signal input terminal for one channel of the temperature detection circuit, which is used to connect to a thermocouple or resistance temperature detector, thereby forming a temperature detection circuit with up to 12 channels.

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