SU1394069A1 - Method of checking resistance thermal converters - Google Patents

Abstract

This invention relates to industrial thermometry. The purpose of the invention is to improve the accuracy of calibration of resistance thermoconverters. In the device that implements the method, the output of the adder 11 is a signal, which represents a mixture of two signals. The first one is equal to the amplified useful signal of the thermal converter (t) 1, the second one is a mixture of statistically independent noises of amplifiers 5–8 and lead wires. The signal at the output of the adder 12 consists, respectively, of the increased voltage fluctuations of the thermal noise of the controlled T2 and the noise signal of the amplifiers 5-8 and of the supply wires, which is characterized by the same dispersion as the second component of the signal at the output of the adder 1. Signals from the outputs of the adders 11 and 12 are fed to the inputs of transducers 13 and 14, which accomplish quadratic detection of signals and their subsequent statistical smoothing. silt (/)

Description

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The invention relates to the field of industrial thermometry and can be used in the debugging calibration of resistance thermocouples (TC).

The purpose of the invention is to improve the accuracy of calibration of resistance thermocouples.

The essence of the method is as follows.

The time constants of the measurement channels of the signals arriving at the input of the measuring device from the test and counterpart vehicle are written. Here, the resistances of the latter are measured, the values of C or Co are measured and equality is reached. Then the levels of thermal electrical fluctuations are measured, for example, using two quadratic voltmeters. From the well-known Nyquist formula it follows that in the absence of interference in the frequency range Af-fi-f measured mean square U thermal electric fluctuations

JU 4K JrJR (f) af, (1)

it,

where K is the Boltzmann constant; R (t) is the active component of the resistance that generates thermal electrical fluctuations at temperature T. The active component of the resistance of the thermal converter, at the terminals of which Thermal electrical fluctuations at the frequency f are measured, is equal to

R

 TTT o JSTi

T + r23iTRC7

(2)

where R is the resistance of the thermocouple;

С is the value of capacitance bypassing the resistance of the thermocouple.

The average value of the square of the voltage GC thermal electrical fluctuations of the control thermocouple in the frequency band dG at temperature T

 2TfR, CJj (3)

The average value of the square of the voltage Ufl of the thermal electric fluctuations of the thermal converter being tested in the dG frequency band at the temperature TC

iz

- Z 7KT GT Tj

U ".g - arctg, (4).

Measure the difference between the mean squares of the di-thermal electric fluctuations of the point and control thermocouples

AU - (arctg 27rf R Co-arctg 2Jf

rlu i. (5)

LC. C.

After measuring the difference of average squares AU, the actual value of calibration temperature T is determined from the ratio

20

t, t, ž (-.,).

(6)

Determining T and measuring B, build a calibration characteristic R

f (Ty,) of the calibrated vehicle, which makes it possible to amend its calibration characteristic. If there is interference, the average square of the interference voltage is summed with the average value of the square of the measured thermal noise voltage. As a result of subtraction, the voltage of the measured value of the difference of the average squares of thermal electrical fluctuations is eliminated.

The drawing shows a diagram of an apparatus for carrying out the proposed method of disassembling verification of tern-impedance transducers.

The diagram shows a testable thermoprotector 1 resistance, a control thermocouple 2 resistance, capacitance ZIL, amplifiers 5-8, inverting blocks 9 and 10,

linear adders 11 and 12, converters 13 and 14 are quadratic, subtractive unit 15, registering unit 16. The device works as follows.

The voltage fluctuations of thermal noise from the thermocoupler being turned 1, shunted with capacitance 3, are fed simultaneously to the inputs of the same amplifiers 5 and 6, and the voltage of the thermal noise from the control

thermal converters 2, shunted capacity 4, - to the inputs of the amplifiers 7 and 8. The adder 11 receives

noise signals from the outputs of amplifiers 5-7 and the signal from the inverter 10, the input of which receives a signal from the output of amplifier 8. Similarly, the adder 12 receives signals from the outputs of amplifiers 7, 8 and 5 and the signal from the output of inverter 9, to the input of which a signal from the output of amplifier 6. There is a signal at the output of adder 11, which is a mixture of two signals. The first is equal to the amplified useful signal of the thermal converter 1, and the second is a mixture of statistically independent noises of amplifiers 5-8 and supply wires. Due to the presence of the inverter 9, the corrected part of the signal at the outputs of the amplifiers 7 and B, due to the generation of noise from the control thermoconverter 2, is suppressed in the adder 11. The signal at the output of the adder 12 consists respectively of an increased voltage fluctuation of the thermal noise of the control thermoconverter 2 and the noise signal 5-8 and supply wires, which are characterized by the same dispersion as the second component of the signal at the output of the adder 11.

The signal from the outputs of the adders 11 and 12 is fed to the inputs of the blocks 13 and 14 conversion. Conversion units perform quadratic signal detection and their subsequent statistical smoothing. The output signals of the conversion units are fed to the inputs of the subtracting unit 15 and are recorded by the unit 16.

Claims (1)

Invention Formula The method of calibration of resistance thermocouples, including 10 20 25 4069 capacitance of the channel of the control thermocouple resistance, leveling the constant time of the channels of the control and calibrated resistance thermocouples, measuring the average squares of thermal electrical fluctuations of the control and calibrating resistance thermocouples and determining the temperature of the thermistor being converted, which differs from calibrations, measure the capacitance of the caiale of the thermocouple resistance being measured, and the difference x squares of their thermal electric. fluctuations, and the temperature of the thermometer being turned resistance is determined from the ratio t p  +1) s7iG 0 5 0 c 0 where TO is the set temperature of the control thermocouple resistance; the capacitance of the channel for measuring thermal electrical fluctuations of the thermoconverter under test; the capacitance of the channel for measuring the thermal electrical fluctuations of the control thermocouple; the difference of the mean squares of the levels of thermal electrical fluctuations of the calibrated and control thermocouples of resistance; mean square voltage thermal electrical fluctuations of the control thermocouple resistance. Cv, s -1 iU and.