SU898266A1 - Device for measuring temperature fields - Google Patents

Description

The invention relates to a measuring technique and can be used to measure the distribution and change of the scientific research institute of temperature in various media, such as in the soil, in studies of thermal processes in permafrost. Temperature measuring devices are known, the principle of action of which is based on measuring the change in resistance of pure metals with temperature and in which platinum thermometers 1 are most widely used. These devices have a wide range of operating temperatures, good linearity, but very expensive. Temperature measuring devices are known in which the temperature potential of the L.p - n junction is used as a function of temperature. Thus, the LX 5700 temperature sensor from National Semiconductor (USA) measures the difference in the AUpg base-emitter voltage of two matched transistors operating at different collector currents C and D for two ideally matched transistors having the same transition temperature, , permanently Boltzmann; - absolute temperature; - d d electron. From the above dependence it can be seen that the voltage 41 is linearly related to the temperature of the p – n junction. However, it is impossible to manufacture perfectly matched transistors. In addition, the change in the parameters of two diodes and transistors as a result of aging, even located on the same chip, occurs differently, which is another factor limiting the accuracy of these devices. This may explain the large long-term error of + 3.8 ° С in 30 days. The presence of thermal resistance between p-n junctions also increases the measurement error. Finally, the zero offset and temperature drift of subsequent amplifiers also reduces the measurement accuracy. The closest in technical essence and the achieved result to the invention is a device for measuring temperature, containing a source of reference voltage,. A scaling resistor connecting the voltage source with a diode and a DC amplifier connected to the diode, to the output of which the ST indicator is connected. The disadvantages of the proposed invention include the variation of the proportionality coefficient between temperature and voltage, reducing the accuracy of for offset zero and drif fa nu amplifier. In addition, this device can work only with one diode, since tuning is necessary when replacing a diode, very significant errors will occur due to the large scatter of the initial currents and volume resistances of the diodes. The aim of the invention is to improve the accuracy of temperature measurements. The goal is achieved by those that are in a temperature measuring device. fields containing an indicator, a diode unit whose outputs are connected to a switch connected to the preamplifier inputs, a pulse distributor, a controlled voltage converter, a selective amplifier, a phase-sensitive rectifier, a computing unit and a compensator, and the pulse distributor outputs are connected with the inputs of the computing unit, the compensator, with the control input of the phase-sensitive rectifier and with the inputs of the voltage-current converter, the outputs of the latter are connected to the inputs silicon, the output of which is connected to the first input of the selective amplifier, the output of which is connected to the phase-sensitive rectifier input connected to the input of the computing unit, the outputs of which are connected to the indicator input and the input of the compensator, which is connected to the second input of the selective input booster. In addition, the computing unit contains the first and second switches, the first and second integrators, and the subtracting unit, with the outputs of the first switch connected to the inputs of the first and second integrators, the outputs of which are connected to the inputs of the reading unit and the inputs of the second switch. The pulse distributor contains a generator, a reference voltage source, the first, second and third scale resistors, a switch and an amplifier, the output of the voltage source being connected to the first and second scale resistors, while the second end of one of the resistors is directly connected to the amplifier. and the other resistor through a switch whose control input is connected to the generator, and the third large-scale resistor is connected to the negative feedback circuit of the amplifier. The drawing shows a functional diagram of a device for measuring temperature fields. The device for measuring temperature fields contains a diode unit 1, a diode switch 2, a control voltage-current converter 3, a preamplifier, a selective amplifier 5, a phase-sensitive rectifier 6, a computing unit 7, a compensator 8, an indicator 9, a pulse distributor 10. The outputs of the unit the diodes 1 are connected to the inputs of the switch diodes 2, which by the outputs are connected to the outputs of the voltage-current converter 3 and to the inputs of the preamplifier k, the latter output is connected to the first input of the selective amplifier 5 to the output of which The signal input of the phase-sensitive rectifier 6 connected to the input of the computing unit, which outputs are connected to the indicator input and to the input of the compensator 8, is connected to the second input of the selective amplifier 5. The outputs of the pulse distributor 10 are connected to the inputs of the phase-sensitive rectifier 6 , the compensator 8, 58 of the computing unit 7, the controlled voltage-current converter 3. Computing unit 7 contains the first switch 11, the outputs connected to the inputs of the first 12 and second 13 integrators, the outputs of which are connected to the inputs of the second switch Tt and to the inputs of the subtracting unit 15. Pulse distributor 10 contains a generator 16 of the reference voltage source 17, to the output which connects the combined ends of the first and second large-scale resistors 18 and 19, the latter by the second end connected to the input of the switch 20, the output of which is connected to the input of the first amplifier 21, in the negative feedback circuit of which Added third scale resistor. Compensator 8 contains fourth, fifth, and sixth scale resistors 23-25. Second and third amplifiers 2b and 27, first and second field effect transistors 28 and 29, and capacitor 30 A device for measuring temperature fields operates as follows. The reference voltage of the voltage source 17 is fed to the input of the first amplifier 21 through the first scale resistor 18, and through the second scale resistor 19 and switch 20 connected in series to the control input of the switch 20 comes from the generator 16 output, the modulating signal Uc-f with frequency f. At the output of the amplifier 21, a pulsating voltage is formed with a frequency f, which is fed to the input of the controlled voltage-current converter 3. The slope of the converter 3 depends on the signal at the control input, to which the generator UcjB receives the modulating signal as a meander with the frequency f, which is much less than the frequency f. Thus, the converter 3 alternately takes two values of the conversion slope and a pulsating signal is generated at the output of the converter. current, whose ratio of maximum current to minimum, changing with frequency f, is constant, and the average value changes with frequency f, using a diode switch 2 controlled externally or by prog frame, the required diode is connected to the outputs of the voltage-current converter 3. The output 6 current which passage through the diode causes a corresponding drop on the p - junction of the diode. The variable component is amplified by a preamplifier, from the output of which is fed to the first input of the selective amplifier 5, to the second input of which is fed eg. The marriage from the output of the compensator 8, which is in antiphase and the difference between them, is amplified by a selective amplifier 5, the output of which is detected by the phase-sensitive rectifier 6. Depending on what value is greater (the signal from the preamplifier C or from the output of the compensator 8) the polarity of the signal is the output of the phase-sensitive rectifier varies, which passes through the first switch 11 to the input of the first or second integrator 12 and 13, depending on the magnitude of the control signal Ujj, causes a decrease or increase voltage at the output of the integrator. The output voltage of the integrator through the 2nd switch AND, switched synchronously with the first switch, is fed to the input of the second amplifier 26, causing a corresponding change in the gain ratio of the compensator, which reduces the difference signal amplified by the selective amplifier 5. This process goes on until the difference the signal will not become zero, i.e. until the voltages at the first and second inputs of the selective amplifier are compared. When the value of the control signal changes, the slope of the voltage-current converter 3 changes and the output of the phase-sensitive rectifier connects the input of another integrator, the output of which is connected by the second switch to the input of the second amplifier 2b, and the other integrator enters the storage mode, and the measurement process repeats at a frequency of fa. The voltages from the outputs of the integrators 12 and 13 are fed to the inputs of the subtracting unit 15, where the difference between the voltage at the output of the first integrator 12 and the scaled voltage of the second integrator 13 is determined, and the resulting difference goes to the indicator 9. A volmeter can be used as an indicator and / 1 and analog-to-digital converter with i-indication. At the output of the first amplifier, the voltage takes two values of 7 k K and Upp-Kg, where the K and the coGG transmit factors, the K-code K-20, are closed and open, respectively. The output current of the voltage converter 3 is 1 „, and 1 where S and S2 are the slopes of the converters controlled by the signal. The voltage on the diode Dd depends on the values of the controlled signals U takes four values: T cnKie.Rg ;. V M i..Ko J.ev,. ,, § Y 9 and - Lg aUonSa: 3о, where R. is the volume resistance of the diode. The variable component of the diode with the frequency f, amplified by the preamplifier C and fed to the first input of the selective amplifier 5, takes two values that change with the frequency f: (,) bUon, Rg-U2.-K,) Lyo-4- and ,,) to „-. eu, -. + Uon5iV i- l H where K is the transfer coefficient of the preamplifier In steady state, the voltage at the output of the compensator U0 is equal to the voltage at the output of the preamplifier, hence 01 and. . GH y 2-. The resistance of the channel of the first field-effect transistor 28 in the established mode, taking into account the fact that the polarity of voltage C, is opposite to the polarity of voltage U and Ug at the output of integrators 12 and 13 is equal to

Q

Kt

and,

about uon l ka-c-

thawing block 15 is equal to K, then its output voltage is and is equal to

s ik k and a

Og)

Taking into account (12), we get and.

Claims (3)

W - 6 - (-14) 8 When using 8 left transistors with identical parameters in the compensator, the coefficient of transfer of the kompatator 8 is equal to R 'R 5 5 SchG e R, Rg - and R - resistance of the fourth, fifth and sixth scale ",", „,. . x resistors 23 - 25. Substituting (4) into (5), we obtain y. Cdia., Won K - .M - oh. R6. the belt voltage at the output of the compressor 8 is equal to and - (k) -k, Jc), taking into account (6) and (7) (, H1, +); (a, a, (4) Equals in respectively (1) (8) (2), (9), we get U ,, - k,) U ,.). ° UonO 2-veK, - 0) - - Uon -aRg- i- tJ Multiply (11) by ft ,. 5 m from (10) and after transformations we get lJ.K5U4-- - | jU-) en.) If the scale factor in the calculation is Jl. And (l. / Lp., 2. b CV) ei, lJk-- on H-KgXKi-K -,) As can be seen from the expression (1), the output voltage Ugj ,, x is linearly related to the temperature p - n - junction and does not depend on the volume resistance of the diode and the initial current of the diode. If it is necessary to obtain a higher resolution when measuring small temperature fluctuations around the TCP temperature, then changing the K coefficient by replacing the fifth scale resistor, set the zero reference point to the mean value p. The following condition should be fulfilled: TCP K 6 UK It should be noted that this is of great importance when using the device as a multi-probe medical thermometer or when using it to measure thermal fields in permafrost when the temperature fluctuates around zero degrees. A significant advantage of the proposed The device is that the accuracy is practically determined by the spread of the passive elements. In addition, the scatter and variation in the results of aging, thermal current and volume resistance of the diodes, zero bias and amplifier drift do not affect the accuracy characteristics of the device. The economic effect is to increase the resolution and accuracy of the device. Claim 1. Device for measuring temperature fields, containing an indicator, a diode unit, the outputs of which are connected to a diode switch associated with the preamplifier inputs, characterized in that, to improve the accuracy of temperature measurement, a distributor of 8 6 O pulses is inserted into it, controlled voltage-current converter, the outputs of the latter are connected to the inputs of the preamplifier, the output of which is connected to the first input of the selective amplifier, to the output of which the input of the phase-sensitive rectifier is connected , Binding zannrgo output to the input of the computing unit, which are connected to the outputs of the input indicator and the input compensator, which output is coupled to the second input of the selective amplifier. 2. The device according to claim 1, wherein the computing unit contains the first and second switches, the first and second integrators and the subtracting unit, with the outputs of the first switch connected to the inputs of the first and second integrators, outputs which are connected to the inputs of the subtracting unit and the inputs of the second switch. 3. The device according to claim 1, wherein the pulse distributor comprises a generator, a reference voltage source, a first, second and third scale resistors, a switch and an amplifier, the output of the reference voltage source being connected to the first and second scale resistors , while the second end of one of the resistors is connected to the input {ol amplifier directly, and the other resistor via a switch, the control input of which is connected to the generator, and the third large-scale resistor is connected to the negative feedback circuit of the amplifier. Sources of information taken into account in the examination 1. The current state and trends in the development of measuring transducers of temperature into an electrical signal. - Express information. Testing and measuring technology, 1980, ff 1, pp.23-31. 2. Rizenman. Integral temperature sensors. - Electronics (translated from English) vol., No. 23, 1974, p. 57. 3. US Patent No. 3780585, cl. publish 1973 (prototype).