PT100 measuring circuit

Abstract

The utility model belongs to the technical field of flue gas measurement. The utility model provides a PT100 measuring circuit. The PT100 measuring circuit comprises a bridge unit, a charge release unit and a wiring fault judgment unit, the bridge unit comprises an R4, an R5, an R6 and a PT100; the R4 and the PT100 form a left half bridge, and the R5 and the R6 form a right half bridge; the charge release unit comprises a D1 charge release channel and a D2 charge release channel; one end of the D1 charge release channel is connected to a line between the R4 and the PT100 of the left half bridge; one end of the D2 charge release channel is connected to a line where the R5 and the R6 of the right half bridge are located; the wiring fault judgment unit comprises an OR gate chip U3, an OR gate chip R8 and an OR gate chip R9; the other end of the R8 and the other end of the R9 are respectively connected with an input port of the gate chip U3, one end of the R8 is connected with a point A of the bridge unit, and one end of the R9 is connected with a point B of the bridge unit. The circuit is simple, reliable and high in universality; meanwhile, the device is used for detecting faults of the PT100 in the transportation, installation and use processes.

Description

Technical Field

[0001] The utility model belongs to the technical field of flue gas measurement. Background Art

[0002] Continuous Emission Monitoring Systems (CEMS) require continuous measurement of flue gas temperature to calculate pollutant emissions. The PT100 platinum RTD, whose resistance increases with temperature, offers advantages such as high accuracy, good consistency, a wide temperature range, and strong reliability. It is widely used in industrial temperature measurement and is also widely used for flue gas measurement in CEMS.

[0003] During the flue gas temperature measurement process, the probe will gradually accumulate charge due to gas friction. When the charge reaches a certain amount, it will discharge through the measurement circuit, breaking down electronic components such as the operational amplifier in the measurement circuit. At the same time, due to the high temperature and corrosive nature of flue gas, the PT100 is more likely to be damaged. That is, in the scenario of measuring flue gas temperature: First, the friction between flue gas and the probe gradually accumulates charge. When the charge accumulates to a sufficient amount, there is a certain probability that it will discharge through the PT100 to the measurement circuit, causing damage to the components connected to it; Second, the high measurement temperature and the corrosive nature of flue gas increase the probability of damage to the PT100. Utility Model Content

[0004] In view of this, the present invention provides a PT100 measurement circuit, comprising: a bridge unit, a charge release unit and a wiring fault judgment unit; the bridge unit comprises: R4, R5, R6 and PT100; the R4 and PT100 constitute a left half bridge, and the R5 and R6 constitute a right half bridge; the charge release unit comprises: a D1 charge release channel and a D2 charge release channel; one end of the D1 charge release channel is connected to the line between R4 and PT100 of the left half bridge; one end of the D2 charge release channel is connected to the line where R5 and R6 of the right half bridge are located; the wiring fault judgment unit comprises an OR gate chip U3, R8 and R9; the other ends of R8 and R9 are respectively connected to the input port of the gate chip U3, one end of R8 is connected to point A of the bridge unit, and one end of R9 is connected to point B of the bridge unit.

[0005] Furthermore, D1 and D2 are TVS.

[0006] This circuit is simple, reliable, and versatile. It can be used in digital circuits, with the central processor measuring temperature through the ADC. It can also be used in analog circuits, collecting temperature signals at the front end of the transmitter and outputting analog signals such as 4-20mA, 0-5V, and 0-10V after circuit adjustment. It can also be used to detect PT100 faults caused by loose leads or disconnections during transportation, installation, and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is a constant voltage circuit, where VREF is the constant voltage source output and U1 is a precision voltage source chip.

[0008] Figure 2 It is a PT100 measurement circuit.

[0009] Figure 3 It is a PT100 fault detection circuit. DETAILED DESCRIPTION

[0010] Example

[0011] The utility model improves the existing PT100 measurement circuit according to the characteristics of flue gas temperature measurement, adds an anti-static protection circuit at the measurement entrance, and adds a detection circuit to deal with PT100 failure and loose wiring, and can send a fault signal when a problem occurs with PT100.

[0012] The design circuit provided by the utility model adopts a constant voltage circuit and a PT100 three-wire bridge measurement circuit, and has the advantages of simple circuit structure, stability and reliability, low cost and high precision.

[0013] The PT100 measuring circuit provided by the utility model comprises: a bridge unit, a charge release unit and a wiring fault judgment unit.

[0014] The charge release unit includes two TVS (transient voltage suppressors), such as Figure 2 The D1 and D2 charge release channels in the circuit serve as charge release channels for external probes. Their other ends are connected to the ALG, protecting measurement chips like U2. One end of the D1 charge release channel connects to the line between R4 and PT100 on the left half of the bridge; one end of the D2 charge release channel connects to the line between R5 and R6 on the right half of the bridge. D1 and D2 are transient voltage suppressors (TVSs).

[0015] The bridge unit includes R4, R5, R6, and a PT100. RL1, RL2, and RL3 represent the PT100 lead resistances. The three PT100 leads have the same specifications and lengths: RL1 = RL2 = RL3. To prevent heating during PT100 measurement, the current flowing through the bridge must be controlled within 1mA. R4 and the PT100 form the left half of the bridge, while R5 and R6 form the right half. The currents in both bridges are within 1mA. The current passing through RL1 is equal to the sum of the currents in the left and right bridge arms, which is within 2mA. Therefore, VOS < 2mA x RL1. Since RL1 and the current flowing through the bridge are very small, VOS can be considered to be at the same potential as ALG, i.e., VOS = ALG.

[0016] Among them, the left half bridge Right half bridge

[0017] Among them, U2 is the instrument amplifier, R7 configures the amplification factor, and if the amplification factor is m, the amplifier output Take R4=R5=4K, R6=100Ω. Considering that R4 is much larger than PT100 or R6, it plays a decisive role in the denominator. Under the condition of meeting the accuracy, the two denominators can be considered equal (R4+PT100+RL3)=(R5+R6+RL2)=Z.

[0018] therefore,

[0019] This eliminates the influence of the line resistance in the numerator. At the same time, RL2 and RL3 in the denominator are much smaller than the other addends, so the influence of the line resistance in the denominator can be ignored. Therefore, the formula can be simplified to:

[0020]

[0021] Solving for PT100:

[0022] In this way, the resistance value of PT100 can be calculated by measuring VPT, and then the temperature of PT100 can be calculated by looking up the table.

[0023] The wiring fault judgment unit includes an OR gate chip U3, R8 and R9; the other ends of R8 and R9 are respectively connected to the input port of the gate chip U3, one end of R8 is connected to point A of the bridge unit, and one end of R9 is connected to point B of the bridge unit. Figure 2 and Figure 3 shown.

[0024] The table below lists U3 output levels for various wiring faults. When the PT100 wiring is normal, CHECKPT outputs a low level, while when a fault occurs, it outputs a high level. If VREF is limited to the processor's IO voltage range, CHECKPT can be connected directly to the processor. The processor can detect PT100 wiring faults by determining the high and low levels of CHECKPT.

[0025]

[0026]

[0027] This circuit is simple, reliable, and versatile. It can be used in digital circuits, with the central processor measuring temperature through the ADC. It can also be used in analog circuits, collecting temperature signals at the front end of the transmitter and outputting analog signals such as 4-20mA, 0-5V, and 0-10V after circuit adjustment. It can also be used to detect PT100 faults caused by loose leads or disconnections during transportation, installation, and use.

Claims

1. PT100 measurement circuit, which is characterized by, include: Bridge unit, charge release unit and wiring fault judgment unit; The bridge unit includes: R4, R5, R6 and PT100; R4 and PT100 constitute the left half bridge, and R5 and R6 constitute the right half bridge; The charge release unit includes: a D1 charge release channel and a D2 charge release channel; one end of the D1 charge release channel is connected to the line between R4 and PT100 of the left half bridge; one end of the D2 charge release channel is connected to the line where R5 and R6 of the right half bridge are located; The wiring fault judgment unit includes an OR gate chip U3, R8 and R9; the other ends of R8 and R9 are respectively connected to the input port of the gate chip U3, one end of R8 is connected to point A of the bridge unit, and one end of R9 is connected to point B of the bridge unit.

2. The PT100 measuring circuit according to claim 1, wherein: The D1 and D2 are TVS.

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