PT100 temperature detection circuit

Abstract

The invention discloses a PT100 temperature detection circuit which comprises a constant current source module, a voltage transfer module, a lead resistance elimination module and a proportion adjustment output module which form the circuit. The constant current source module comprises a first transistor, a first resistor, a second transistor and a second resistor; the voltage transfer module and the lead resistance elimination module comprise a first reverse proportional amplification circuit and a first in-phase proportional amplification circuit; the proportion adjustment output module comprises a second in-phase proportion amplification circuit and a second reverse proportion amplification circuit which are connected in series. According to the invention, the voltage on the lead resistor can be completely eliminated, and meanwhile, the full-scale voltage from 0V to AD sampling can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of temperature measurement circuits, and in particular to a PT100 temperature detection circuit. Background Art

[0002] The existing PT100 temperature measurement circuit usually uses series voltage division, differential bridge and other circuits to sample the voltage. After the small signal is amplified and regulated, it is sent to the ADC port for collection and data processing. This processing method has many disadvantages:

[0003] 1. The existing PT100 temperature sampling circuit connection method usually does not fully utilize the ADC range due to the existence of voltage division.

[0004] 2. The existing sampling circuit will divert part of the current in the measurement circuit, affecting the accuracy of the sampling circuit.

[0005] 3. If the sampling loop of the existing sampling circuit is long, the wiring resistance and line resistance will be introduced into the measurement, further reducing the accuracy of the sampling loop. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a PT100 temperature detection circuit, which can completely eliminate the voltage on the lead resistance and realize the full-scale voltage from 0V to AD sampling.

[0007] In order to solve the above technical problems, the present invention provides a PT100 temperature detection circuit, including a constant current source module, a voltage transfer module, a lead resistance elimination module and a proportional adjustment output module constituting the circuit;

[0008] The constant current source module includes a first transistor, a first resistor, a second transistor and a second resistor, and the voltage transfer module and the lead resistance elimination module include a first reverse proportional amplifier circuit and a first in-phase proportional amplifier circuit;

[0009] The proportional adjustment output module includes a second in-phase proportional amplifier circuit and a second inverse proportional amplifier circuit connected in series.

[0010] Furthermore, the output end of the proportional adjustment output module is also provided with a first diode, a third resistor and a first capacitor.

[0011] Furthermore, when the constant current source module adopts a two-wire connection, the parameters flowing toward the first resistor are:

[0012]

[0013] V1=Vref+VRx+Vpt+VRx;

[0014] Vp=Vref-(V1-Vref).

[0015] Furthermore, the output voltage of the first reverse proportional amplifier circuit is:

[0016] Vp=Vref-((Vref+VRx+Vpt+VRx)-Vref)

[0017] =Vref-(Vref+VRx+Vpt+VRx-Vref)

[0018] =Vref-Vref+Vref-Vpt-VRx-VRx

[0019] =Vref-Vpt-2VRx;

[0020] Among them, the lead resistance can be ignored, that is: Vp = Vref-Vpt;

[0021] The output voltage of the first in-phase proportional amplifier circuit is: Vn=2Vref.

[0022] Furthermore, the output voltage of the second in-phase proportional amplifier circuit is:

[0023] Vo = Vref (1-N) - Vpt (1+N);

[0024] Where Vref is fixed, Vpt is the voltage across PT100, and N is the amplification factor;

[0025] in,

[0026] Let Vo = 0, and bring in the resistance value at 0V to determine the value of the amplifying resistor R30 / R29.

[0027] The final output voltage is:

[0028]

[0029] Furthermore, the output voltage of the second reverse proportional amplifier circuit is:

[0030] Substitute PTmax into the Vomax at the highest temperature to determine the value of the amplifying resistor R33 / R32:

[0031] Finally, the complete output formula is obtained:

[0032]

[0033] Furthermore, when the constant current source module adopts three-wire wiring,

[0034] Vp=(Vref+VRx)-((Vref+VRx+Vpt+VRx)-(Vref+VRx))

[0035] =Vref+VRx-(Vref+VRx+Vpt+VRx-Vref-VRx)

[0036] =Vref+Vref-Vref-Vpt+VRx+VRx-VRx-VRx

[0037] =Vref-Vpt.

[0038] Beneficial effects of the present invention: Compared with the prior art, the present invention can completely eliminate the voltage on the lead resistance and can achieve a full-scale voltage from 0V to AD sampling. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is the overall circuit diagram of the present invention.

[0040] Figure 2 It is a two-wire principle schematic diagram of the present invention.

[0041] Figure 3 It is a three-wire principle schematic diagram of the present invention.

[0042] Explanation of the reference numerals in the figure: Q2, first transistor; R25, first resistor; U12, second transistor; R24, second resistor; D2, first diode; R39, third resistor; C40, first capacitor. DETAILED DESCRIPTION

[0043] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0044] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0045] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0046] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0047] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0048] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only implementation method.

[0049] Reference Figure 1As shown, an embodiment of a PT100 temperature detection circuit of the present invention, a PT100 temperature detection circuit, characterized in that it includes a constant current source module, a voltage transfer module, a lead resistance elimination module and a proportional adjustment output module that constitute the circuit; the constant current source module includes a first transistor Q2, a first resistor R25, a second transistor U12 and a second resistor R24, the voltage transfer module and the lead resistance elimination module include a first reverse proportional amplifier circuit and a first in-phase proportional amplifier circuit; the proportional adjustment output module includes a second in-phase proportional amplifier circuit and a second reverse proportional amplifier circuit connected in series.

[0050] The functions of each part are as follows: Constant current source module: provides a bias current for the external circuit.

[0051] Voltage transfer module: samples the voltage on the resistor almost losslessly to the subsequent calculation circuit.

[0052] Lead resistance elimination module: eliminates the introduced lead resistance voltage and then amplifies it proportionally.

[0053] Proportional output module: adjusts the output to the voltage amplitude we need and then outputs it.

[0054] It is suitable for two-wire and three-wire PT100 temperature measurement circuits. For two-wire, connect the 1st and 2nd pins of H4, and short-circuit PAN2 on the board. For three-wire, connect the common end of PT100 to the 2nd and 3rd pins of H4, and the other end to the 1st pin of H4.

[0055] The overall design idea is as follows: the resistance of PT100 will change with the change of temperature. At this time, a constant current source can be used to pass a stable current through it, and a voltage value that changes with the temperature will be generated at both ends of it. At this time, what needs to be done is to read this voltage for processing.

[0056] When the lead is too long, the resistance of the lead will also cause a voltage drop. Because we cannot directly collect the voltage across the resistor, we need to subtract twice the voltage value on one lead from the voltage value collected at the port.

[0057] Then we need to adjust the remaining voltage to a suitable ratio, that is, when the lowest temperature we define is 0V, and when the maximum temperature is 3V, the subsequent amplification factor is determined.

[0058] When two lines are working (reference Figure 2 ):

[0059] Q2, R25, U12, and R24 form a constant current source circuit to power PT100. R35 cannot be welded.

[0060] The current from Q2 goes all the way down, flows through PT100, and goes all the way to the right to the amplifier circuit. The current in the branch going down is a constant value:

[0061]

[0062] V1=Vref+VRx+Vpt+VRx

[0063] Vp=Vref-(V1-Vref)

[0064] The U17.1 op amp forms a reverse proportional amplifier circuit, and the output voltage is:

[0065] Vp=Vref-((Vref+VRx+Vpt+VRx)-Vref)

[0066] =Vref-(Vref+VRx+Vpt+VRx-Vref)

[0067] =Vref-Vref+Vref-Vpt-VRx-VRx

[0068] =Vref-Vpt-2VRx

[0069] The two-wire wiring method inevitably introduces lead resistance, so we can ignore the lead resistance during analysis.

[0070] Vp=Vref-Vpt

[0071] The U17.2 op amp forms a single in-phase proportional amplifier, and the output voltage is:

[0072] Vn=2Vref

[0073] This is to eliminate the impact of level drift caused by the introduction of Vref

[0074] The output voltage of U18.1 op amp is:

[0075]

[0076] The output voltage is:

[0077] Vo=Vref(1-N)-Vpt(1+N)

[0078] Among them, Vref is fixed, Vpt is the voltage across PT100, and N is the amplification factor; it can be found that this circuit can output positive and negative voltage.

[0079]

[0080] Let Vo = 0, and at the same time bring in the resistance value at 0V that we defined, and determine the value of the amplifying resistor R30 / R29. This is to eliminate the voltage offset and determine the 0 point of the operating voltage.

[0081]

[0082] Note: PTo is the resistance value of PT100 corresponding to the temperature when the output is 0V.

[0083] The complete output formula for Vo is:

[0084]

[0085] Determine its output range: Vo1max, at this time PT100 corresponds to the resistance value PTmax at the maximum temperature

[0086] U18.2 is a reverse proportional amplifier circuit, and the output voltage is:

[0087]

[0088] Substitute PTmax into the Vomax at the highest temperature to determine the value of the amplifier resistor R33 / R32

[0089]

[0090] Determine the magnification of the last stage N1

[0091] The final complete output voltage formula is:

[0092]

[0093] It can be seen from the above formula that the resistance is a fixed value, the voltage is also a reference voltage, and the final output voltage is only related to the resistance value of PT100 itself.

[0094] When three-wire PT100 (reference Figure 3 ):

[0095] The current direction is the same as that of two-wire case, so PAN2 needs to be disconnected and R35 cannot be welded.

[0096] At this time, we need to pay attention to the voltage of Vp:

[0097] V2=Vref+VRx

[0098] V1=Vref+VRx+Vpt+VRx

[0099] Vp=V2-(V1-V2)

[0100] Combining the above three formulas, we can get:

[0101] Vp=(Vref+Vx)-((Vref+VRx+Vpt+VRx)-(Vref+VRx))

[0102] =Vref+VRx-(Vref+VRx+Vpt+VRx-Vref-VRx)

[0103] =Vref+Vref-Vref-Vpt+VRx+VRx-VRx-VRx=Vref-Vpt

[0104] Comparison with two-wire wiring

[0105] Vp=Vref-((Vref+VRx+Vpt+VRx)-Vref)

[0106] =Vref-(Vref+VRx+Vpt+VRx-Vref)

[0107] =Vref-Vref+Vref-Vpt-VRx-VRx

[0108] =Vref-Vpt-2VRx

[0109] It can be seen that this part of the circuit completely eliminates the influence of the lead resistance, and the output voltage of Vp is the precise reference voltage - the voltage on PT100. The rest of the calculation method is the same as the two-wire operation, so it will not be repeated here.

[0110] The final output D2, R39, and C40 are for output protection and filtering to prevent overvoltage damage to the rear sampling chip caused by excessive output voltage when PT100 is not connected and to filter out high-frequency interference.

[0111] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A PT100 temperature detection circuit, characterized in that: It includes a constant current source module, a voltage transfer module, a lead resistance elimination module and a proportional adjustment output module which constitute the circuit; The constant current source module includes a first transistor (Q2), a first resistor (R25), a second transistor (U12) and a second resistor (R24); the voltage transfer module and the lead resistance elimination module include a first reverse proportional amplification circuit and a first in-phase proportional amplification circuit; The proportional adjustment output module includes a second in-phase proportional amplifier circuit and a second inverse proportional amplifier circuit connected in series.

2. The PT100 temperature detection circuit according to claim 1, characterized in that: The output end of the proportional adjustment output module is also provided with a first diode (D2), a third resistor (R39) and a first capacitor (C40).

3. The PT100 temperature detection circuit according to claim 1, characterized in that: When the constant current source module adopts two-wire wiring, the parameters flowing toward the first resistor are: V1=Vref-VRx+Vpt+VRx; Vp=Vref-(V1-Vref).

4. The PT100 temperature detection circuit according to claim 1, characterized in that: The output voltage of the first reverse proportional amplifier circuit is: Vp=Vref-((Vref+VRx+Vpt+VRx)-Vref) =Vref-(Vref+VRx+Vpt+VRx-Vref) =Vref-Vref+Vref-Vpt-VRx-VRx =Vref-Vpt-2VRx: Among them, the lead resistance can be ignored, that is: Vp = Vref-Vpt; The output voltage of the first in-phase proportional amplifier circuit is: Vn=2Vref.

5. The PT100 temperature detection circuit according to claim 1, characterized in that: The output voltage of the second in-phase proportional amplifier circuit is: Vo = Vref (1-N) - Vpt (1+N): Where Vref is fixed, Vpt is the voltage across PT100, and N is the amplification factor; in, Let Vo = 0, and bring in the resistance value at 0V to determine the value of the amplifying resistor R30 / R29. The final output voltage is:

6. The PT100 temperature detection circuit according to claim 1, characterized in that: The output voltage of the second reverse proportional amplifier circuit is: Substitute PTmax into the Vomax at the highest temperature to determine the value of the amplifying resistor R33 / R32: Finally, the complete output formula is obtained:

7. The PT100 temperature detection circuit according to claim 1, characterized in that: When the constant current source module adopts three-wire wiring, Vp=(Vref+VRx)-((Vref+VRx+Vpt+VRx)-(Vref+VRx)) =Vref+VRx-(Vref+VRx+Vpt+VRx-Vref-VRx) =Vref+Vref-Vref-Vpt+VRx+VRx-VRx-VRx =Vref-Vpt.

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