SU953471A1 - Low temperature digital meter - Google Patents

Description

(54) -DIGITAL LOW TEMPERATURE METER

one

The invention relates to temperature measurements, namely, devices for measuring low temperatures with automatic compensation of the thermoelectric power of the free ends of a thermoelectric thermometer.

Methods and devices are known to compensate for the change in thermo-EMF of a thermoelectric thermometer when the temperature of its free ends changes, for example, by taking into account the temperature correction of the free ends, by thermostating the free ends using passive or active thermostats and extension thermoelectrode wires - J3.

However, the known methods and devices have significant drawbacks. When taking into account the amendment to the {measurement result, it is necessary to measure the temperature of the free ends and, using the calibration characteristic of a thermoelectric thermometer, by calculation

Measure the measurement result. This method is difficult to automate and requires measuring the temperature of the free ends,

Also known devices gage com-. a CT sensor thermometer for automatic compensation of changes in the thermo-emf of the TT, which are an equal-shoulder bridge, whose three arms are made of manganin wire,

10 and the fourth - from copper. The bridge is powered by a stabilized voltage source and the output is included in the gap between the CT output and the secondary meter input.

The inclusion of a compensation device at the device input significantly impairs the measurement immunity, and in addition, various modifications of the CT

20 have low accuracy. The error in compensating for the change in thermo-emf CT in the range of temperature changes of the free ends O-50 C is below ± 3 C. The closest in technical cyuuiocTvi and the achieved result to the proposed digital temperature meter is a temperature measuring device containing a thermal electric thermometer and successively connected amplifier , a resistor, a switch, an integrator, a comparison device and a selector, to the second input of which the output of the generator is connected to such impulses, the input of which is connected to the output the automatic frequency control device, the second input of the comparator device is connected to the common bus, a digital reading device, a control unit and a piecewise linear approximation unit, the output of which is connected to one of the fixed-contacts of the switch and the input of the integrator, is connected to another fixed contact of the switch The signal inputs of the control unit are connected to the input of the automatic frequency control device and the output of the clock generator, a. the outputs are connected to the control inputs of the switch unit. Piecewise linear approximation, selector and digital counting device 5. The disadvantage of this device is the lack of automatic compensation for changes in the temperature of free TT pipes, and the use of any of the described methods and compensation devices does not provide sufficient accuracy. The purpose of the invention is to increase the accuracy of temperature measurements. The goal is achieved by introducing a reversible counter into the device, a second piecewise linear approximation unit, a key, a thermistor, and a resistance to voltage converter, to the input of which a thermistor is connected via a four-wire communication line, and the output is connected to one of the fixed contacts of the key, another fixed contact is connected to the output of the thermoelectric thermometer, and the moving contact is connected to the amplifier input, the output of the second piecewise linear approximation unit is connected to the common connection point the necessary contact will switch (the output of the first block of piecewise-pineway approximation and the integrator input, the summing and subtracting inputs of the reversible counter are connected to the corresponding selector outputs, and the outputs are connected to the inputs of the digital reading device, and up to 714 the control outputs of the control unit are connected to The secondary inputs of the second block are piecewise linear approximation and key, and the signal inputs are with the output of the comparator and a reversible counter. FIG. 1 shows a diagram of a digital meter, low temperatures; in fig. 2 (a, b) - graphs explaining the operation of the device, The device contains a thermoelectric thermometer 1, switch 2, amplifier 3. resistor 4, switch 5, integrator 6, comparing device 7, selector: torus 8, digital reading device 9 , the first block 10 piecewise linear approximation, the device 11 automatic frequency control, generator 12 clock pulses, reversing, counter 1 3 pulses, thermistor 14, resistance converter 15 to voltage, second block 16 piecewise linear approximation, block 17 control. Digital low temperature meter (Fig. 1) contains a series-connected thermoelectric thermometer 1, key 2, amplifier 3, resistor 4, switch 5, integrator 6, comparing device 7, and selector 8, to the second input of the selector 8 connected to the generator output 12 clock pulses , and the corresponding outputs of the selector are connected to the summation and subtractive inputs of the reversible counter 13 pulses, the outputs of which are connected to the inputs of the digital reading device 9, as well as the device 11 of automatic frequency control,. the output of which is connected to the generator input 12 clock pulses, the first 1O and the second 16 blocks of piecewise linear approximation, the outputs of which are connected and connected, to the common connection point of the fixed contacts of switch 5 and integrator input 6. Thermistor 14 using a four-wire. The communication lines are connected to the input of the resistance-to-voltage converter 15, the output of which is connected to one of the fixed contacts of the key 2. The signal control unit 17 is connected to the output. the comparison device 7, the input of the automatic frequency control device 11 and the output of the reversible counter 13 pulses, and the outputs with control inputs of the key 2, the switch 5, the selector 8, the digital reading device 9, the 12 clock pulse generator and blocks 10 and 16 of the linear linear approximation . The device works as follows. When the device is turned on, the signals from the control unit 17 switch the key 2 to the lower position, corresponding to connecting the output of the resistance converter 15 to the voltage input of the amplifier 3, switch 5 to the upper position, which corresponds to connecting the resistor 4 to the integrator input b, and The outputs of the 10 and 16 pieces of the linear-linear approximation are disconnected from the input of the integrator 6, the outputs of the selector 8 are disconnected from the inputs of the reversible pulse counter 13. At the same time, the input of the integrator 6 is equal to (1) -eff.;) nt y Strength of amplification K l 3; - voltage at the output of the converter 15 resistance to voltage, the value of which is equal to bs. - Coefficient of resistance to voltage converter 15; the increment of the resistance of the thermal resistor 14 e by changing the temperature 9 eV. whose value is equal to ARft. (initial displacement Uoi; g l n o ° ® is synthesized by any known method); where RO is the resistance of the thermistor 14 at O ° C; on - temperature coefficient of resistance of resistor 14; © temperature of free ends of thermoelectric thermometer 1, since thermistor 14 is located in close proximity: from free ends of thermoelectric thermometer 1 and thus is at the same temperature 0 (-. g, as free ends. The voltage U is integrated by the integrator 6 during the time interval T, the duration of which is chosen equal to the period of the supply voltage of the device’s power supply and is set by the control unit. At the end of the interval T the output the integrator, a voltage arises ... where (is the resistance of the resistor 4; C is the feedback capacity of the integrator 6. After the interval T has expired, the signals from the control unit move switch 5 to the lower position corresponding to the common bus connection, the output of the second block 16 is piecewise linear approximation is connected to the integrator input .. 6, and the output of the selector 8 is connected to the subtractive input of the reversible counter 13 pulses for passing pulses from the generator 12 clock pulses, the voltage from the output of the second block 16 is piecewise-linear This approximation is integrated during the time i / x, until the moment until integrator 6 returns to its original state, i.e., until the equality rUo-t cdvsv cP d; : (5) is the voltage of opposite polarity to U, which through discharge resistors R (0 (-g) of the second block 16 of the piecewise linear approximation discharges the integrator to zero (Fig. 2, a). Thus, the interval time is determined by equating (4) and (5), whence K-T-Tsbsv-Dbsv) uTi where CD) St) is the discharge resistance of block 16 of linear linear approximation, which works similarly to the piecewise linear approximation block of the known device. The moment of lambing of the interval t, i.e. the return of the integrator to the initial state, is fixed by a comparison device 7, the output of which control unit 17 controls its own and sipnals switches key 2 to the upper section corresponding to the switch of thermoelectric thermometer 1 to the input of amplifier 3, switch 5 goes to the upper position, connecting resistor 4 to the input of the integrator 6, the output of the second block 16 piecewise linear approximation disconnects from the input of the integrator, and the selector 8 closes, and the passage of pulses from the generator Pa clock pulses 12 to the subtractive input of the reversible pulse counting 13 is interrupted. In the reversible counter, the code of the number N.iot is stored, where {Q is the pulse frequency or pulse of the clock pulse generator 12. At the end of the interval, after appropriate switchings, the amplifier .3 output terminal of the thermoelectric thermometer is applied to the input of the integrator 6 1, the value of which is equal to (0 „св св), is the gain of the amplifier 3; (bhbsv) output Tepvio-EMF of a thermoelectric thermometer 1 9 X - measured temperature; Qpj is the temperature of the free end. Value of Е (0 х, 0 се). But imagine E (ex, bsv) E (bx, 0C) DE (o ° C, Sun), (9) where, О С) - thermo - EMF corresponding to the values at which the instrument is calibrated; LU (О ° С, QCB correction to thermoelectric thermopower thermometer 1 with the temperature of the free ends © ce, and ® X (digital low temperature meter) and Q se Oc (which always takes place during operation of the device). At these times, the voltage is always E (bh, 0sv) E.. ®) and the relation (9) is always fulfilled. The voltage Uj is integrated by the integrator 6 (as in the previous case vJ) during the time interval T, the duration of which is set by the control unit 17 by allocating an interference period (the period of the instrument supply voltage). At the end of the interval T, at the output of the integrator, a voltage of П-III А i QxQcB occurs) or taking into account (9) p (Q o ° cl -T-uE (o ° c, ecBi ,, i - г :: +. I RCRC After the interval T has expired, the control unit 5 switches the switch 5 to the close position corresponding to the common connection, the selector 8 opens 12 clocks for the pulse from the generator 12 clock pulses to the summing input of the reversible counter 1 Parameters and connects the integrator to the input of the integrator. the resistor R of the block 0 is a piecewise linear approximation of the voltage opposite to the polarity of IC, At the end of this interval, the detector transmits 13 pulses through a zero reversing meter, the output of which the control unit connects to the input of the integrator a voltage and through through the discharge the resistors hs (bh) of the 1D block is piecewise linear approximation and the integrator discharges for a time t to its initial state until the equality J Uodi) C (11) RjC where Cs (O) is the value of the discharge resistances of the block 10 piecewise linear approximation which It works similarly to the piecewise linear approximation block of a known device. The time interval b will be defined by equating (10) and (11), that is, KT-E (Qx, 0 ° C) KJ-uE (0 ° C, 8cB) R.OxVc wx KT-Eie, OOc Uot R3lQx) -c (12) KTuE (0 ° C. ecBl UoRC RJC from expression (12), we define a time interval whose value is kt.E (bMO ° c.rs (ex)). To obtain a linear dependence of the time interval 1- of the measured temperature 9 X, it is necessary to ensure i, the condition E (ek, 0 ° C) -Naz (9k) ,,,.) since the remaining values of K, T, Kg and R in equation 14 are constant. 15 it is necessary that R (SX) have an inverse functional dependence E (0 x,), which is accomplished by block 10 piece; 1 is a non-linear approximation - 4l rake of resistance values of RIB depending on the measured temperature 8d approximate the expression E (0y, O ° C) piecewise pin-dependence and then calculate the values) To obtain a condition that compensates for the temperature of the free ends, we substitute the value t in (13) from expression (b). Thus, we obtain .Uec8-f 0cB) uElO ° c, the condition is both prepared by the fact that UQ Ri (9ce) has the same functional dependency 1m as ЕE (, Ee (}), which is provided by the second block 16 piecewise-linear approximation. resistances R (.9cg) are calculated as in a known device, after having approximated the expression ЕЕ (, QC) by a piecewise linear dependence, based on the necessary accuracy of compensation for changes in the temperature of the free ends of a thermoelectric thermometer 1. The dependencies Е (0х) and Д Е ( .O ° C, 9f4gi) are given by the thermoelectric calibration characteristic of the electric thermometer. ,, -At the moment the interval -o ends, the control unit transmits the receiver units to the initial state by a signal of the comparator 7 and the measurement cycle repeats at the end of the time interval t. N2 iot3 Qx, - o Thus, in the proposed low-temperature digital meter, by additionally inserting a key, a thermistor, a resistance converter to voltage, a second block of piecewise linear approximation, a reversible counter, and boiling bonds zna-- considerably povyschaets temperature measurement accuracy, to provide automatic compensation effect of temperature change of the free ends of the thermoelectric thermometer on the measurement result. In the proposed device, the accuracy of compensation for changes in the temperature of the free ends is increased more than an order of magnitude due to the high precision of the piecewise linear a7 triaxing of the scraper. (C (. 0; -z) and the corresponding output produced by the second block 1 1 of the linear-linear asproximer 1shi zapisimogti LOSv) The invention Invention A digital low-temperature meter containing a thermoelectric thermometer and a series-connected device, resistor, and integrator, comparing device and A selector, to the BTopt Mu whose input is connected to the output of a clock pulse generator, whose input is connected to the output of an automatic frequency control device, and the second input of the comparison device is connected to a common bus, a digital output The metering device, the control unit and the piecewise linear approximation unit, the output of which is connected to the common connection point of one of the fixed contacts of the switch and the integrator input, is connected to the other fixed contact of the switch, and the signal inputs of the control unit are connected to the input of the automatic frequency control device and the clock generator output, and the outputs are connected to the control inputs of the switch of the piecewise linear approximation block, the selector, and the digital readout A device, characterized in that, in order to improve the temperature measurement accuracy, a reversible pulse counter, a second piecewise linear approximation unit, a key, a thermoresistor and a resistance converter into a voltage, the input of which is connected via a four-wire communication line, are inserted into it, and the output is connected to one of the fixed contacts of the key, the other fixed contact of which is connected with the output of the thermoelectric thermometer, and the movable contact is connected to the input of the amplifier, the output of the second block is piecewise -linear approximation is associated with a common point compound nepodvgoknogo contact switch output of the first block piecewise linear approximation 1matsii and input m-gtegratora, summing and subtracting inputs of the reversible counter ikshulsov. connected to the corresponding outputs of the selector. and the outputs are connected to the inputs of the digital reading device, and the additional outputs are controlled by the control inputs of the second block piece-pinned appr cnr-ralriT and lUiV.- ,. .TLP.-IC. With PHOL1. - with the output of the device and reversible pulse counter. Sources of information taken into account in the examination 1. Preobrazhensky V. P. Thermal engineering measurements and devices. M., Energie, 1978. p., 95. L471. 2. In the same place 119. 3. In the same place, p. 116 4.The same, p. 121. 55. USSR Author's Certificate for Application No. 2787095/1 8-1О, cl. Q 01 K 7 / O2, 07.07.79 (prototype).

Claims (1)

Claim A digital low-temperature meter containing a thermoelectric thermometer and a series-connected amplifier, resistor, integrator, comparator and selector, to the second input of which the output of the clock generator is connected, the input of which is connected to the output of the automatic frequency control device, and the second input of the comparative device is connected with a common bus, a digital reading device, a control unit and a piecewise linear approximation unit, the output of which is connected to a common connection point of one of the the fixed contacts of the switch and the integrator input, a common bus is connected to the other fixed contact of the switch, the signal inputs of the control unit connected to the input of the automatic frequency control device and the output of the clock generator, and the outputs connected to the control inputs of the switch block piecewise linear approximation, selector and digital reading device, characterized in that. that, in order to improve the accuracy of temperature measurement, a reversible pulse counter, a second piece of piecewise linear approximation, a key, a thermoresistor, and a resistance to voltage converter are introduced into it, to the input of which a thermistor is connected via a four-wire communication line, and the output is connected to one of the fixed contacts a key, another fixed contact of which is connected to the output of the thermoelectric thermometer, and a movable contact is connected to the input of the amplifier, the output of the second block of piecewise linear approximation is connected n with a common point of connection of the fixed contact of the output switch of the first block of piecewise linear approximation and the input of the integrator, summing and subtracting the inputs of the reversible pulse counter are connected to the corresponding outputs of the selector. and the outputs are connected to the inputs of the digital reading device, and the additional outputs of the control unit are connected to the control inputs of the second block piecewise linear simappro! and key. h. γγγιι. · ι.ίμιιle entrances - 953471. 1 2 with the output of the comparison device and the reversible pulse counter.