CN202171514U - circuit by utilizing double-constant current source - Google Patents

Abstract

Provided is a three-way temperature platinum resistance measuring <{EN0}>circuit by utilizing double-constant current source, relating to precision temperature platinum resistance measuring field and comprising a platinum resistor (RTD) to be detected, a first lead RL1, a second lead RL2, a third lead RL3, a reference resistor RREF, a power supply GND, a first constant current source IOUT1, a second constant source IOUT2 and an analog-to-digital conversion circuit; output terminals of the two constant current sources are first respectively in connection with two differential input terminals of the analog-to-digital conversion circuit and then are in connection with one end of the RTD to be detected through leads; the other end of the RTD to be detected is in connection with one end of the reference resistor through leads and meanwhile is in connection with a reference voltage positive terminal of the analog-to-digital conversion circuit; the other end of the reference voltage is in connection with a reference voltage negative terminal of the analog-to-digital conversion circuit and the GND. The circuit of the utility model can eliminate the influence to real results caused by lead resistance and constant current source fluctuation; the circuit is simple and the cost is low.

Description

A kind of circuit that utilizes the two three-way measurement temperature of constant current source RTDs

Technical field

The utility model relates to precision temperature RTD field of measurement, is specifically related to a kind of circuit that utilizes the two three-way measurement temperature of constant current source RTDs.

Background technology

1), the two-wire system measuring method at present, known high-precision temperature RTD measuring method has four kinds:; 2), common three-wire system measuring method; 3), constant voltage partial pressure type three-wire system measuring method; 4), Kelvin's four line measuring methods.More than measuring accuracy, applicable situation, the measuring equipment manufacturing cost of four kinds of methods have nothing in common with each other.Wherein, first three methods can't be eliminated the influence of conductor resistance to measuring accuracy fully.Have only the 4th kind of Kelvin four line measuring method precision the highest; Can eliminate the influence of conductor resistance fully to actual thermometric; But measurement mechanism is complicated, manufacturing cost is high; Need instrument and meter amplifier, constant current source need compensate or metering circuit like differential input terminal, analog-to-digital conversion circuit needs the standard of precision voltage source.Therefore, provide a kind of circuit simple in structure, cost is low, precision is high measurement temperature RTD imperative.

The utility model content

In order to overcome the problem that existing high-precision temperature RTD measurement mechanism is complicated, measuring accuracy is low; The utility model provides a kind of circuit that utilizes the two three-way measurement temperature of constant current source RTDs; Can not only eliminate the influence of conductor resistance, constant current source drift to actual thermometric; And measurement mechanism is simple in structure, low cost of manufacture.

The technical scheme that the utility model technical solution problem is adopted is following:

A kind of circuit that utilizes the two three-way measurement temperature of constant current source RTDs comprises tested RTD RTD, the first lead R _L1, the second lead R _L2, privates R _L3, reference resistance R _REF, power supply ground GND, the first constant current source I _OUT1, the second constant current source I _OUT2And analog-to-digital conversion circuit; The second lead R _L2With privates R _L3An end be connected the other end of tested RTD RTD and the first lead R with the same end of tested RTD RTD _L1An end connect; The first constant current source I _OUT1Output terminal be connected to the differential positive input terminal AIN of analog-to-digital conversion circuit earlier ₊, be connected to the first lead R _L1The other end; The second constant current source I _OUT2Output terminal be connected to the differential negative input end AIN of analog-to-digital conversion circuit earlier _-, be connected to the second lead R _L2The other end; Reference resistance R _REFBe connected respectively to the reference voltage anode REFIN of analog-to-digital conversion circuit ₊With reference voltage negative terminal REFIN _-Privates R _L3The other end be connected to the reference voltage anode REFIN of analog-to-digital conversion circuit ₊, the reference voltage negative terminal REFIN of analog-to-digital conversion circuit _-Be connected to the power supply ground GND of analog-to-digital conversion circuit.

The beneficial effect of the utility model is: do not need instrument and meter amplifier and accurate reference voltage, can high-acruracy survey goes out the resistance value of temperature RTD RTD, and simple in structure.

Description of drawings

Fig. 1 is the circuit theory diagrams that the utility model utilizes the two three-way measurement temperature of constant current source RTDs.

Embodiment

Below in conjunction with accompanying drawing and embodiment the utility model is explained further details.

As shown in Figure 1, the circuit of the two three-way measurement temperature of the constant current source RTDs of the utility model utilization comprises: tested RTD RTD, the first lead R _L1, the second lead R _L2, privates R _L3, reference resistance R _REF, power supply ground GND, the first constant current source I _OUT1, the second constant current source I _OUT2And analog-to-digital conversion circuit.

Because the first constant current source I _OUT1Output terminal and the differential positive input terminal AIN of analog-to-digital conversion circuit ₊Link together, so 2 current potentials equate.The magnitude of voltage that this puts relative power supply ground GND is the first constant current source I _OUT1The whole current return of flowing through, each components and parts produces the algebraic sum of voltage difference.The known first constant current source I _OUT1The first lead R flows through _L1, tested RTD RTD, privates R _L3, reference resistance R _REF, so the voltage difference algebraic sum that produces is:

U_AIN ₊＝I _OUT1×R _L1+I _OUT1×RTD+I _OUT1×R _L3+I _OUT1×R _REF。

Because the second constant current source I _OUT2Output terminal and the differential negative input end AIN of analog-to-digital conversion circuit _-Link together, so 2 current potentials equate.The magnitude of voltage that this puts relative power supply ground GND is the second constant current source I _OUT2The whole current return of flowing through, each components and parts produces the algebraic sum of voltage difference.The known second constant current source I _OUT2The second lead R flows through _L2, privates R _L3, reference resistance R _REF, so the voltage difference algebraic sum that produces is:

U_AIN _-＝I _OUT2×R _L2+I _OUT2×R _L3+I _OUT2×R _REF。

The differential positive input terminal AIN of analog-to-digital conversion circuit ₊With negative input end AIN _-Between electric potential difference U_AIN, be differential positive input terminal AIN ₊The magnitude of voltage U_AIN of relative power supply ground GND ₊, deduct differential negative input end AIN _-The magnitude of voltage U_AIN of relative power supply ground GND _-

U_AIN＝U_AIN ₊-U_AIN _-＝(I _OUT1×R _L1+I _OUT1×RTD+I _OUT1×R _L3+I _OUT1×R _REF)-(I _OUT2×R _L2+I _OUT2×R _L3+I _OUT2×R _REF)。

The first constant current source I _OUT1, the second constant current source I _OUT2The output current basically identical, so current value I _OUT1≈ I _OUT2Three lead first lead R _L1, the second lead R _L2, privates R _L3Material, length are the same, so resistance value R _L1≈ R _L2≈ R _L3

So U_AIN=I behind the cancellation identical entry _OUT1* RTD explains that the magnitude of voltage U_RTD of measured RTD RTD is equal to the differential positive input terminal U_AIN through the analog-to-digital conversion circuit after the lead transmission, U_RTD=U_AIN, the i.e. first lead R _L1With the second lead R _L2The error of bringing is by cancellation, the only remaining uncertain factor first constant current source I _OUT1With the second constant current source I _OUT2

The first constant current source I _OUT1The reference resistance R of measured RTD RTD and the known resistance of flowing through _REF, the second constant current source I _OUT2The reference resistance R of the known resistance of flowing through _REF

Because it is verified: U_AIN=U_RTD=I _OUT1* RTD.

U_R _REF＝(I _OUT1+I _OUT2)×R _REF。

So $\frac{U\_\mathrm{RTD}}{U\_R_{\mathrm{REF}}}=\frac{\mathrm{RTD}*I_{\mathrm{OUT}1}}{R_{\mathrm{REF}}*(I_{\mathrm{OUT}1}*I_{\mathrm{OUT}2})}=\frac{\mathrm{RTD}}{R_{\mathrm{REF}}*2}.$

The first constant current source I of this system _OUT1, the second constant current source I _OUT2Simultaneously disappeared, proved that the constant current source fluctuation is to not influence of measurement result.

In this formula, reference resistance R _REFKnown, U_AIN, U_R _REFCan record through analog-to-digital conversion circuit,, and get rid of the influence of constant current source fluctuation, conductor resistance so RTD RTD can accurately calculate out.

Claims (1)

1. a circuit that utilizes the two three-way measurement temperature of constant current source RTDs is characterized in that this circuit comprises tested RTD RTD, the first lead R _L1, the second lead R _L2, privates R _L3, reference resistance R _REF, power supply ground GND, the first constant current source I _OUT1, the second constant current source I _OUT2And analog-to-digital conversion circuit; The second lead R _L2With privates R _L3An end be connected the other end of tested RTD RTD and the first lead R with the same end of tested RTD RTD _L1An end connect; The first constant current source I _OUT1Output terminal be connected to the differential positive input terminal AIN of analog-to-digital conversion circuit earlier ₊, be connected to the first lead R _L1The other end; The second constant current source I _OUT2Output terminal be connected to the differential negative input end AIN of analog-to-digital conversion circuit earlier _-, be connected to the second lead R _L2The other end; Reference resistance R _REFBe connected respectively to the reference voltage anode REFIN of analog-to-digital conversion circuit ₊With reference voltage negative terminal REFIN _-Privates R _L3The other end be connected to the reference voltage anode REFIN of analog-to-digital conversion circuit ₊, the reference voltage negative terminal REFIN of analog-to-digital conversion circuit _-Be connected to the power supply ground GND of analog-to-digital conversion circuit.

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