SU1613880A1 - Method and apparatus for determining temeperature - Google Patents

Abstract

The invention relates to a measurement technique and makes it possible to improve the accuracy of determining the temperature when using thermal resistance sensors. The thermistor is overheated relative to the temperature of the controlled medium, applying a sawtooth voltage of the form U = √AT, where A is a constant factor, T is the current time, and the temperature of the medium is determined from the measured rise time of the thermistor from zero to level corresponding to the maximum current-voltage characteristics. The number of pulses, counted by the counter 11 for the time interval elapsed from the moment of starting the generator 1 to the maximum voltage on the thermistor 4, is proportional to the temperature of the medium. 2 sec. f-ly, 1 ill.

Description

PP

I-

with

12

The invention relates to a measurement technique and can be used in various systems of automatic temperature control with thermoresistive sensors.

The purpose of the invention is to improve the accuracy of temperature control.

The drawing shows a functional diagram of the device for carrying out the proposed method.

The basis of the proposed method for determining the temperature is the regularity of the change in the maximum point of the static current-voltage characteristic (VAC) of a thermistor that has a section with negative differential resistance, from ambient temperature. In this case, the maximum voltage point UT at the thermistor is determined by the indicated temperature © and the structural parameters of the thermistor according to

. UT, 69 (B - A) A (1) where A. B is the constant coefficients of the temperature characteristic of the thermistor.

If the thermistor is supplied with a saw-tooth voltage varying in time according to the type U, where a is const, then the time interval of the rise of voltage on the thermistor about zero to UT depends only on the ambient temperature 0 to 3.69 N BUT

to

(2)

where And is the dissipation factor of the thermistor, the magnitude of which is determined by the design of the thermistor (dimensions, semiconductor material, etc.).

Measuring the time interval to, you can determine the desired value of ambient temperature 0 directly from relation (2) or from a previously removed calibration dependence.

The proposed method is implemented with a device comprising a sawtooth voltage generator 1, a ban circuit 2, a constant resistor 3, a thermistor 4, a differentiating RC circuit. formed by a capacitor 1 5 and a resistor 6, a control block 7, a trigger 8, an AND 9 coincidence circuit, a counting pulse generator 10, a binary-decimal counter 11, a digital indicator 12. A sawtooth voltage generator 1 is connected via a serial 2 connection.nnig resistor 3 and thermistor 4. The common connection point of resistor 3 and thermistor 4 through a differentiating RC-circuit sub5

ten

15 20

25

0

five

0

5 0 5

is connected to the first input of the trigger 8, the output of which is connected to the control input of the inhibit circuit 2 and the first input of the AND 9 coincidence circuit, to the second input of which the output of the counting pulse generator 10 is connected. The output of the coincidence circuit AND 9 is connected to the information input of the counter 11, the output of which connected (en to the input of the digital indicator 12. The output of the control unit 7, made in the form of the simplest generator of starting pulses, is connected to the second input of the trigger 8 and the control inputs of the generator 1 of the sawtooth voltage and the counter 11.

The device works as follows.

Claims (2)

A short starting impulse from control unit 7 starts generator 1 of sawtooth voltage, trigger 8 and zero counter 11. Generator 1 of sawtooth voltage begins to generate a voltage varying in time according to the indicated dependence U Uat, which comes through an open circuit 2 the prohibition, on the control input of which at this time there is a permitting signal from the output of the trigger 8, to the series-connected resistor 3 and thermistor A. When the voltage on the thermistor increases to Ut, the corresponding its maximum point of the IVC, there is a sharp inrush of current in the circuit of the resistor 3 and thermistor 4. In this case, the differentiating RC circuit forms a short pulse, which kicks on trigger 8 and sets it to its initial state. The output signal of the trigger 8 in this state is zeroed, the enable signal at the control input of the inhibit circuit 2 disappears and, through the inhibit circuit 2, no further voltage is applied to the thermistor 4. The generated output pulse of the trigger 8 is applied to an AND 9 coincidence circuit, the second input of which simultaneously receives short clock pulses from the generator 10 counting pulses. At the output of the coincidence circuit And 9, a packet of clock pulses is formed, the duration of which is proportional to the determined value of the ambient temperature (controlled) environment 0. At a constant frequency of succession of cycles | 9 | x pulses, their number in the packet is also proportional to the determined value of the ambient temperature 0. Formula 1: A method for determining the temperature, consisting in overheating a thermistor placed in a controlled environment. characterized in that, in order to increase the accuracy, the overheating of the thermistor is performed by applying a sawtooth voltage U Va t- to it, where a is a constant factor, t is the current time, and the time interval of the voltage rise on the thermistor is measured to the maximum of its current-voltage characteristic, which determines the temperature of the medium, 2. A device for determining the temperature, containing a thermistor, a constant resistor, a generator of counting pulses, a counter, a digital indicator and a control unit, with the fact that, in order to improve accuracy, a saw-tooth generator is introduced into it differentiating RC circuit, circuit coincidence, the inhibit circuit and the trigger, while the output of the sawtooth generator is connected through the inhibitor circuit to a series-connected thermistor and a constant resistor, whose common point is connected via a differentiating RC circuit to the first trigger input, the output of which is connected to the control input of the inhibitor circuit and the first input of the coincidence circuit, to the second input of which the counting pulse generator output is connected, and the output of the block control unit is connected to the second trigger input and control inputs of the sawtooth voltage generator and counter, whose information input is connected to the output of the coincidence circuit and its output to the input at the digital display.