SU1242727A1 - Device for measuring temperature - Google Patents

Abstract

The invention relates to temperature measurements, namely, devices for measuring temperature using resistance thermal converters. The purpose of the invention is to improve the measurement accuracy. The device contains resistance thermocouple 1, comparison circuit 4, digital-to-analog converters (D / A converters) 5 and 6. Exemplary resistors 2 and 3, DAC 7, summing amplifier 8 with a resistor in the negative feedback circuit, controlled current source 9 , the source 10 of the reference voltage, the keys 11-17 and the control unit 18. The introduction of new elements and the formation of new connections between the elements of the device eliminates the additive component of the error due to the drift of the equivalent bias voltage of the comparison circuit and digital-analogue converters. 1 il. i (L ts9 N9 d ts9

Description

The invention relates to temperature measurements m5, namely, devices for measuring temperature using resistance thermal converters.

The purpose of the invention is to improve the measurement accuracy by eliminating the additive component of the error due to the drift of the equivalent shift bias of the comparison circuit and digital-to-analog converters.

The drawing shows a diagram of the device for measuring temperature

The device contains a resistance thermocouple, the first 2 and the second 3 model resistors, circuit 4 compare 1, the first digital-to-analog converter (DAC) 5 ,, the second ZAN 6, the third CDL 7, the summing amplifier 8 with the resistor in the negative feedback circuit , controlled current source 9, voltage source I), voltage switches 11 G /, control unit 18. As a control unit, a pulse generator with a counter and pulse shapers that generate control pulses of a certain duration can be used. The controlled current source 9 9 is a circuit 4 of comparison, 11АП 5-7, keys 11-17 can be performed on standard microcircuits according to the usual schemes.

The device works as follows

The entire measurement cycle takes four strokes.

In the first cycle, signals from the outputs 19–22 of the control unit 18 arriving at the installation inputs, PAP 5 and DAC 7 are set to the initial zero state and the keys 13 and 16 are closed. Then, the QC control input of the DAC 7 from the output 23 of the control unit 18 receives the signal of alternate rotation of the bits SH

At the moment of equality of the voltages at the inputs of the comparison, at its output ||, the signal arriving at the output 24 of the control unit, on which the control stops: the operation of SHSh 7, is normalized.

In this case, the 1-neck signal in the measurement circuit is balanced at the input-1: comparison circuits using the third LAP 7

, u, no.: f (o

242727

Where

five

YU

.

 15 20. 25

35

and,

9Ро

and

CHAl

Gr is the resistance of the potential circuit of the reference resistor 2 connected to the common bus of the device; signal interference, drift About the measuring circuit; equilibration voltage at the output of the DAC 7. The constructive arrangement of the model resistor 3 inside the device ensures the equality TQ t), then equality (l) transforms into equality (2)

Ugpo itch G 2)

The voltage thus obtained at the output of the 1 CRT 7 is saved for the time of the second cycle, in which the key 16 is open, and the key 7 is closed by a signal from the lock 25 of the control unit 18.

In the second cycle, the initial value is canceled. For this, the signal from the output 26 of the control unit, the key 12 is closed, the signal from the output 27 to the remote control input i. PAP 5, includes all of its bits, and control and feedback signals are sent to the control inputs of the DPL 6 from the outputs 28 and 29 of the control unit. In this case, an equilibrium is performed for the comparison circuit 4 with the help of LIAII b, which regulates the current in the oC5-phase resistor 3 to the equality of

ROC

-MdV + 1Kts

  ME-Che 4 + Ur

Ro)

(3)

,

de U (j3o - signal interference;

the voltage at the output of the GEL 5 for all included bits and.

i 4 / ilt SMOKC.

.- | f;

N ,, E,

R

Iuo

oc

i

the maximum code number for all the included bits of the first DAC, corresponding to the maximum measurement scale; resistance of the resistor matrix P-2P of the first DAC; sensor supply current; reference source voltage;

feedback impedance to the Amplifier;

resistance of the first reference resistor;

 - resistance change

thermal converter in the measurement range;

RU - initial resistance

P

thermal converter in diaz measuring range.

The magnitude of the resistance of the reference resistor 3 from the condition of obtaining the equality Hc .. (4)

o-t, °

Under this condition, and also taking into account the expression (2), the expression (3) takes the form:

R

the dependence of the measured temperature t on the code value of the DAC 5 in the form

,,

where k l4 Ro .U, (5)

- potential resistance

In the third cycle, the keys are open, and the keys 11 and the signals from the outputs 30 and 31 of the control unit 18. The inputs of the D / A converter 7 receive control and feedback signals 20 from the outputs 20 and 23 of the control unit, and the input to the D / A converter 5 is reset to the output of the output 19. The signal present in the thermal converter circuit is balanced at the input of comparison circuit 4 25 using the third DAC 7 until equality

1, „+ U, where

  sensor circuit connected to the common bus of the device.

The voltage thus obtained at the output of the D / A converter 7 is maintained for the time of the fourth cycle when the resistance thermocouple is energized. In this cycle, the key 11 is open, the keys 12 and 15 are closed by control signals from the outputs 26 and 32 of the control unit, and the control inputs of the DAC 5 receive control and feedback signals from the outputs 19 and 27.

The balancing of the comparison circuit in this case is carried out with the aid of a DAC 5 until equality

I + Uqpo + TuRx-t-RH U ftt, +

H

.

where dN is the measured value;

K, is the code of the measured value. The first and third terms of the left and right sides of the equation according to (4) and (6) are mutually exclusive, and equation (7) is converted into equation

i-ix-uofr- (8) which, when compared with equation (5), determines proportional

coefficient of proportionality.

The code of the digital register of the DAC 5 is proportional to the value of Ti. and respectively measured temperature.

Claims (1)

Invention Formula A temperature measuring device containing a thermocouple and a resistor 17, the first digital signal 14 is a closed converter, the first control input of which is connected to the first output of the control unit, a controlled current source, the control input of which is connected to the output of the second digital-analog converter, the first the output is connected to the common bus of the device connected to the comparison circuit, and the second output through (the first key, the control input of which is connected to the second output of the control unit, is connected to To the dead current output of a thermal converter of resistance, characterized in that, in order to improve the measurement accuracy, a reference voltage source, a key of keys, two exemplary resistors, a third digital-to-analog converter and a summing amplifier, the non-inlet input of which is connected to a common bus, are entered into it. device, the input input is connected to the outputs of the first and second digital-to-analog converters, and through the second switch and the first exemplary resistor is connected to the output of the reference voltage source, Nome with the reference inputs of digital-analog converters, and the output of the summing amplifier is connected to a first input of a comparison circuit whose output is connected The input of the control unit, and the second input 50, respectively, through the third and fourth switches are connected to the first potential terminals of the thermal converter and the second model resistor, the second 55 potential terminals of which are connected to the total device thickness, and the current terminals respectively that and the seventh keys are connected to bt35 40 45 (T) 12427274 the dependence of the measured temperature t on the code value of the DAC 5 in the form ,, where k 35 40 45 5i; i 727 s p (.My to the output of the controlled source of a toprepig), a quad, pt, and K.-1,) | here are additional options: one of the sixth keys and the remote control are connected to the corresponding digital-analogue transducer and to the control inputs of the second,. teli.