A temperature measurement module circuit for universal resistance type temperature sensor input

Abstract

The utility model discloses a general resistance type temperature sensor input's temperature measurement module circuit, including resistance type input interface circuit, constant current source to interface circuit output constant current, the voltage value of temperature value representation is generated at its two ends, and the same phase input end connection of connection in differential amplifier, and the reference power is selected and switches over by change -over switch S1, and is connected to the inverting input end of differential amplifier, and the amplification factor of differential amplifier is converted into different amplification factor by change -over switch S2 and S3 synchronous, and change -over switch S1, S2 and S3 are a group of synchronous change -over switch. Differential amplifier subtracts reference voltage and then amplifies temperature voltage value according to the amplification factor. The circuit of the utility model is suitable for the unified access conditioning of PT100, PT1000 or NTC 50k and other various resistance type temperature sensors through three or more synchronous switch switching technology, and has the advantages of easy temperature measurement starting point and temperature measurement endpoint implementation.

Description

Technical Field

[0001] This utility model belongs to the field of temperature measurement technology, specifically relating to a temperature measurement module circuit with input of a general-purpose resistance temperature sensor. Background Technology

[0002] In intelligent building monitoring and control applications, DDC input terminals typically have multiple input types such as 0-5V, 0-10V, 0-20mA, and 4-20mA, with some input channels for resistance-type temperature sensors. Most of these are "two-wire" input methods, which not only limits the direct application of resistance-type temperature sensors but also severely weakens the measurement accuracy of precision temperature measurement using resistance-type temperature sensors, primarily represented by PT100.

[0003] Even for resistive temperature sensor input channels, specific types are strictly limited. In particular, with "two-wire" temperature measurement, the actual temperature value sampled by the DDC is generally too high due to the influence of the connection line resistance, leading to a deviation from the target temperature value for control.

[0004] Furthermore, for resistance-type temperature transmitters, the temperature measurement range is typically the "full range" of the corresponding sensor. For example, the PT100 platinum resistance temperature transmitter has a measurement range of -200℃ to +850℃. This significantly reduces the "absolute accuracy" compared to the specific temperature measurement range (-20℃ to +50℃) required for intelligent building monitoring and control. Occasionally, segmented resistance-type temperature transmitters are available, but these are sold as a fixed, complete unit within the resistance-type temperature sensor category.

[0005] In fact, in centralized central air conditioning intelligent control (DDC) systems in the building industry, the cold and hot circuit pipes and sensors are customized and installed by the contractor. In order to reduce costs, resistance-type temperature sensors (body) are often used, such as PT100, PT1000, or NTC 50k, etc. This causes significant trouble when third parties install DDC systems, such as "the two types do not match".

[0006] The specific issue of adapting resistive temperature sensors to the "uncertain type" of engineering sites, while still requiring DDC to install them within a specified period and achieve high-precision temperature sampling, is of great practical significance. Utility Model Content

[0007] To address the aforementioned problems in the existing technology, this utility model provides a temperature measurement module circuit with input from a universal resistance-type temperature sensor.

[0008] To achieve the above objectives, this utility model provides the following technical solution:

[0009] A general-purpose temperature measurement module circuit for a resistive temperature sensor input includes a resistive input interface circuit AB. A constant current source I1 outputs a constant current to the interface circuit, generating a voltage value representing the temperature value at its two terminals. This voltage value is connected to the non-inverting input (+) of a differential amplifier. A reference power supply E1 or E2 is selected and switched by a changeover switch S1 and connected to the inverting input (-) of the differential amplifier. The amplification factor of the differential amplifier is synchronously converted to different amplification factors by changeover switches S2 and S3. Changeover switches S1, S2, and S3 form a set of synchronous changeover switches.

[0010] Furthermore, the input interface circuit is applicable to resistance-type temperature sensors such as PT100, PT1000 and NTC 50k, which are excited by a constant current source I1, generating a voltage value representing the temperature value at their two ends, which is connected to the non-inverting input of the differential amplifier.

[0011] Furthermore, the reference power supply E1 or E2 is connected to the inverting input of the differential amplifier to "subtract" the voltage value corresponding to the temperature measurement start point of the corresponding sensor. It includes a reference power supply with multiple loops, and the specific value of the reference voltage determines the lower limit value (temperature measurement start point) of the temperature measurement of the corresponding temperature sensor.

[0012] Furthermore, the differential amplifier circuit consists of a precision operational amplifier, preamplifier resistors R1 and R3, and feedback resistors R21 / R22 and R41 / R42, etc. The amplification factor is synchronously converted by S2 and S3 to produce different amplification factors. It includes an extended circuit form with preamplifier resistors, multiple feedback resistors, and multiple groups of switching switches. The amplification factor of the amplifier determines the upper limit of the corresponding sensor temperature measurement (temperature measurement termination point).

[0013] Furthermore, the changeover switches S1, S2, and S3 include mechanical changeover switches and electronic switches.

[0014] Compared with the prior art, the beneficial effects of this utility model are as follows: This utility model, through a very simple electronic circuit design, sets a selection switch to correspond to the input of different types of resistive temperature sensors, and uniformly converts them into voltage value output corresponding to a certain temperature range, which is directly connected to the voltage type port of the DDC. It has many advantages such as simple circuit structure, high conversion accuracy, low cost, and intuitive and obvious type selection. Attached Figure Description

[0015] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0016] Figure 1 This is a circuit diagram of a temperature measurement module for a general-purpose resistive temperature sensor input according to this utility model.

[0017] Figure 2This is an example diagram of a temperature measurement module circuit with input from a general-purpose resistive temperature sensor. Detailed Implementation

[0018] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the present invention, and therefore only show the components relevant to the present invention.

[0019] The modular circuit of this invention employs a set of selector switches to select a specific resistive temperature sensor. The sensor is excited by a constant current source, generating a voltage value representing the temperature, which is connected to the non-inverting input of a differential amplifier. Simultaneously, the selector switches select the voltage value of a reference power supply, connected to the inverting input of the differential amplifier. The selector switches also simultaneously select the values ​​of the amplifying resistors within the differential amplifier to achieve different amplification factors. By setting the voltage value at the inverting input of the differential amplifier, the lower limit (temperature measurement start point) of the temperature measurement for a certain type of resistive sensor is determined. By changing the amplification factor of the differential amplifier, the upper limit (temperature measurement end point) of the temperature measurement for a certain type of resistive sensor is determined. The selector switches can be mechanical, such as a multi-band switch, or electronic, such as a CD4053.

[0020] like Figure 1 As shown,

[0021] The two input contacts, A and B, are connected "locally" to a resistive temperature sensor. A constant current source excites the resistive temperature sensor, causing it to generate a voltage value corresponding to the measured temperature. This voltage value is connected to the non-inverting input (+) of a differential amplifier. The reference power supply E1 or E2 is determined by the position of the selector switch S1. Resistors R1, R21 or R22, R3, R31 or R32, and operational amplifier U2 form a "differential amplifier." The position of R21 or R22 is determined by the position of the selector switch S2, and the position of R31 or R32 is determined by the position of the selector switch S3. The selector switches S1, S2, and S3 are a set of multi-chip synchronously switching position switches or selection switches. When a certain type of resistive temperature sensor is confirmed, the synchronous selector switch rotates to the corresponding position. At this time, corresponding to a specific measured temperature range, combined with the predetermined amplification factor of the differential amplifier, a 0-5V or 0-10V voltage signal is output.

[0022] like Figure 2 As shown,

[0023] According to the ITS-90 standard, the operating current of the platinum resistance temperature sensor is 100uA. The constant current source I1 can be a high-precision constant current source composed of "back-to-back" dual transistors, or a higher-precision constant current device such as REF200AU, to provide the operating current to the AB terminals. For simplicity, this explanation will only take the PT100 platinum resistance as an example and use the commonly used measurement and control range of -20℃ to +50℃ in building intelligence as the calculation parameters.

[0024] U1 uses a TL431 or similar high-precision voltage regulator chip, or a REF series higher-precision voltage reference source chip to output a 2.5V reference voltage. The reference voltage Ver1 is generated by voltage division through RJ1 and RJ2, and the reference voltage Ver2 is generated by voltage division through RJ3 and RJ4. More reference voltages Vern can be used to accommodate a wider range of resistive temperature sensor inputs.

[0025] The resistance of the PT100 platinum resistance thermometer is 92.160Ω at -20℃ and 119.395Ω at +50℃. Under a 100µA excitation, the voltage generated at the starting point of the temperature measurement range (-20℃) is 9.216mV; the voltage at the ending point of the temperature measurement range (50℃) is 11.939mV.

[0026] Assume the output voltage corresponding to this temperature measurement range is 0-5V, and assume that electronic switch U3 is selected by default at Y1A. Take resistors RJ1 (and RJ2) as 1kΩ. Then, when the value of resistor RJ2 is 3.7Ω, Ver1 is 9.216mV. This voltage value is subtracted from the "initial value" of the differential amplifier (-).

[0027] With the differential amplifier's preamplifier resistors R1 and R3 set to 1kΩ, the ΔV (11.939mV - 9.216mV = 2.723mV) is amplified to 5V. The corresponding resistors R21 and R4 can be calculated to be 1835kΩ.

[0028] Assuming the construction site uses a PT1000 platinum resistance temperature sensor, the resistance value is 921.599Ω at -20℃ and 1193.971Ω at +50℃. The corresponding RJ4 is 38.27Ω, and resistors R22 and R42 are 183.6kΩ.

[0029] U3 is a CD4053 type "three-channel 2-to-1" analog gating switch. When the selected terminals SA, SB, and SC are connected to a low level, their respective output terminals ZA, ZB, and ZC are connected to their respective first input terminals Y0A, Y0B, and Y0C; otherwise, they are connected to their respective second input terminals Y1A, Y1B, and Y1C. In the example above, when PT100 is connected, DIP switch S4 is in the off state; when PT1000 is connected, S4 is grounded.

[0030] This section uses an ideal operational amplifier as an example to illustrate the principle of this novel application. In practical applications, to further improve accuracy, "followers" can be inserted at the reference power supply output terminal (Vern) and the sensor signal output terminal to perform impedance transformation. The differential amplifier first amplifies the signal by a smaller factor before performing further (secondary) amplification.

[0031] Similarly, for resistive temperature sensor inputs such as NTC10k, NTC50k, and NTC100k, setting more reference voltage values, more amplifying resistors, and more (electronic selection) switches can realize the input conversion of more types of resistive temperature sensors, which is very convenient for the need to convert resistance (temperature) to voltage values.

[0032] For the sake of "simplicity", details such as the operational amplifier power supply circuit have been omitted in the above illustrative examples.

[0033] Typically, the resolution of the 0-5V input channel of a DDC is 1mV. Platinum resistance thermometers exhibit a basically linear temperature measurement pattern in localized areas. Based on the calculation example above, the conversion accuracy of this temperature measurement module is close to 0.014℃, which fully meets the requirements for "high-precision" temperature measurement.

[0034] Furthermore, in the above calculation example, the initial and final temperature measurement points and the corresponding voltage output values ​​can be determined by designing the values ​​of the appropriate resistors, either as 0-10V output or by adding additional circuitry to convert it to 4-20mA, etc.

[0035] Furthermore, if a 3-piece / group "9-to-1" rotary DIP switch is used, it can accommodate the input of 9 different types of resistance temperature sensors.

[0036] Furthermore, if the temperature measurement module uses a rotary DIP switch, it has a clear position indicator; if it uses a multi-channel electronic switch, different input types can be achieved through "DIP switch combinations".

[0037] In summary, this utility model discloses a universal temperature measurement module circuit for resistive temperature sensor input, including a resistive temperature sensor access circuit, an amplification circuit with a differential amplifier as the main body, the amplification factor of which is controlled by changeover switches S2 and S3, and the inverting input terminal of the amplification circuit connected to a reference power supply E1 or E2, which is switched synchronously by changeover switch S1 and S2 and S3. A constant current source I1 provides operating current to the resistive temperature sensor, generating a voltage value representing the temperature value across its terminals, which is connected to the non-inverting input terminal of the differential amplifier. The differential amplifier subtracts the reference voltage and amplifies the temperature voltage value by a predetermined amplification factor. This utility model's circuit, through three or more synchronous switching technology, is suitable for unified access and conditioning of various resistive temperature sensors such as PT100, PT1000, or NTC 50k, and has significant advantages such as easy implementation of the temperature measurement start and end points.

[0038] The above embodiments are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, these obvious variations or modifications derived from the spirit of the present invention are still within the protection scope of the present invention.

Claims

1. A temperature measurement module circuit for a general-purpose resistance-type temperature sensor input, characterized in that: The circuit includes a resistive input interface circuit AB, a constant current source I1 that outputs a constant current to the interface circuit, generating a voltage value representing the temperature value at its two ends, which is connected to the non-inverting input of the differential amplifier; a reference power supply E1 or E2 is selected and switched by a changeover switch S1 and connected to the inverting input of the differential amplifier; the amplification factor of the differential amplifier is synchronously converted to different amplification factors by changeover switches S2 and S3; changeover switches S1, S2 and S3 are a set of synchronous changeover switches.

2. The temperature measurement module circuit for a general-purpose resistance-type temperature sensor input as described in claim 1, characterized in that: The input interface circuit is suitable for resistance-type temperature sensors, which are excited by a constant current source I1, generating a voltage value representing the temperature value at their two ends, which is connected to the non-inverting input of a differential amplifier.

3. The temperature measurement module circuit for a general-purpose resistance-type temperature sensor input as described in claim 2, characterized in that: The types of resistance-type temperature sensors include PT100, PT1000, and NTC 50k.

4. The temperature measurement module circuit for a general-purpose resistance-type temperature sensor input as described in claim 1, characterized in that: The reference power supply E1 or E2 is used to "subtract" the voltage value corresponding to the starting point of the temperature measurement of the corresponding sensor. It is connected to the inverting input terminal of the differential amplifier. The temperature measurement module circuit includes multiple reference power supplies. The specific value of the reference voltage of the reference power supply determines the lower limit value of the temperature measurement of the corresponding temperature sensor.

5. The temperature measurement module circuit for a general-purpose resistance-type temperature sensor input as described in claim 1, characterized in that: The amplifier circuit, which is mainly based on a differential amplifier, includes a precision operational amplifier, preamplifier resistors R1 and R3, and feedback resistors R21 / R22 and R41 / R42. The amplification factor is synchronously converted from different amplification factors by S2 and S3. The temperature measurement module circuit includes an extended circuit form with a preamplifier, multiple feedback resistors, and multiple groups of switching switches. The amplification factor of the amplifier determines the upper limit of the temperature measurement of the corresponding sensor.

6. The temperature measurement module circuit for a general-purpose resistance-type temperature sensor input as described in claim 1, characterized in that: The changeover switches S1, S2 and S3 include mechanical changeover switches and electronic switches.

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