PT100-based narrow-range temperature measurement circuit

Abstract

The utility model relates to the technical field of temperature measuring circuits, in particular to a PT100-based narrow-range temperature measuring circuit, which comprises a voltage stabilizing module, a Wheatstone bridge module and a differential amplification circuit module. The voltage stabilizing module comprises a voltage stabilizing source, and a voltage stabilizing resistor R2 and a voltage stabilizing resistor R3 which are arranged in parallel with the voltage stabilizing source; the Wheatstone bridge module comprises a bridge resistor R4, a bridge resistor R5, a bridge resistor R6 and a bridge resistor R0 which are sequentially arranged on four bridge arms, and the resistance value of the resistor R0 is PT100; the differential amplification circuit module comprises an operational amplifier, a matching resistor R7, a matching resistor R8, a matching resistor R9 and a matching resistor R10. Based on the circuit design, the application can be ensured to meet the use requirement in a normal temperature range, and meanwhile, as the temperature range is compressed, the measurement precision is improved, and as long as the device selection precision meets the requirement, the temperature measurement precision can be ensured. Meanwhile, due to the fact that the circuit is simple, the circuit has the huge advantages of high stability, high reliability and low cost.

Description

TECHNICAL FIELD

[0001] The utility model relates to temperature measurement circuit technical field especially relates to a narrow range temperature measurement circuit based on PT100. BACKGROUND

[0002] Temperature measurement has important application value in various fields, including automotive electronics, consumer electronics, industrial equipment, smart home, industrial automation and medical devices.

[0003] The temperature measurement method of PT100 mainly has the following several kinds:

[0004] Bridge method: two-wire and three-wire connection mode usually adopts bridge method measurement. By measuring the voltage signal output by the bridge, the resistance value of PT100 can be calculated, and then the temperature value can be obtained according to the corresponding relationship between resistance and temperature.

[0005] Direct measurement method: four-wire connection mode usually adopts direct measurement method. By constant current source sending current, and measuring the voltage value of PT100 both ends, according to Ohm's law, the resistance value of PT100 is calculated, and then the temperature value is obtained according to the corresponding relationship between resistance and temperature.

[0006] PWM measurement method: by designing circuit to let output frequency and resistance value be proportional relationship (F=KR), wherein F is frequency, K is constant, R is resistance value. By measuring frequency, the resistance value of PT100 can be indirectly obtained, and then the temperature is finally measured according to the relationship between resistance value and temperature. This method has lower requirement for single chip microcomputer, only needs to have timer and interrupt function.

[0007] Although the above three methods can realize temperature measurement, the measurement accuracy of direct measurement method depends on stable constant current source, and the accuracy of power supply has great influence on measurement accuracy. High-precision constant current source is also high in price. Although PWM measurement method has low requirement for devices, it needs to use high-level single chip microcomputer to generate PWM waveform, and the number of PWM channels generated by single chip microcomputer is limited, so multiple single chip microcomputers are needed in multi-channel temperature collection, resulting in high cost and difficulty in batch production. Therefore, most of the existing technology still adopts bridge method measurement. In order to adapt to most application scenarios, the temperature range is as high as several hundred degrees, and some even reach thousands of degrees, so it is difficult to balance the temperature range, accuracy, response speed and stability to a certain extent. Therefore, the utility model develops a narrow range temperature measurement circuit based on PT100 to solve the problems existing in the prior art. Utility model content

[0008] The utility model aims at: provide a kind of narrow-range temperature measurement circuit based on PT100, to solve the problem of poor temperature measurement accuracy and stability of PT100 in prior art.

[0009] The utility model technical scheme is: a kind of narrow-range temperature measurement circuit based on PT100, including input and output, voltage stabilizing module, Wheatstone bridge module and differential amplifier circuit module being set between input and output;

[0010] The voltage stabilizing module includes a voltage source, voltage stabilizing resistor R2 and voltage stabilizing resistor R3 connected in parallel with the voltage source;

[0011] The Wheatstone bridge module includes bridge resistor R4, bridge resistor R5, bridge resistor R6 and bridge resistor R0 arranged in sequence on four bridge arms, and the bridge resistor R0 is the resistance value of PT100;Bridge resistor R4 is equal to bridge resistor R5;

[0012] The differential amplifier circuit module includes an operational amplifier, matching resistor R7, matching resistor R8, matching resistor R9 and matching resistor R10;The positive input of the operational amplifier is connected between the bridge resistor R4 and the bridge resistor R0, and the negative input of the operational amplifier is connected between the bridge resistor R5 and the bridge resistor R6;Matching resistor R7 is equal to matching resistor R8, and matching resistor R9 is equal to matching resistor R10.

[0013] Preferably, in the voltage stabilizing module, the voltage source uses TL431, and in combination with voltage stabilizing resistor R2 and voltage stabilizing resistor R3, a stable reference voltage is output.

[0014] Preferably, the voltage stabilizing module further includes a capacitor C3 connected in parallel.

[0015] Preferably, in the differential amplifier circuit module, the operational amplifier uses TLV2333, the signal amplification multiple is set to 40 times, and the operational amplifier is powered by single 5V.

[0016] Preferably, a filter module and a voltage divider module are further provided between the input and the voltage stabilizing module.

[0017] Preferably, the filter module includes a capacitor C1 and a capacitor C2;The capacitor C1 and the capacitor C2 are connected in parallel between the input and the ground terminal respectively.

[0018] The voltage divider module includes a resistor R1 connected in series in the circuit.

[0019] Preferably, the output end is further connected with an AD conversion module.

[0020] Preferably, the differential amplification circuit module is based on rail-to-rail operational amplifier, the output voltage is 5V, and the temperature range is -46 DEG C to 86 DEG C.

[0021] Compared with the prior art, the utility model has the advantages of:

[0022] The application is based on circuit design, can guarantee that the use in normal temperature range is met, improves the measurement precision because the temperature range is compressed, and the temperature measurement precision can be guaranteed as long as the device selection precision reaches the requirement. BRIEF DESCRIPTION OF DRAWINGS

[0023] The utility model will be further described in connection with the drawings and embodiments:

[0024] Figure 1 A narrow-range temperature measurement circuit structure based on PT100;

[0025] Figure 2 A circuit structure of the voltage stabilizing module;

[0026] Figure 3 A circuit structure of the Wheatstone bridge module;

[0027] Figure 4 A circuit structure of the differential amplification circuit module.

[0028] Wherein: 1, input end, 2, output end, 3, ground end, 4, filter module, 5, voltage division module, 6, voltage stabilizing module, 61, voltage stabilizing source, 7, Wheatstone bridge module, 8, differential amplification circuit module, 81, operational amplifier. DETAILED DESCRIPTION

[0029] The content of the utility model will be further described in connection with specific embodiments:

[0030] As Figure 1 shown, a narrow-range temperature measurement circuit based on PT100, comprising input end and output end, filter module, voltage division module, voltage stabilizing module, Wheatstone bridge module and differential amplification circuit module are arranged between the input end and the output end.

[0031] The filter module is arranged between the input end and the voltage stabilizing module, and the filter module comprises capacitor C1 and capacitor C2; capacitor C1 and capacitor C2 are respectively connected in parallel between the input end and the ground end, wherein the capacitance values of capacitor C1 and capacitor C2 are respectively set as 1 μF and 100 nF.

[0032] The voltage dividing module includes a resistor R1 connected in series in the circuit, and in the embodiment, the resistance of the resistor R1 is set to 300Ω, and a certain proportion of voltage is distributed by being connected in series in the circuit to provide a required specific voltage for other elements in the circuit.

[0033] In combination Figure 2 As shown, the voltage stabilizing module includes a voltage stabilizing source, a voltage stabilizing resistor R2 and a voltage stabilizing resistor R3 connected in parallel with the voltage stabilizing source; the voltage stabilizing source is a TL431, which is a controllable precision voltage stabilizing source, and the output voltage can be set to any value in the range from 2.5V to 36V by using two resistors. In the embodiment, the voltage stabilizing source TL431 is combined with the voltage stabilizing resistor R2 and the voltage stabilizing resistor R3, the resistance of the voltage stabilizing resistor R2 is set to 200Ω, and the resistance of the voltage stabilizing resistor R3 is set to 1kΩ, to output a stable 3V reference voltage.

[0034] The voltage stabilizing module further includes a capacitor C3 connected in parallel, and in the embodiment, the capacitance of the capacitor C3 is set to 100nF, and the capacitor C3 reduces output voltage fluctuation, improves system stability, filters high-frequency noise and protects circuit elements.

[0035] In combination Figure 3 As shown, the Wheatstone bridge module includes a bridge resistor R4, a bridge resistor R5, a bridge resistor R6 and a bridge resistor R0 connected in sequence on four bridge arms, and the bridge resistor R0 is a resistance value of a PT100; the bridge resistor R4 is equal to the bridge resistor R5. In the embodiment, the resistances of the bridge resistor R4 and the bridge resistor R5 are set to 1kΩ, the resistance of the bridge resistor R6 is set to 82Ω, and the resistance of the bridge resistor R0 ranges from 82Ω to 137Ω.

[0036] In the application, R4, R5, R6 and R0 (PT100) are used to constitute a measurement bridge, and when the resistance of R0 (PT100) and the resistance of R6 are not equal, the measurement bridge outputs a differential pressure signal of an mV level.

[0037] In combination Figure 4 As shown, the differential amplification circuit module includes an operational amplifier, a matching resistor R7, a matching resistor R8, a matching resistor R9 and a matching resistor R10; the positive input terminal of the operational amplifier is connected between the bridge resistor R4 and the bridge resistor R0, and the negative input terminal of the operational amplifier is connected between the bridge resistor R5 and the bridge resistor R6; the matching resistor R7 is equal to the matching resistor R8, and the matching resistor R9 is equal to the matching resistor R10.

[0038] In the differential amplification circuit module, the operational amplifier adopts TLV2333, and the mV level differential signal output by the Wheatstone bridge module is amplified by the operational amplifier TLV2333 and then output as a voltage signal with an expected size, which can be directly connected to the AD conversion module. In this application, the signal amplification factor is set to 40 times, the operational amplifier is powered by single 5V, and the differential amplification circuit module is based on rail-to-rail operational amplifier, and the output voltage is 5V. Specifically, the resistance values of the matching resistors R7 and R8 are set to 1kΩ, and the resistance values of the matching resistors R9 and R10 are set to 40kΩ.

[0039] The AD conversion module adopts the following calculation method for acquisition:

[0040] VOUT=(V + -V - )*(R9 / R8)=40*(V + -V - ),

[0041] V + =(VOUT+40*V - ) / 40.

[0042] Wherein, V - is the mV level differential signal output by the Wheatstone bridge module;

[0043] According to the resistance voltage division: R6=82Ω, R4=R5=1kΩ;

[0044] V - ≈227.356mV,

[0045] V + =(VOUT+9094.27) / 40,

[0046] V + =Rpt / (R5+Rpt)*3000,

[0047] Rpt=1000V + / (3000-V + ).

[0048] Rpt is the resistance value corresponding to PT100, and the corresponding temperature value can be obtained by looking up the table.

[0049] Based on the rail-to-rail operational amplifier, when VOUT is 5V, V+=352.356mV, and Rpt=133.08Ω, the range is-46℃~86℃ by looking up the table.

[0050] The application is based on circuit design, can guarantee to meet the use in normal temperature range, improves the precision of measurement because of compressing the temperature range, and the temperature measurement precision can be guaranteed as long as the precision of device selection reaches the requirement. Meanwhile, the circuit of the application is simple, has high stability, high reliability, low cost and great advantages. In actual application, taking the general single-chip microcomputer temperature acquisition as an example, most of the single-chip microcomputers on the market have multi-channel AD acquisition function, generally have more than 8 channels, and the application of the scheme of the application can realize the 8-channel temperature acquisition system only by using 8 measurement circuits, greatly reducing the cost of equipment.

[0051] The above embodiments are only for illustrating the technical concept and characteristics of the application, and the purpose is to enable those skilled in the art to understand the content of the application and implement it, and cannot limit the protection scope of the application. For those skilled in the art, it is obvious that the application is not limited to the details of the above exemplary embodiments, and the application can be implemented in other specific forms without departing from the spirit or basic characteristics of the application, therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-limiting, the scope of the application is defined by the appended claims rather than the above description, therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the application.

Claims

1. A PT100 based narrow range temperature measurement circuit, characterized by, It comprises an input end (1) and an output end (2), a voltage stabilizing module (6), a Wheatstone bridge module (7) and a differential amplification circuit module (8) arranged between the input end (1) and the output end (2); The voltage stabilizing module (6) comprises a voltage stabilizing source (61), voltage stabilizing resistors R2 and R3 arranged in parallel with the voltage stabilizing source (61); The Wheatstone bridge module (7) comprises bridge resistors R4, R5, R6 and R0 arranged in sequence on four bridge arms, wherein the bridge resistor R0 is a resistance value of PT100, and the bridge resistor R4 is equal to the bridge resistor R5; The differential amplification circuit module (8) comprises an operational amplifier (81), matching resistors R7, R8, R9 and R10, wherein the positive input end of the operational amplifier (81) is connected between the bridge resistor R4 and the bridge resistor R0, the negative input end of the operational amplifier (81) is connected between the bridge resistor R5 and the bridge resistor R6, the matching resistor R7 is equal to the matching resistor R8, and the matching resistor R9 is equal to the matching resistor R10.

2. The PT100 based narrow range temperature measurement circuit of claim 1, wherein: In the voltage stabilizing module (6), the voltage stabilizing source (61) adopts TL431, and in combination with the voltage stabilizing resistors R2 and R3, a stable reference voltage is outputted.

3. The PT100 based narrow range temperature measurement circuit of claim 1, wherein: The voltage stabilizing module (6) further comprises a capacitor C3 arranged in parallel.

4. The PT100-based narrow-range temperature measurement circuit of claim 2, wherein: In the differential amplification circuit module (8), the operational amplifier (81) adopts TLV2333, the signal amplification multiple is set to 40 times, and the operational amplifier is powered by single 5V.

5. The PT100 based narrow range temperature measurement circuit of claim 2, wherein: The input end (1) and the voltage stabilizing module (6) are further provided with a filtering module (4) and a voltage dividing module (5).

6. A PT100 based narrow range temperature measurement circuit according to claim 5, wherein: The filtering module (4) comprises capacitors C1 and C2, and the capacitors C1 and C2 are respectively connected in parallel between the input end (1) and a ground end (3). The voltage dividing module (5) comprises a resistor R1 connected in series in the circuit.

7. The PT100 based narrow range temperature measurement circuit of claim 1, wherein: The output end (2) is further connected with an AD conversion module.

8. The PT100 based narrow range temperature measurement circuit of claim 4, wherein: The differential amplification circuit module (8) is based on rail-to-rail operational amplifier, the output voltage is 5V, and the temperature range is -46℃-86℃.

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