SU682772A1 - Apparatus for measuring flux of radiation energy - Google Patents

Description

The device relates to the field of radiation pyrometry and can be used to measure radiant energy fluxes, in particular, to measure the temperature of heated objects from radiation.

Devices are known for measuring the flow of radiant energy by converting it into an electrical signal and measuring the magnitude of this signal. These include thermoelements, bolometers, optoacoustic receivers, zaporographic transducers, dielectric mono-electrical receivers and other thermal transducers. Widespread devices based on thermoelements. In these devices, the radiant flux incident on the receiving platform and absorbed in it increases the temperature of the sensing element, which is a thermocouple or thermopile of several thermocouples connected in series, resulting in a thermo-emf that is proportional to the radiative progeny, which is then measured. The magnitude of the temperature increase of the thermal element temperature depends both on the magnitude of the flux of radiant energy and on the intensity of thermal emission to the environment along the branches of the thermoelement due to radiation and convection.

To increase the sensitivity of such devices, they tend to reduce heat transfer, which in turn leads to a decrease in speed. Such a relationship of sensitivity and speed is due to the fact that the registration of the thermal emf is made after the heating of the spa and the branches of the thermoelement, and the duration of the heating increases with a decrease in the intensity of heat exchange with the environment.

The closest in technical essence to the proposed device is a device for measuring the flow of radiant energy, consisting of a series-connected thermoelectric radiation receiver, amplifier and measuring instrument.

In this device, an increase in speed is achieved due to the fact that a current causing the Peltier effect is passed through the junction of the thermocouple, and the magnitude of this current is proportional to the incident energy flow. As a result, the degree of heating of this sensitive element and the time it takes to establish the steady state state is reduced.

The disadvantage of such a device is that the increase in speed is accompanied by a decrease in the sensitivity or resolution of the system.

radiation registers, which is determined; the magnitude | Other signal-to-noise ratio. This is due to the fact that in this device you reduce the degree of heating of the thermopesha and the signal at the input of the amplifier compared to the heating and signal without feedback, and the system noise (with a relatively small flow of radiant energy) ), the value of which is defined as

V:;, 1/4 / gG / L /,

where k is the Boltzmann constant;

T -. temperature; ° K;

R is the resistance; D / is the bandwidth of the amplifier, remain almost unchanged. In this way, the signal-to-noise ratio is reduced, and, therefore, resolvable, and the ability of the radiant energy recording system.

The aim of the invention is to increase the speed of the movement. This goal is achieved in that a phase-sensitive executive mechanism and a current generator are injected into the device for measuring the flow of radiant energy, the phase-sensitive actuator input is connected to the amplifier output, the current generator output is connected to the thermoelectric radiation receiver, and the measuring device is on to the output circuit of the current generator. The imp is given a block diagram of the proposed device.

The device (see schelt) consists of a series-connected thermoelectric receiver / radiation unit, amplifier 2, phase-sensitive actuator S, current generator 4, and measuring device 5.

The device works as follows.

The incident radiant energy flux q causes the receiving site lag and the appearance at the receiver / signal output. As soon as the magnitude of this signal, amplified by amplifier 2, exceeds the threshold value (noise level), a phase-sensitive mechanism 5 is triggered, controlling the current generator 4, from its output a current is passed through the thermoelectric receiver but increases in time. that, it causes the Peltier effect on the junction of the thermal receiver, and thereby reduced the temperature of the junctions and the receiving platform. When the power absorbed by the Peltier effect, defined as P / aG (/ is the current magnitude and the thermo-emf coefficient, G is the temperature ° K), reaches a value equal to the incident flux q, the signal at the amplifier's input becomes equal zero, and the phase-sensitive executive mechanism provides a constant current value at the output of the current generator. As the incident flux decreases, the power absorbed by the Peltier effect begins to exceed q, the receiver junction cools, a negative polarity signal appears at the input and output of the amplifier, the phase-sensitive actuator causes the output current to decrease from the current generator until Peltier does not compare with the falling density. About the magnitude of the incident flow

according to the indications of the measuring device 5, which records the amount of current flowing through the thermoelectric receiver, which is proportional to the magnitude of the incident flow.

The device does not decrease sensitivity due to the fact that negative feedback is turned on when the temperature of the system reaches the threshold of sensitivity, and

a phase-sensitive actuator permits 100% negative feedback.

To separate the useful signal thermo-EMF Ea. from the potential difference arising as a result of the transmission of the compensating current / through the sensing element and in order to avoid shunting the input of the amplifier by the generator output then.

included in one of the shoulders of a balanced bridge.

The theoretical calculation shows that the spa temperature of the sensitive element of a thermoelectric receiver when the radiant flux q falls on the beam and the absence of a current is determined by the formula

/ zP

ert

(V)

c-jS

e а - coefficient of heat exchange with the environment;

X is the coefficient of thermal conductivity of the branches of the thermoelement;

5 - cross-sectional area of the branches;

R is the perimeter of the branches;

c — specific heat capacity;

7 - density;

t is time;

at

9o

(2)

C a: s5Ya

Claims (1)

65 thus 7 - 7 „erf If the sensitivity threshold of the system is A7, then the time after which the compensating TO.CON G will be switched on - iTgjS 4 Гр Time T2, for which the temperature of the sensitive element's temperature will return to the initial one after switching on the compensating current linearly increasing at a rate p, is determined by the expression. Thus, the time, the response of the feedback system, t, is composed of the time Tb during which the junction heats up to the threshold temperature that triggers the feedback system, and T2, for which Your spa temperature will return to its original level. Time T2, as can be seen from expression (5), is determined only by the rate of rise of the compensating current p and can be obtained by using a sufficiently small application of the appropriate feedback system. Let us compare the reaction time of the system with feedback g T1 + T2 with the time taken to establish the temperature of the receiver for feedback without feedback. Let us take the resolving power of the recording part, equal to AG, relative measurement error k - „- at 0.1. t From expression (6) it can be seen that at a sufficiently high rate of rise of the compensating current p and low heat transfer to the environment, the speed of the feedback system is more than a hundred times higher than the speed of the system without feedback. When a compensating current passes through a thermoelement, besides the Peltier effect, the Joule heat is generated in the junction in the volume of its branches on the ohmic resistance, which leads to a deviation from the linear dependence of the power absorbed at the junction on the current magnitude and the occurrence of an error. However, in conventional radiation receivers, in which the most promising semiconductor materials with high thermoelectric efficiency are used, due to the incident flux, the spa of the receiver and its branches are heated, causing a change in the basic parameters of the thermoelement: thermal emf a, thermal conductivity x and electrical conductivity a, which leads to a deviation of the output signal from the linear. With a large incident power, the heating reaches a very significant value, and even the thermal destruction of the radiation receiver occurs. The calculation on the computer and experimental verification showed that the thermoelectric receiver used without a thermal feedback system has much worse linearity and greater error, especially in the area of high power compared to the proposed device, which does not heat the spa as a result of applying the Peltier effect. Thus, the transmission of the compensating current / allows not only to increase the speed and improve the linearity, but also to expand the range of the recorded powers by more than an order of magnitude while maintaining the measurement accuracy within 10%. Apparatus for measuring radiant energy flux, consisting of a series-connected thermoelectric radiation detector, amplifier, and measuring device, characterized in that, in order to improve speed, a phase-sensitive actuator and a current generator are inserted into it, while the phase-sensitive input an actuator is connected to the output of the amplifier, the output of the current generator is connected to a thermoelectric radiation detector, and the measuring The instrument is included in the output of the current generator circuit.