SU958875A1 - Device for measuring temperature - Google Patents

Description

(54) DEVICE FOR TEMPERATURE MEASUREMENT

one

The invention relates to temperature measurements, namely to temperature measuring devices, in which a thermosensitive logarithmic diode is used as a sensitive element.

A device for temperature measurement is known, which contains a transistor temperature-sensitive element included in the bridge measuring circuit 1.

The drawback of the device is a large variation in voltages at the direct displaced emitter junction among different transistor instances, which limits their interchangeability and leads to low measurement accuracy even with individual sorting into groups with similar parameters.

The closest to the proposed technical essence and the achieved result is a device for temperature measurement, containing two current sources with analogue keys and a heat-sensitive semiconductor diode, connected to the logarithm, whose input is connected to the current sources 2 through analogue keys.

The disadvantage of the device is that a part of the output voltage is determined by the volume resistance of the diode, the spread of which is significant in various instances of even diodes of the same type. This reduces the measurement accuracy and limits the interchangeability of thermosensitive diodes.

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

The goal is achieved by introducing a reversible integrator, a time interval adjuster, a comparator, a third current source with an analog switch, a voltage source, and an analog switch connected to the integrator's measuring input, the output of which through the comparator is connected to the input of the time interval setter 2Q. the first three outputs of which are connected to the control inputs of the corresponding keys, the fourth to the control input of the switch, and the fifth to the integrator control input, with The third source of current is connected via an analog switch to the input of the logarithm and the source of the reference voltage to the first input of the switch, the second input of which is connected to the output of the logarithm.

FIG. 1 is a functional diagram of a device for measuring temperature; in fig. 2 - timing diagrams illustrating the operation of the device.

The device for temperature measurement contains current sources 1, 2 and 3, analog switches 4, 5 and 6, logarithm 7 with a temperature-sensitive logarithm diode 8, reversible integrator 9, time interval setting unit 10, reference voltage source 11, analog switch 12 and comparator 13 The current sources 1, 2 and 3 are connected via analog switches 4, 5 and 6 to the current logarithm 7, the circuit of which includes a diode 8. Either the output of the logarithm 7 can be connected to the integrator 9 through the switch 12, or the reference voltage source 11. Integrato output 9 is connected to the input of the comparator 13, the output of which is connected to the input of the setting device 10, the first three outputs of the setting device control keys 4, 5 and 6, the fourth output controls the switch 12, and the fifth output - the integrator 9. The output signal of the temperature measuring device is removed from the output of the master timers 10.

The temperature measuring device operates as follows.

At the moment of time preceding the initial one, the integrator 9 was reset, and the keys 4, 5 and 6 are open. At the initial moment of time, the setpoint 10 receives signals for closing the key 4 and switching the integrator 9 into the direct integration mode. Current 1 | from the source of current 1 is fed to the input of the current logarithm 7. When current passes through diode 8, a voltage appears on it

 ,,

where K is the Boltzmann constant;

q. - elemental charge;

0 is absolute temperature;

Is is the characteristic current of the diode;

RO-volume diode resistance.

This voltage is applied from the output of the logarithm 7 to the integrator 9, at which it integrates during the time interval T. By the end of this interval, the voltage on the integrator is

Um. lQlni + RoI ,, where T is the integrator time constant.

At time 1 from setpoint 10, a signal is received to turn off key 4 and turn on key 5. Input I of current logarithm 7 receives current Ij from current source 2. The voltage L that occurs at output of logarithmator 7 is integrated during the time interval from it to t. 2u. At time 21, the voltage on the integrator is

si elnJf + Ro (I, + l2) f.

At time t 2Tno, signals from the setter, 10, open the key 5, close the key 6, and reverse - switch the integration direction of the reverse integrator 9. The input of the logarithm 7 from the source 3 receives the current Ij. The voltage Uj arising at the output of the logarithm is integrated by the integrator 9 during the time interval 2t from the time 1 2T to the time t 4t.

By the end of this interval, the voltage on the reverse integrator 9 is equal to

  f elni, + Ro (I, + l2-2l3) t (1) From expression (1) it is seen that if the condition

11-M2-2Ts 0,. . (2)

then the output voltage of the device

UH. (3)

directly proportional to the absolute temperature of the diode and does not depend on its specific volume resistance.

At time t 4t, the signal from the setpoint 10 switch 12 connects the input of the integrator to the source of the reference voltage 11, the output of the setpoint 10, which is the output of the device, is the logical signal "1. At the same time, the voltage at the output of the integrator decreases to zero during the time interval At, which can be determined from the equality

1 / w-M 0 (4)

where is the reference voltage.

After a time interval determined by equality, a pulse is formed at the output of the comparator 13, which initiates the beginning of a new time cycle, and the signal of a logical zero appears at the output of the setting device 10, which is the output of the device.

From a comparison of expressions (1) and (4) with regard to (2), it is possible to determine the relationship of the output time interval with temperature

.ein-4-,

The output signal in the form of the time interval A t is directly proportional to the absolute temperature and does not depend on the volume resistance of the temperature-sensitive diode and on the integration time parameters of the reverse integrator.

If necessary, the amplitude value of the output voltage of the reverse integrator, defined by expression (3), can be used to indicate the temperature.

In the proposed device, a high temperature measurement accuracy is achieved, which, in combination with a temporary output, makes it possible to use it in digital instrumentation.

Claims (2)

Invention Formula A temperature measuring device containing two current sources with analog switches and a thermo-sensitive semiconductor diode connected to a logarithm, whose input is connected to current sources through analog switches with current sources, in order to improve the accuracy of measurement, a reverse integrator is introduced into the device time intervals, comparator, third current source with analog key, voltage source and analog switch connected to the integrator's measurement input, output which is connected via a comparator to the input of the setpoint generator, the first three outputs of which are connected to the control inputs of the corresponding keys, the fourth to the control input of the switch, and the fifth to the integrator control input, while the third current source is connected to the input of the logarithmizer, and the source of the reference voltage to the first input of the switch, the second input of which is connected to the output of the logarithm. Sources of information taken into account in the examination of 1 USSR Author's Certificate No. 361398, cl. G 01 K 7/22. 12.03.71. 2. US patent No. 3812717, cl. G 01 K 7/24, published. 05/28/74 (prototype).