SU1339413A1 - Temperature measuring device - Google Patents

Abstract

The invention relates to instrumentation. The purpose of the invention is to improve the accuracy of temperature measurement. The device performs a push-pull measurement algorithm, it contains a thermocouple 1, a stabilized voltage source 2, amplifiers 3 and 11, a bridge 4, consisting of a resistance thermometer 5, a reference resistor 6, exemplary resistors 7 and 8 , capacitors 9 and 10, keys 12-19, resistors 20 and 21, 37 and 38, null organ 22, control unit 23, AND-HE elements 28, 29, And 30-33 elements, inverter 34, RS flip-flop 35 , the recorder 36 and keys 39 and 40. To eliminate the multiplicative component of the error introduced by the measurement HAND measuring path gain, the device is calibrated in four cycles by commands from the control unit 23. 1 il. С /) J ... 00; about 4 00 SchT

Description

The invention relates to instrumentation and can be used in temperature measurement systems using thermoelectric converters (thermocouples).

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

The drawing shows a functional diagram of the proposed device.

The device for temperature measurement contains a thermocouple 1, a stabilized voltage source 2, an amplifier 3, a thermocouple free end temperature compensator - bridge 4., consisting of a resistance thermometer 5, a reference resistor 6 and two exemplary resistors 7 and 8, two capacitors 9 and 10, the second amplifier 11, eight switches 12-19, two resistors 20 and 21 in the negative feedback divider, the first amplifier 3, the zero-organ 22, the control unit 23 with outputs 24-27, two IS-NOT elements 28 and 29 , four elements And 30-33, an inverter 33, RS-trigger 35 and the recorder 3 with Source inputs, in which any recording device (for example, magnetic or photo-optical) with an analog input voltage, resistors 37 and 38, two keys 39 and 40 can be used. Control unit 23 includes a clock generator, a pulse counter and a decoder ( not shown).

The device performs a push-pull measurement algorithm and operates as follows.

By the signal 24c of the control unit 23, the keys 12-16, 18, 19 and 40 are turned on in the first measurement cycle of the conversion, as a result, the capacitor 9 is connected to the thermocouple 1 via the compensation bridge 4 and charged to the voltage

Ue, and, EMF + and, ",,, (1) where and is the voltage across the capacitor 9,

EMF - thermocouple signal; voltage at the output of the compensation bridge. The capacitor 10 is connected to the non-inverted input of the second amplifier 1 1 and is connected via a switch 9 to the output of the second amplifier 11 an inverted input of which is connected to the output of amplifiers 3 and 11, the non-inverted inputs of amplifiers 3

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and 1 are connected via keys 18 and 40 respectively to a common point. As a result, capacitor 10 is charged until the voltage

five

0

 C2

 jpi:

five

0

where and. - the voltage on the capacitor 10;

U- is the drift voltage O of the first amplifier;

Unpj is the drift voltage O of the second amplifier.

In the second measurement cycle, the keys 17 and 39 are turned on by the signal 25 from the control unit 23, and the others are disconnected. As a result, the capacitor 9 is connected via the switch 17 to the non-inverted input of the amplifier 3, and the capacitor 10 through the switch 39 to the non-inverted input of the amplifier 11, inverted the input of which is connected to the output of the amplifier 3, at. this at the output of the amplifier 11 is formed voltage

K, - K, + IR, +

 (3)

respectively, the transmission coefficients of amplifiers 3 and 11, which are determined by the formulas

11 T1.

 OUT C1

+ and

where k

fpi and K

- and

0

TO,

/ Rii

 R

20

R.

TO,

 5j &

TO

(four)

37

where, k, and k,, -b are the resistances in the negative feedback circuit of amplifiers 3 and 11, respectively.

RM, K, V.

Substituting the values of U from formulas (1) (2) and (4) into formula (3), we obtain the relation

; (EMF + u. ,, J (i + n-S

and

out

 R

go

R

(five)

7

In which there is no additive component of measurement error introduced by the drift of amplifiers 3 and 11. The result of the recording on the recorder is determined by the ratio

0

N. K.

and.

  TO

X OB,

and.

(6)

0 & UI,:: general, where N is the reading on the recorder;

and. - EMF + and ,,, „;

K, is the total transmission coefficient of GEN

measuring path.

In order to eliminate the multiplicative component of the error introduced by g by changing the transmission coefficient of the measuring path, the device is calibrated in four cycles by commands 26 and 27 taken from control unit 23. In this case, in the first measure

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The keys 12, 14-16, 18, 19, and 40 are turned on the gauge, and the key 13 is turned off by the signal 26 through the element 31 and as a result, the capacitor 9 is charged before the voltage

and ,,,, EMF - and ", (7) where and is the voltage across the capacitor 9 in the first calibration cycle;

EMF - thermocouple signal; and - the voltage across the compensation resistor

the bridge

and the capacitor 10 is charged before the voltage determined by the formula (2). In the second calibration cycle, the keys 17 and 39 are turned on, and all the others are turned off, and the output voltage of the amplifier I1, determined by the formula (3), has the meaning

i.h, x (emf-i,) (| -. I). (eight}

At the same time, at the output of the null organ 22, the sign of the output voltage is determined, if a logical 1 signal appears at its output, which corresponds to the + sign, then the element AND 33 and the trigger 35 are opened, the signal from which in the third calibration cycle through the elements 28 and 30, the key 12 is turned off, while the keys 13-16, 18, 19, and 40 are turned on, as a result, the capacitor 9 is charged before the voltage

,., EMF, (9) where and., j is the voltage across the capacitor 9 in the third calibration cycle, and the capacitor 10 is charged to a voltage determined by the formula (2). In the fourth calibration cycle, the keys are in the same state as in the second cycle, i.e. Keys 17 and 39 are enabled, and all others are disabled. Then the voltage at the output of the amplifier 11 in the fourth calibration cycle, taking into account the formula Sz), has the value

and

 R

R8YH

 EMF. (| + 1) .5-. (ten)

R

R,

20 3

The difference between the output voltages obtained in the second and fourth calibration cycles and calculated by formulas (8) and (10) is the value determined by the formula

and u. (- 1). | - S, (11)

° "go Kji

where and is the voltage across the reference resistor Rg, determined by the formula

3

.1 Е R.

R ,,. + R.

(12)

 Arr about

where E is the voltage of the stabilized source included in the diagonal of the bridge; R - Resistance exemplary reQop

a resistor connected to the other shoulder of the bridge, adjacent to the reference resistor,

and the result of recording on the recorder is determined by the ratio

N,

 TO.

Wow.

(13)

NO

 -, stand OBY, about

where is the definition of K

we put it in formula (6) and get the value of the measured value

(14)

and. about

If a logical O appears at the output of the null organ 22, then the AND element 33 does not open and the trigger 35 remains in the closed state, and the signal from its inverse output in the third cycle through the elements 29 and 32 disconnects the I 4 key, I, 2, 13, 15, 16, 18, 19, and 40 switches are turned on, as a result, the capacitor 9 is charged before the voltage

and

With KJ

 EMF - and, „„ „+ and,, (15)

where and, |., is the voltage across the capacitor 9 in the third calibration cycle;

UI Q is the voltage at the output of the compensation bridge; Ug is the voltage across the second resistor.

The voltage on the second capacitor 10 is determined by the formula (2). In the fourth calibration cycle, the keys I7 and 39 are turned on, all others are turned off and the voltage at the output of the amplifier II in accordance with the force (3) has the value

and „(EMF + and,„ „„ - ь Uj. (+1

 "about

X 5l

R

(sixteen)

37

The difference between the output voltages obtained by formulas (16) and (5) is the value determined by formula (11), i.e. regardless of the sign of the calibration voltage obtained in the second cycle, the calibration voltage drop remains constant in either case, determined by the voltage according to the formula. (l2), and the measurement result is determined

mc according to formula (14) and does not depend on the transmission coefficient of the measuring path, and, therefore, does not have a multiplicative error component. The measurement accuracy according to formula (14) is determined by the stability of the reference voltage Ug, and since this value according to formula 12) is a model measure, the measurement result has a correspondingly high measurement accuracy.

Claims (1)

Invention Formula A temperature measuring device containing a thermoelectric converter, a measuring amplifier, a temperature compensator for the free ends of a thermoelectric converter, was made in the form of a four-arm resistive bridge with a resistance thermometer in one of its arms connected in series with its measuring diagonal with a thermoelectric converter, a stabilized voltage source connected to the supply diagonal of the resistive bridge, and a recorder, characterized in that, in order to To increase the measurement accuracy, two capacitors, a second measuring amplifier, ten controllable electronic switches, a null organ, two NAND logic gates, four AND gates, an inverter, an RS flip-flop and a control unit, the first electronic the key is connected to the bridge diagonal in series with a source of stabilized voltage, the second and third electronic keys are connected one by one with the bridge resistors to its symmetrical arms with respect to the supply diagonal, one of the capacitors is connected through the fourth and fifth electronic switches in parallel to the circuit of a series-connected thermoelectric converter and compensator for the temperature of its free ends and through a switch the electronic switch is connected to the non-inverting input of the first measuring amplifier, the inverting input of which is connected to its output through a resistive voltage divider and its non-inverting the input is connected via the seventh electronic 136 the key with the common bus of the device, the second measuring amplifier is made in a differential circuit and connected with its inverting input through the resistor of its negative feedback circuit to the output of the first measuring amplifier, the second capacitor is connected via the eighth electronic switch to the output of the second measuring amplifier and via the ninth electronic switch - to its non-inverting input, which through the tenth electronic key is connected to the common bus of the device, the null-organ is turned on by its input at the output of the second meter Amplifier, one inputs of the first, second and third logic elements And are connected to the first output of the control unit connected to the control inputs of the fourth, fifth, seventh, eighth and tenth electronic keys, the second output of the control unit is connected to the control inputs of the sixth and the ninth electronic keys and the first input of the fourth logic element I, the outputs of the first, second and third logic elements I are connected respectively to the control inputs of the first, second and third electronic keys o, the second input of the first logical element AND is connected to the output of the first logical element NAND, the first input of which is connected to the output of the RS flip-flop, the second input of the second logical element AND is connected to the third output of the control unit, the second input of the third logical element AND is connected to the output the second logical element AND-NOT, the first input of which is connected to the inverse output of the RS flip-flop, the second inputs of the logical elements AND-NOT connected to the fourth output of the control unit, the second input of the fourth logical element It is connected to the output of the zero-organ, and its output is connected to the S-input of the RS-flip-flop, whose R-input through the inverter is connected to the third output of the control unit, the first input of the recorder is connected to the output of the second measuring amplifier, the second input to the second output of the control unit , and the third and fourth inputs of the recorder are connected to the outputs of the first and second NAND logic elements, respectively.