SU1303849A1 - Digital temperature meter - Google Patents

Abstract

This invention relates to thermometry. The purpose of the invention is to increase the accuracy of measurement by reducing the measurement error caused by the instability of the elements of the meter. The device contains a voltage source 1, a switch 2, operational amplifiers 3 and 10, an exemplary resistor 4, connecting wires 5,6,7 and 8, a thermistor transducer 9, switches 11 and 12, an amplifier-accumulator 13, a bias voltage source 14 , switch 15, integrator 16, null organ 17, control block 18, counting pulse generator 19, polarity determining block 20, selectors 21 and 22, functional converter 23, readout device 24 and reversible counter 25. Introducing new elements and forming new connections between The elements of the device allow the measured temperature value to be determined by finding the difference between the results of two push-pull integrating transformations of the output voltage of the amplifier-adder 13 to the pulse code, obtained when the reference voltage is connected to the source 1 and the subsequent functional transformation of this difference. 1 ap f-ly, 5 ill. , SS SL CA: o DO eo 4 x Fiá.1

Description

The invention relates to thermometry, namely to secondary devices for temperature measurement by contact method using thermal resistance transducers. The advantages of the proposed device are manifested when used in digital panel meters for temperature measurement with thermo-resistive transducers connected to the device using a three- or four-wire connecting line. It can be used in measuring the deviation of resistance from some given value.

The aim of the invention is to improve the measurement accuracy by meHtje by reducing the measurement error caused by the instability of the elements of the meter.

Figure 1 shows a structural electrical circuit of the device .; figure 2 - diagram of the amplifier-adder; on fig.Z - diagram of the coding part of the device; figure 4 - timing charts of his work; FIG. 3 is a diagram of a functional converter.

The device contains a source of reference voltage 1, an electronic switch 2, the first operational amplifier 3, an exemplary resistor 4, the first current 5, the first potential 6, the second potential 7, the second current 8 connecting wires, a thermistor resistor 9, the second operational amplifier 10, the first 11 and second 12 mechanically coupled switches, amplifier-adder 13, bias voltage source 14, switch 15, integrator 16, null organ 17, control unit 18, counting pulse generator 19, polarity determining unit 20, first 21 and second 22 selectors, functional converter 23, digital reading device 24, reversible counter 25. Amplifier-adder 13 contains the first 26 and second 27 operational amplifiers, the alternating resistor 28, the first 29, the second 30, the third 31 are permanent resistors. The control unit 18 contains a frequency divider 32, a ring counter 33, the first 34, the second 35, the third 36, the fourth 37, the fifth 38 and the sixth 39 RS triggers, the D-trigger 40, the first 41, the second 42, the third 43 and the fourth 44 elements OR, first 45, second 46, third 47 and fourth 48 pulse transformers, first 49, second

five

0

five

0

five

0

five

0

five

50, third 51 and fourth 52 elements And, a modulo two adder 53. The second selector 22 contains the first 54 and second 55 elements I. The source 1 of the reference voltage is connected in parallel to the fixed contacts of the electronic switch, one of its terminals is connected to a common pgana, and the second with the input of switch 13. The first operational amplifier 3 has a separate power supply. The inverting input of this operational amplifier is connected to the moving contact of the electronic switch 2, and the non-inverting input is connected to the midpoint of its power source and is connected to the common bus of the device through the reference resistor 4. The output of the first operational amplifier 3 is connected to the first fixed contact of the first switch 1 1 and through the first current connecting wire 5 to the first output of the thermosetting converter 9, which through the first potential connecting wire 6 is connected to the second fixed contact of the first switch 11. The second output of the thermoresistive converter 9 through the second potential connecting wire 7 is connected to the inverting input of the second operational amplifier 10, and through the second current will connect flax wire 8 - with the output of the second operational amplifier 10 and a first fixed contact of the second switch .12. The non-inverting input of the second operational amplifier 12 is connected to the common bus of the device. The first input of the amplifier-summer 13 is connected to the sub-terminal of the first switch 11, the second input to the moving contact of the second switch 12, the third input to the non-inverting input of the first operational amplifier 3, The outputs of the amplifier-13 and bias voltage source are connected to the input of the switch 15 , the output of which through the integrator 16 and the zero-body 17 is connected to the control unit 18. The output of the counting pulse generator 19 is connected to the control unit 1B, the first selector 21 and the digital function converter 23 are connected to a digital reading device 24, and through the second selector 22 to the summing and subtracting input of the reversible counter 25, the output of which is connected to block 18. Control The control unit outputs are connected to an electronic switch 2, a switch 15, a polarity detection unit 20, a digital function converter 23, and a digital counter 24. The amplifier-adder 13 has three inputs. The non-inverting input of the first operational amplifier 26 serves as its first input. The second and third inputs of the amplifier -cumulator 13 through respectively the variable 28 and the first constant 29 resistors are connected to the inverting input of its second operational amplifier 27, the third constant resistor 31 is included in the negative feedback circuit. The first operational amplifier 26 Amplifier - summer 13 is included as a voltage follower, the output of which is connected via a second precision resistor with the inverting input of the second operational amplifier. The output of the first operational amplifier 26 is connected to the common bus of the device, and the output serves as the output of the amplifier - accumulator 13.

The value of the measured temperature is determined by finding the difference between the results of two push-pull integrating conversions of the output voltage of the amplifier-adder into the number of pulse code obtained when connected to the source of the reference voltage, or to the common bus of the inverting input device of the first operational amplifier 3 and the subsequent functional transform that difference. When the device operates with a thermo resistive converter 9, connected using a four-wire connecting line, switches 11 and 12 are in the lower position in FIG. 1, and when working with a thermal resistance converter 9, they are connected using a three-wire connecting line, the first potential wire 6 is absent, and switches 11 and 12 are located in the upper position in FIG.

The device works as follows.

In the initial state, the inverting input of the first operational amplifier 3 is through an electronic switch 5

5 o 5 0

five

Tel 2 is connected to the device common bus, reversible counter 25, digital function converter

23 and digital reading device

24 revoked In the first cycle of operation of the device, the sum of the output voltage of the amplifier-adder and the bias voltage source is converted into a number-impulse code by a push-pull integration, which through the second selector 22 is fed to the summing input of the reversible counter 25. Thus, at the end of the first conversion cycle in the reversible the counter will be recorded number

N ow gr (1)

Uq

where, the output voltage of the amplifier is a summator 13;

P (, is the bias voltage; U is the drift of the equivalent bias voltage of the integrator 15 and the null organ-18;

UQ is the voltage of the source 7 of the reference voltage;

T is the voltage integration time.

At the end of the first conversion cycle, the inverting input of the first operational amplifier 3 is connected via switch 2 to the source 1 of the reference voltage. In the second cycle, the sum of the output voltage of the amplifier-adder 13 and the source 14 of the bias voltage is converted into a number - a pulse code. In both cycles of conversion, the number - pulse code is formed by applying the pulses of the frequency f of the generator 19 to the counting pulses, the time interval formed between the beginning of the discharge of the voltage integrator 16. Uj5 and the processing time of the null organ 17. In the second cycle, with the start of the integrator 15 discharge, the control unit 18 permits the passage of pulses to the subtracting input of the reversible counter 25 until it is zeroed. The signals passing to the control unit 18 from the null organ 17 and the reversible counter 25, signaling the response of the null organ and zero crossing of the reversible counter, serve to form a time interval over which the pulses from the generator 19 are counting them to 51,338,496

pulses through the first selector 21 will be able to record the output voltage will be sent to the functional preamplifier amplifier with three: wired to (and

and the three-wire connection of the thermistor resistor 24. Thus, the number of pulses will pass to the functional converter

I

N N, -N, fcU

-Tf.

(2)

m - Tf. 2O

UO b Mj, n

(3)

The output voltage of the amplifier is the sum of & a 13 can be defined as

-.

(four)

the voltage at the respective inputs of the amplifier-summer, the equivalent drift of the amplitude, and the summer; equivalent bias voltage from thermoelectric power, -shopper-. connecting lines.

with a three-wire resistive transducer

U, I (R, -b ,,) - & y. ,,

. + Lou ,,

U ,,,

where V is the resistance of the first current wire 5;

(S1

y is the resistance of the second current wire to the receiving UIJ2. - equivalent drift of the second .- 0 - th operational amplifier lOi

g is the voltage at the inverting input of the first operational amplifier 3,

45

N

(41

η is the equivalent drift of the first operational amplifier with four-wire connection.

(8) (9) (10)

(,) / (R «// R,), (11) 55

where R .., R, - resistance resistors, respectively, 4 and 29.

It is possible to record the output voltage of the amplifier of the adder with three: wired to (and

and

(four)

s

and the three-wire connection of the thermal resistance "

GO converter as

Ugn /,

(R // R / R

fO

4. UA1 + -1 1 -Ayi- + -) R +

R RH + R, R Rt,

OS

L

one

(12)

Workshop (RT / RTT

- R

R - o

(13)

where R. is the resistance of the resistor 31.

Taking into account that Ug in the first cycle takes the value O, and in the second UQ and substituting in the expression (2), W

, H1

reading and ;; and at these values

Uj, we get

 y.tsp

where R is the resistance of the resistor 30. Taking into account that (l + ott + / t ° + + ....) and providing

are learning

D -R.Jjl- RR

 Mind rh + r

R.

(S1

we get 0

02,

Ro (ott% | ir + ...) R

OS

1 +

five

N

(41

un Uo

. about . „.Х2

Tf. , (sixteen)

 Ro (oi- 1: + Pt + ...) Rot t.: / .,4

t (7

1 J. IDIP

where Rn is the resistance of the resistor 28. Functional converter 23 models the 0 F dependence (Rg-Rp). Thus, having passed through a functional pulse converter, it is converted into N pulses,

(18)

N b.

For normal operation of the device, the source 1 of the reference voltage and the source 14 of the bias voltage must be of opposite polarity. The value of U. is determined by the ratio

neither

/and

out, mox

/,

(nineteen)

fO

f5

where Ujjj, j, | ddc (, is the output voltage of the amplifier-summator at

The control unit, apart from the initial installation of the control circuit of the switch 15 and switch 2, the generation of the time interval T by the generator 19, the zeroing of the response of the zero-body 17 and zero crossing of the reversible counter 25, the control of the selectors 21 and 22, determines the sign of the measured temperature. The sign of the measured temperature is determined by the polarity of the voltage 20 If C or then Ugj ,, p, or N N, i.e. in the second cycle, the zero-body conversion 17 is triggered after zero crossing of the reversible counter 25, which will be fixed by the polarity determination unit 20 and will show the sign

and p l - lo.

25

yy oh

 -. C, Rg RO ,, i. the zero-body 17 will operate before the zero-crossing of the reversible counter 25, and the polarity determination unit will show +.

The control unit 18 operates as follows.

Frequency divider 32 at the frequency f of the generator of counting pulses generates pulses with a period of T. The ring counter 33 cyclically forms the pin of time-shifted pulses of duration T. On the leading edge of the first and fourth pulses, the beginning of the first integration pulse, the second and fifth pulse at the output of the third pulse transformer 47 - the start signal of the second integration cycle, the sixth pulse through the first pulse transformer 45 - signal al start of the first conversion cycle. These signals are captured by the first 34, second 35, and third 36 RS triggers. The fourth RS-flip-flop 37 captures the actuation of the zero-organ 17. The second 35, the third 36 and the fourth 37 RS-flip-flops are reset to zero by the installation signal to the unit of the flip-flop following it.

35

0

thirty

40

O

five

0

five

The first trigger 34 is reset to zero by a zero-body trigger signal. The output of the first RS flip-flop 34 controls the switch 2, the second 35, the third 36 and the fourth 37 RS-flip-flops - the operation of the switch 15. The switches of the switches 15 are produced by a single level at the output of the second 35, third 36 and fourth 37 RS-flip-flops. The second RS flip-flop 35 sets the integration time of the output voltage of amplifier-resistor 13 and bias voltage source 14, the third 36 connects voltage source 1 until the zero-body 17 triggers, quarter 37 triggers integrator 16 before the first conversion cycle begins. The zeroing of the integrator 16 is performed by connecting the output of the zero-body 17 to the input of the integrator 16 through the switch 15. The output signal of the fourth pulse transformer 48, indicating the operation of the zero-body, and the zero crossing signal of the reversing counter 25 are fixed by resetting to zero respectively 38 and the sixth 39 RS-flip-flops. The sequence of their operation is fixed by D-flip-flop 40 by writing to it the state of flip-flop 38 at the moment of passing the zero-crossing signal of the reversible counter 25. Thus,

5 at b 0 ° С at the output of the D-flip-flop a zero level will be set, and at C - a single level. The D-flip-flop output is used to determine the sign and control of the function transducer 23, the command for enabling the passage of pulses from the generator 19 to the summing input of the reversing counter according to the state of the fifth RS flip-flop 38 and the second output of the ring counter

 forms the third element And 51. The command for enabling the passage of pulses to the subtractive input of the reversible counter 25 until it is zeroed forms the element And 52. The adder over

0 module two 53 analyzes the state of the fifth 38 and sixth 39 RS-flip-flops. If their states do not match, the element 53 switches to the single state, which in the second cycle of the second conversion cycle serves as a signal for allowing the passage of pulses from the generator 19 to the functional converter 23 .

0

0

Functional Converter (AF) 23 can be performed according to the scheme shown in figure 5. It contains a binary frequency multiplier 56, a counter 57 of the length of the approximation section, a shaper 58 of pulses, a persistent storage device (ROM) 59 and a counter of the number of approximation sections 60. The functional converter 23 performs a piecewise linear approximation of the dependence F (RQ- RQ). - Approximation is performed according to the program recorded in the ROM. In the ROM, the conversion coefficient Np of each approximation area is recorded. The value N sets the conversion factor of the binary frequency multiplier 56, and Np sets the duration of the approximation section in counter 57. Pulse sequence corresponding to the result of the conversion (RQ-RQ) into a digital code

Nr

R

enters the multiplier 56, where it is divided by the coefficient K. The pulses from the output of the multiplier 5 are fed to the indication and the counter of the length of the plot of approximation. When counter 57 passes through its zero, an impulse is formed at its output, which leads to an increase in the content of counter 60 per unit, i.e. change the address fetch the contents of the ROM. At the outputs of the ROM, the following value is set, and,. On the falling edge of the pulse arriving at counter 57, pulse shaper 58 generates a pulse of preset counter 57. As a result, counter 57 records the code Ng; c.;,. Upon initial installation, the counter 60 drops to zero, and the counter 57 records the code N

Dt-n

Claims (2)

1. A digital temperature meter containing an exemplary resistor 0 five 0 five 0 -50 five thermistor converter, connected to the potential and current wires of the communication line, electronic switch, the first fixed contact of which is connected to the common bus meter, the switch, the first and second inputs of which are connected respectively to the outputs of the amplifier and the bias voltage source, and the output through the series the connected integrator and the zero-organ are connected to the first input of the control unit, the second input of which is connected to the output of the reversible counter, and the outputs are connected respectively A to the control inputs of the electronic switch, switch, first and second selectors, the polarity detection unit of the digital reading device and the functional converter, the output of which is connected to the input of the digital reading device, and the input connected to the output of the first selector, the input of which is connected to the generator output reference frequency connected to the third input of the control unit and the input of the second selector, the outputs of which are connected to the summing and subtracting inputs of the reversible counter, distinguishing In order to improve measurement accuracy by reducing the measurement error caused by instability of the meter elements, two operational amplifiers, a reference voltage source, and two mechanically connected switches, the first fixed contacts of which are connected to the outputs of the first and second operational amplifiers, are introduced into it , the second fixed contacts are connected respectively to the first potential wire and the common meter bus, and the movable contacts are connected respectively to the first and the second inputs of the amplifier-summer, the third input of which is connected to the non-inverting input of the first operational amplifier and the midpoint of its power source connected through an exemplary resistor to a common meter bus connected to the first output of the reference voltage whose second output is connected to the third input of the switch and to the second fixed contact of the electronic switch, the moving contact of which is connected to the inverting input of the first operational amplifier, the output of which is connected to the switch thermal current transducer, the second current wire of which is connected to the output of the second operational amplifier, the non-inverting input of which is connected to the common bus meter, and the inverting input is connected to the second potential wire of the thermal resistance transducer, while the fourth input of the switch is connected to. null organ output 2. A temperature meter according to claim 1, characterized in that the amplifier-adder contains two operational amplifiers, three permanent and one variable resistor, with the first input of the adder amplifier connected to the non-inverting input of the first operational amplifier, the inverting input of which is connected to its output and through the first constant resistor is connected to the inverting input of the second operational amplifier connected via alternating and second and third permanent resistors respectively with the second and third inputs of the amplifier - the adder and its output connected to the output of the second operational amplifier, non-inverting input of which is connected to the common bus meter. To mmmut 5 K switch. 2 7r 7r Eg ST ffr fr Zr 3t 4r fr ffr nl Mr uHfuftoifu / ff Editor E. Sligan puff.S Compiled by V.Kulikov Tehred L. Serdyukova Proofreader L. Patay Order 1296/40 Circulation 777 Subscription . VNIIGSh of the USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, 4/5 Raushsk nab. Production and printing company, Uzhgorod, Projecto st., 4