CN201697727U - Temperature measuring circuit - Google Patents

Abstract

The utility model discloses a temperature measuring circuit comprising a single chip microcomputer, a constant-current source, a resistance Ra between the single chip microcomputer and the constant-current source, wherein the resistance Ra is disposed on the control branch circuit, one end of the resistance Ra being connected to the single chip microcomputer by the control branch circuit, and the other end of the resistance Ra being connected to the constant-current source. The utility model not only shortens working hours of single chip microcomputer, but also decreases time for temperature measuring, combined with reduced power consumption of circuit and energy saving.

Description

A kind of temperature measuring circuit

Technical field

The utility model relates to a kind of metering circuit, relates in particular to a kind of temperature measuring circuit, belongs to the platinum resistance temperature sensor field of measuring technique.

Background technology

At present, though existing temperature measuring circuit can be realized the measurement of temperature, but because whole process constant current source only charges to capacitor C with less current, cause reaching the long during this period of time of predetermined voltage at capacitance voltage, the timer of single-chip microcomputer is the electric energy of meaningless ground consuming cells during this period of time.Existing temperature measurement system (as shown in Figure 1), because there is defective in design, the working time of single-chip microcomputer timer is longer, causes circuit power consumption bigger, causes the waste of the energy.

The utility model content

In order to solve the existing weak point of above-mentioned technology, the utility model discloses a kind of temperature measuring circuit.

In order to solve above technical matters, the technical solution adopted in the utility model is: a kind of temperature measuring circuit, comprise single-chip microcomputer, constant current source, and be provided with resistance R a between single-chip microcomputer and the constant current source, resistance R a is positioned on the control branch road.Resistance R a is connected on the single-chip microcomputer by control branch road one end, and the other end is connected on the constant current source.

The utility model has not only shortened the working time of single-chip microcomputer but also has reduced the thermometric time under the prerequisite that does not influence function, has reduced circuit power consumption, has saved the energy.

Description of drawings

Below in conjunction with the drawings and specific embodiments the utility model is described in further detail.

Fig. 1 is existing temperature measuring circuit schematic diagram.

Fig. 2 is circuit theory diagrams of the present utility model.

Embodiment

As shown in Figure 2, the utility model mainly comprises single-chip microcomputer 1, voltage comparator 2 (CMP), constant current source 3 (being made up of discrete component), control branch road 4, platinum resistance temperature sensor Rb, integrating capacitor C, resistance R a.Increase a resistance R a by single-chip microcomputer 1 control in for constant current source 3 circuit of integrating capacitor C charging, resistance R a is connected on the single-chip microcomputer 1 by control branch road 4 one ends, and the other end is connected (collector of triode Q3 among Fig. 2) on the constant current source 3.Can make the output current of constant current source 3 increase several times by controlling resistance Ra, can improve the electric current of constant current source 3 by this mode at the initial stage of AD conversion (analog to digital conversion), make integrating capacitor C be charged to the starting potential of mating fast with platinum resistance temperature sensor Rb temperature-measuring range, thereby reduced the thermometric time significantly, reduced the power consumption of system.

Platinum resistance: platinum resistance has higher chemical stability, is difficult for being corroded; The reproduction ability that can have very high purity and good electrology characteristic.According to European standard EN60751, the resistance of the platinum resistance temperature sensor formula corresponding with temperature is: (formula 1)

$T=\frac{-R_0\·A+\sqrt{{(R\·A)}^2-4\·B\·(R_0-R)}}{2{\·R}_0\·B}$

In the formula: R---the resistance value that records, Ω;

T---calculated temperature, ℃;

R ₀, A, predetermined parameter among B---the IEC 60751.

Platinum resistance has Pt10, Pt100, and Pt1000 etc., its resistance varies with temperature and the approximately linear variation, and each resistance correspondence unique temperature.Here be that example is introduced with standard platinum resistance temperature sensor Pt1000.In the time of 0 ℃, its resistance is about 1000 Ω, and in the time of 100 ℃, its resistance is about 1385 Ω.

Constant current source: have two constant current sources in the metering circuit, its effect is respectively: one. give standard platinum resistance temperature sensor Rb input steady current, therefore, on platinum resistance temperature sensor Rb, can produce a voltage (this voltage is linear change with the change of Rb resistance), this voltage is designated as URb.URb is access in the end of voltage comparator CMP.Two. give integrating capacitor C with constant current charge, before reaching the rated voltage of electric capacity, the voltage of integrating capacitor C increases in time and is linear and raises, and this voltage is designated as UC.UC is access in the other end of voltage comparator CMP.

Measuring principle: when carrying out temperature survey, constant current source is given standard platinum resistance temperature sensor Rb input steady current, and Rb is last can to produce voltage U Rb; Simultaneously, constant current source is given integrating capacitor C charging, and the voltage U C of integrating capacitor C raises gradually.The timer of single-chip microcomputer picks up counting.When UC=URb, comparator output signal, timer stops timing.The timing time of timer is the duration of charging t of electric capacity at this moment.The temperature difference of measuring, the resistance of standard platinum resistance temperature sensor Rb are just different, will cause the duration of charging t difference of electric capacity.Their linear approximate relationships.Single-chip microcomputer just can calculate the standard platinum resistance temperature of this moment according to the duration of charging of electric capacity, is revised just to draw temperature value more accurately again.

The calculating of temperature: above mention, standard platinum resistance temperature sensor Pt1000 is in the time of 0 ℃, and its resistance is about 1000 Ω, and in the time of 100 ℃, its resistance is about 1385 Ω.And the electric current that constant current source provides to Rb is 1mA, and so, the voltage range that produces on the Rb in the time of 0 ℃-100 ℃ is about 1V-1.385V.We use t _{0 ℃}And t _{100 ℃}Represent that respectively electric capacity is charged to 1V and used time of 1.385V.When the Rb temperature change, we have measured another time t _bThe time, we just can obtain t _bThe resistance R of pairing Rb is: (formula 2)

R＝((t _b-t _0℃)/(t _100℃-t _0℃))*(100℃-0℃)

Just can calculate measured temperature value in conjunction with formula 1 again.

The realization of low-power consumption: we see in the calculating of temperature, use in the calculating actual be the difference of timing value, and be not timing value itself.Therefore, integrating capacitor C from 0V be charged to 1V use during this period of time less than, but it has but taken almost 2/3 timing, single-chip microcomputer and timer are all flogging a dead horse during this period of time.In order to reduce the time that single-chip microcomputer and timer flog a dead horse, we have increased a control branch road (branch road 4 among Fig. 2) to constant current source, in thermometric early stage, make the constant current source conducting with the control branch road that increases, give integrating capacitor C rapid charge with big electric current, reduced the timing time of single-chip microcomputer timer.When integrating capacitor C charges to the starting potential of mating with the platinum resistance temperature sensor temperature-measuring range, close the control branch road of increase, use the small electric current charge instead.Though integrating capacitor C charging electric current in earlier stage increases, total electric weight that charges is constant, therefore, does not have the additive decrementation electric energy.But the timer part, the total timing of timer shortens, and electric energy has been saved in the also corresponding shortening of single-chip microcomputer working time.Therefore, the circuit total power consumption reduces.

For the better novel energy-saving effect of this use of explanation, following table is the comparison (the employed single-chip microcomputer of above-mentioned experiment is the MSP430 series monolithic, thermometric interval time be 8 seconds) of the related data of the utility model and existing temperature measuring circuit:

The temperature measuring circuit that increases constant current source control branch road has been replaced existing temperature measuring circuit, under the prerequisite that does not influence function, greatly reduces the power consumption of circuit, has saved the energy.

Claims (2)

1. a temperature measuring circuit comprises single-chip microcomputer, constant current source, it is characterized in that: be provided with resistance R a between described single-chip microcomputer and the constant current source, resistance R a is positioned on the control branch road.

2. temperature measuring circuit according to claim 1 is characterized in that: described resistance R a is connected on the single-chip microcomputer by control branch road one end, and the other end is connected on the constant current source.

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