SU1751849A1 - Resistance-to-code converting device - Google Patents

Abstract

The invention relates to electrical measuring equipment and can be used to measure the ambient temperature. The aim of the invention is to improve the measurement accuracy. The device contains a transformer bridge with an inductive current comparator, an equilibrium pointer, a digital automaton, a balancing device, made on current generators with keys. New in the device is that the balancing of the bridge circuit is produced by a current proportional not only to the code, but proportional to the code and current through the measured resistance, which provides a linear conversion of the measured resistance to digital code 1 or

Description

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with

The invention relates to electrical measuring equipment and can, in particular, be used for highly accurate temperature measurement using resistance thermometers in oceanographic equipment.

The purpose of the invention is to improve accuracy.

The drawing shows the block diagram of the device.

A device for converting resistance into a code contains a source 1 of a pulsed voltage, a transformer 2 of a voltage with a primary 3 and a secondary 4 windings, an element 5 of the measured resistance connected in a three-terminal measuring circuit (6-8 - terminals for connecting the resistance) resistance inductive comparator 10

currents with two input 11 and 12 windings, compensation 13 and output 14 windings, pointer 15 equilibrium, control unit (digital automat) 16, balancing device 17

The power supply source 1 serves to generate voltage pulses in the primary winding 3 of the voltage transformer 2 and can be performed according to any known scheme. The voltage transformer 2, the element 5 of the measured resistance, the element 9, the inductive current comparator 10 form a bridge measuring circuit, built according to the type of a transformer bridge with an inductive current bridge Mostov, the measuring circuit is designed to generate an error signal when the value deviates

Vj

SL

00

Ј

Yu

measured resistance Rx from the initial value R0

The balancing device 17 can be performed according to any DAC scheme with a transfer function corresponding to the dependence of the output current flow from the supplied code (MTek) expressed by the formula

IBX K Mtek

tech

N

Max

where IBX is the input current of the balancing device;

K is the coefficient of proportionality between the input current and the low-order current;

Mmax is the maximum code value.

The balancing device 17 can be performed, for example, on an integrated circuit chip of the type DAC K594RP1, which is a series connection of an operational amplifier with a set of output current generators. Each output current generator is assembled according to the same type on a transistor with a resistor in the emitter circuit and a key in the collector circuit. Generators are designed to receive currents that are distributed according to binary law, i.e. the current of each subsequent more than 2 times the current of each previous. This distribution is obtained by connecting the resistors of the current generators in the form of an R-2R resistive matrix. The keys in the collector circuits are used to sum the currents from the generators in the compensation winding of the inductive current comparator depending on the control code from the digital machine 16 applied to the control inputs of the keys (digital inputs of the balancing device 17).

The digital automat 16 may be more complementary according to a bit-balancing register scheme with a control circuit and a clock generator, for example, on a typical K155IR17 chip.

The device works as follows.

With the initial value Rx of the element 5 of the measured resistance, the bridge consisting of the transformer 2, the element 5, the input resistance of the balancing device 17, the element 9, the inductive current comparator 10 is balanced by the current through the element 9 with the resistance Ho. In the current comparator 10, the magnetic flux F1 from the current in the winding 11 with the number of turns "and is compensated by the magnetic flux F2 from the current in the winding 12 with the number of turns hell. The balance equation of the bridge

F1 F1 O

(D

When the measured resistance changes, for example by the value of ARX, the current in the winding 11 changes, and the magnetic flux Φ | The compensation of the difference between the magnetic fluxes Ft and Fg will occur through the magnetic flux Fz from the output current of the balancing device 17 passing through the winding 13 with the number of turns (Oz. Compensating the difference of the magnetic fluxes will occur after the end of the balancing process.

The balancing takes place as follows: The digital automat 16 alternately, starting with the highest bit,

0 includes the current switches of the current generator of the balancing device 17. For each enabled discharge, the source of pulsed power 1 issues a voltage pulse Ui through the voltage transformer 2 in the circuit of the measured resistance and element 9. At the same time, the input current of the balancing operational amplifier is through measured resistance, and change in output current

0, the opamp will be proportional to the change in current through the measured resistance.

At the output of the current keys of the current generator will be the sum of the currents from the connected

5 current generators. In this case, since all current generators are controlled by the same operational amplifier standing at the input of the balancing device, at their outputs the current will be proportional to the input current IBX, and the ratio of the output currents from each current generator will be determined by the ratio resistors about their emitter circuits When bit-wise balanced by binary code

5 this ratio is distributed according to the binary law, i.e. the current of each subsequent generator is two times less than the current of the previous current generator. Therefore, the current value at the output of current switches is:

0

lex K NTBK / n

out

1tek

N

Max

where IBX, 1st Edema) are the currents at the input and output of the balancing device, respectively;

K - coefficient of proportionality between the input current balancing

the device 17 and the current low-end current generators.

A set of current at the output of the balancing device 17 will take place before obtaining the total magnetic flux from the fluxes F1, Fg, F} equal to zero.

To reveal the linear dependence of the code on the measured resistance, we solve the balance equation of the bridge transformer measuring circuit

F1-F2 + Fz 0.

Expressing the balance equation of the bridge through the currents in the windings and the number of turns, we get: 15

 - iwn + 0.

where And, la-currents through the first 11 and second 12 input windings of the comparator 10 currents;

h - the current through the winding 13 compensation (z tech) - the current at the output of the balancing device 17).

After balancing, the change in the magnetic flux from the current change through the measured resistance is equal to the compensation magnetic flux from the output current of the balancing device 17 induced in the compensation winding 13 of the inductive current comparator 10. The balance equation of the bridge will write:

  ,

where А И is the increment of the current in the circuit of the measured 35th resistance 5 when its value changes by the value of Д R0.

in us

AR

ho

RXQ RBX + A RXQ

where 1inst is the initial value of the current in the target of the measured resistance RXo before incrementing it by the value of A RXo, 45

RBX is the input impedance of the balancing device 17.

The input current of the operational amplifier of the balancing device 17 is equal to

k5 °

U1 (7)

Ibx

RXQ + RBX + A Rxo

Delivered (T) in (2). we have

U1 K Mtek

tech

(Rxo + RBX + A Rxo) Nwa.cc

Delivered (6) and (8) in (5), we get NMSKC

Ytek A RXO

shg to (RXO 4-RBX)

.(9)

Thus, by introducing a current through the measured resistor to the input of the balancing device 17, we reach the linear conversion resistance - code.

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Claims (1)

Apparatus of the Invention A device for converting a resistance into a code containing a source of pulse voltage, the outputs of which are connected to the terminals of the primary winding of a voltage transformer, the first terminal of the secondary winding of which is connected to the first terminal of the measured resistance element, the inductive current comparator with the first input, compensation and output windings, a balancing device, the control digital inputs of which are connected to the corresponding control outputs of the control unit whose input connected to the output of the equilibrium indicator, the inputs of which are connected to the output winding of the inductive current comparator, the first output of the compensation winding of which is connected to the output of the balancing device, and the second output of the compensation winding and the first output of the first input winding of the inductive current comparator are common bus element of exemplary resistance, characterized in that, in order to increase accuracy, a second input winding is introduced into the inductive current comparator, hooray-., the weighing device is made on the multiplying digital-to-analog converter, and the control unit is arranged on a sequential approximation register, with the second terminal of the measured resistance element connected to the non-inverting analog input of the multiplying digital-analog converter, the inverting input of which is connected to the common bus, the first output of the second input winding of the inductive current comparator through the sample resistance element connected to the third terminal of the element of measured resistance; the second terminals of the first and second input terminals approx comparator inductive currents are combined and connected to the second terminal of the secondary winding of the transformer voltage.