SU1204967A1 - Device for measuring temperature - Google Patents

Description

f

The invention relates to the field of temperature measurement and can be used in the construction of high-precision, high-speed means of measuring the temperature of surfaces of hard-to-reach objects.

The purpose of the invention is to improve the accuracy of measurement with increased speed.

FIG. 1 shows the sensor of the heat flux of the device; FIG. 2 is a block diagram of the device j in FIG. 3 is a diagram of a square root extraction unit.

The device contains a heat flux sensor, which consists of a sensing element 1, for example, thermoelectric converters are used, which contact through a sample heat-conducting plate 2 with a heater 3, which are housed in a heat insulating housing 4.

The sensing element of the sensor is connected to the input of the 5-DC amplifier, the output of which is connected to the same input of the unit as compared to. NIN 6, the second input of which is connected to the output of the source of the reference voltage 7, which together with the comparison unit serves to set the lower limit of the temperature measurement. In the particular case, the zero level can be used as a reference voltage supplied to the second input of the Comparison Unit -6. The output of the comparison unit is connected to the output of the device, as well as through the square root extraction unit 8 and the power amplifier 9, connected to the heater 3 of the sensor.

The device works as follows.

After contact of the object under study and sensor T (the device’s exhalation flux at the last output appears, the emf is caused by the temperature difference between the object and the heat-conducting plate 2. This emf is amplified by the dc amplifier 5, the output voltage of which is compared with the reference voltage from the source 7 of the reference voltage by means of the comparison unit 6, the output signal of which is fed through the block 8 and the power amplifier 9 to the heater 3, the heat released causes the alignment

12049672

temperature of the object and the heat-conducting plate 2. This leads to a decrease in the output EMF of the Heat Flow sensor. When achieving equality

5 of the converted temperature and the temperature of the heat conducting plate 2, which is provided by a large gain value of the amplifier 5, this EMF tends to zero, and

And, therefore, the static error of the device also tends to be zero.

The use of the square-root extraction unit 8 in the negative feedback circuit is due to

15 by the necessity of obtaining a linear dependence of the output voltage on the measured temperature Tu, With an equal temperature of the object T; temperature generated by the heater

20 T, it is proportional to the power given off by the heater, i.e.

k. R "

t - t

 X - No.

(one)

25 where

k - coefficient of proportionality j

UH and Rj, are respectively the voltage across the heater and its resistance.

thirty

To obtain a linear relationship between the output voltage of the device generated at the output of the comparator unit (the input of the square-cfc extraction unit) and the temperature of 35 (Tj requires that Uj be associated with

and

TO

and

6W

(2)

40

A power amplifier, 9 is necessary to amplify the signal from the output of block 7 to a level sufficient to operate the heater, and can be made as a voltage follower with current gain (i.e., in general, power). Since the resistance of the heater must be constant in time and independent of temperature, blocks 8

 To 9 can be combined, and then the circuit of the negative feedback can be made in the form of a square root extraction unit with an output power amplifier,

55 covered by local negative feedback, one of the options for the implementation of which is shown in FIG. 3

k. R "

- t

  - №

(one)

Where

k - coefficient of proportionality j

UH and Rj, are respectively the voltage across the heater and its resistance.

thirty

To obtain a linear relationship between the output voltage of the device generated at the output of the comparator unit (the input of the square-cfc extraction unit) and the temperature of 35 (Tj requires that Uj be associated with

and

6W

(2)

A power amplifier, 9 is necessary to amplify the signal from the output of block 7 to a level sufficient to operate the heater, and can be made as a voltage follower with current gain (i.e., in general, power). Since the resistance of the heater must be constant in time and independent of temperature, blocks 8

To 9 can be combined, and then the circuit of the negative feedback can be made in the form of a square root extraction unit with an output power amplifier,

covered by local negative feedback, one embodiment of which is shown in FIG. 3

The square root extraction unit (Fig. 3) contains resistors 10 and 11, the ratio of which specifies the value of the coefficient k, the operational amplifier 12, the gain factor of which at. open-loop feedback tends to infinity-, power amplifier 13 and quad 14, the power amplifier can be implemented on transistors according to the scheme of a push-pull power amplifier operating in the emitter follower mode.

Since the heat flux sensor performs the role of zero indicator of heat flux- (equality of temperature gradient on both sides of the sensitive element of the heat flux sensor), the instability of its parameters does not affect the measurement error. Sensitivity of the heat flux sensor to the gradient temperature difference can reach hundredths of a degree, the drift of the equivalent bias voltage of modern DC amplifiers is tenths of a microvolt; even if the output emf of a sensitive element of the sensor is several millivolts, it is the instability of the resistance of the heaters when used to create them manganin or constantan reaches hundredths of a percent when changing

heater temperatures of a hundred degrees, i.e. the resultant error of the device may be less than 0.1% for a wide range of measurements of positive temperatures. The error of heat dissipation into the space surrounding the sensor can be neglected, since with this design of the heat flow sensor, the edge effects are insignificant.

The negligence of the change in the gain of amplifier 5 is also negligible, since it is covered by deep negative feedback through elements 6, 8, and 9.

The error of the square-root extraction unit 8 may be insignificant at sufficiently high levels of the output signal of the amplifier 5 and when this is realized

devices according to the scheme shown in FIG. 3, the error in the ratio of the resistors 11 and 10, which may be negligibly small (hundredths of a percent), and the quad error, which may be less than 0.1%, are determined.

3

and wyk

Utm

Uh

Compiled by V. Kulikov Editor 0. Kolesnikova Tehred I.Astalosh Corrector V. Sinitska

Order 8517 / 42Tirizh 896 Subscription

VNIIPI USSR State Committee

for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5

Branch PPP Patent, Uzhgorod, st. Project, 4

eleven

t

Claims (1)

TEMPERATURE MEASUREMENT DEVICE, comprising a heat flux sensor with a heater in contact with a heat flux sensor sensing element connected to an amplifier input, a power amplifier, the output of which is connected to a heater, characterized in that, in order to increase the measurement accuracy, a square root extraction unit, a reference voltage source, and a comparison unit, the inputs of which are respectively connected to the outputs of the amplifier and the reference voltage source, are introduced into it; exit through the square root extraction unit - with the input of the power amplifier