SU939964A1 - Device for automatic checking of thermocouple thermal inertia index value - Google Patents

Description

(5А) DEVICE FOR AUTOMATIC CONTROL OF THE VALUE OF THE INDICATOR OF THERMAL INERTIA OF THERMOPARS

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The device relates to electrical measuring equipment and is designed to automatically control the value of the thermal inertia index of thermocouples during acceptance tests in accordance with the requirements of GOST 6616-7.

The control of the dynamic properties of thermocouples according to the requirements of GOST is carried out by means of processing to oscillograms, on which their transient characteristics are recorded. Such control, especially in the conditions of mass production, is labor-intensive and in some cases does not provide the required accuracy.

Devices are known for measuring the time constant of thermal sensors, the basis of which is based on the method of recording the values of the output value. 20 spun thermocouples at a set of points in time on its transient response and automatic processing of these results using algorithms specified by the circuit implementation of the measuring equipment f 1}, 2} and fj.

However, these solutions have a common drawback - they are based on the fact that the thermocouple is a first order dynamic aperiodic link. In fact, thermocouples, especially those that have a cover welded with a sensitive element, under the test conditions provided for by GOST are described with sufficient accuracy only by an aperiodic link of no less than third order. Therefore, using thermocouples of known solutions for the purpose of automatic control of the thermal inertia index of thermocouples leads to significant methodological errors.

The closest in technical essence and the achieved result when used to the proposed is a device for measuring the thermal inertia index of thermocouples.

a heater, a measuring amplifier; a switch of the thermocouple signal; a switch; a storage element of the established value of a thermocouple signal; with a reset key; a large-scale amplifier; a three-pole analog switch; a resistive voltage divider; a comparison circuit; a trigger; a single vibrator;

In the process of measurement, the memory element captures the steady-state value of the output voltage of the thermocouple E, and the scale amplifier and resistive divider form the reference voltage E 1, 272Eo and E 1, 1 E 1)

For the exponential transitional characteristic of the first-order aperiodic link, the time constant T can be defined as ti - ti

T

h but

(2)

en

-k En

- one

where t

in which the values of voltages and E-2 are fixed on the transient characteristic of the thermocouple. In view of (1), equation (2) is converted to

T t, - t At (3) The time interval is measured and reported by the digital recorder as the value of the thermal inertia indicator j of the thermocouple.

However, the device is fully inherent in the methodological error of approximation of the exponential real transient characteristics of the thermocouple.

The purpose of the invention is. improving the accuracy of control over the value of the thermal inertia index of thermocouples.

The goal is achieved in that the device containing the measuring amplifier, whose input is connected to the thermocouple being tested, and the output through the switch key of the thermocouple signal channel with the storage element of the reset thermocouple signal key, resistive voltage divider, input the beginning of the regular mode, the automation unit, the storage elements of the intermediate values of the thermocouple signal with the reset keys, the subtractive. elements, comparators, two dvuhpoz and two three-position logical elements And and elements

signaling, while the inputs of all storage elements are connected via channel switch keys to the output of the measuring amplifier, the minus inputs of the subtracting elements are connected to the output of the first storage element of the intermediate thermocouple signal, at the start point of the regular mode the inputs of the remaining memory elements of the intermediate thermocouple signal the output of the last subtractive element is connected to a resistive voltage divider, and

The outputs of the remaining subtractive elements are connected to the first inputs of the comparators, the reference inputs of which are connected to the output of the resistive voltage divider, the outputs

Larger or Equal Comparators are connected respectively with the first

the inputs of the first two-position and three-part logic elements, And, and the outputs are Less connected to

the second three-position inputs and the first input of the second .sampling logic elements AND, the inputs of the threshold triggering and separation of the regular mode start are connected to the output of the measuring amplifier, the output of the threshold triggering unit is connected to the first control input. of the regular mode is connected to the second control input. Start of the automation unit, the first output of which is connected to the control inputs of the reset keys of the storage elements, the second and subsequent outputs Automation unit connected to the control inputs of the switch key channel, the last switch box output is also connected to second inputs of the two-position and three-position to third inputs of the AND gates, the outputs of AND gates are connected to the signaling elements, and automation unit is provided with a third input signal from the external control

0 Reset.

FIG. 1 shows a block diagram of the device; in fig. 2 - graphical transient characteristics of thermocouples.

Claims (3)

1. USSR author's certificate ff 300783, cl. G 01 K 7 / Y, 1971. 2. USSR author's certificate If 624123, cl. G 01 K 15/00, 1978. 3. Certificate of Certificate CCCf If 669227, cl. G 01 K 15/00, 1979. k. USSR author's certificate W 655912, cl. G 01 K 15/00, 1979 (prototype). 2yy Cffpoc