SU1464050A1 - Digital thermometer - Google Patents

Abstract

The invention relates to the field of temperature measurements and can be used in automated measurement and control systems. The aim of the invention is to improve the measurement accuracy by reducing the measurement error due to the instability of the parameters of the elements of the device. The imbalance voltage of the bridge circuit 1 is amplified by the actor 2 unbalance of the bridge circuit, made in the form of a differential pulse divider, and is fed to the first input of the amplitude phase detector 3, the second input of which receives the pulse voltage from the output of the control pulse generator 11. The amplitude of the pulse voltage at the output of the amplitude phase detector 3 is stored in an analog storage device 4 and then fed to the first input of the controlled frequency generator 5. The pulse voltage from the output of the controlled frequency generator 5 through the frequency divider 7, the shaper 8 bipolar pulses and the attenuator 9 of the pulse signal is fed to the diagonal of the power supply of the bridge circuit 1 and balances the bridge circuit by heating the thermistor 14 to a certain temperature. 2 Il. with S (L

Description

Amplitude Phase Detector 3, Analogue Phase Detector; to the log storage device 4, fig.2g - voltage U 5, dfd to the output-generator 5 controlled frequency, generator 6 of the reference frequency, frequency divider 7, driver. 8 bipol pulses, a pulsed signal attenuator 9, a power source 10, a driver of 11 control pulses, a subtractor of 12 pulses of the pulse phase detector at R-P-7 R o (solid line) and the voltage of the analogue output signal. 25 of the storage device at RT 7 R (dashed line), in FIG. 2 d the voltage and JHX dfvna on the output of the amplitude phase detector (continuous line) and the voltage U on vkh i- during the analog memory device

Conventions and meter 13 frequency.

A thermistor (thermistor) 14 with resistance R is connected to one of the arms of bridge circuit 1, and resistors 15–17 with resistance RP equal to resistance R in the other point are connected at the working point.

The temperature meter works as follows.

U unbalance voltage

Circuit 1 at RT-T RO is amplified by amplifier 2, made in the form of a differential pulse amplifier, and is fed to the first input of the amplitude phase detector, 3, the second input of which receives the pulse voltage from the output of the control driver 11 (Fig. 2) . The amplitude phase detector 3 generates at the output a unipolar pulse signal with an amplitude equal to the amplitude of the unbalance signal pulses and polarity determined by the phase shift between the pulses of the unbalance signal of the bridge circuit 1 and the pulses at the output of the control pulse shaper 11. The amplitude of the pulse voltage at the output of the amplitude phase detector 3 is stored in an analog memory.

a difficult phase detector; on fig.2g - the voltage U 5, at dfd at the output

de amgshield phase detector with R-P-7 R o (solid line) and voltage and cx AHF analog output. memory device at RT 7 R (dashed line), fig.2d shows the voltage and JHX dfvnna output of the amplitude phase detector (continuous line) and voltage U vkkh i- during analogue storage device (dotted line) at R. R,

 t Oh

Pulse frequency

f p at the exit

five

0

five

0

five

the controlled frequency generator depends on the difference of the voltages U b, x l e from the output of the analog storage device 4 and the initial bias voltage.

Impulse voltage from the output of the generator 5 controlled frequency through the divider 7 frequency shaper

8 Bipolar impulses and attenuator

A 9-pulse signal is fed to the diagonal of the power supply of the bridge circuit 1.

When the supply voltage of the bridge circuit 1 is turned on, the initial resistance of thermistor 14 is much greater than Ro and the bridge circuit is highly unbalanced, the frequency of the pulses generated by generator 4 at the initial moment of time is determined by the generator parameters, voltage Uj ,, and the value of the initial bias voltage Uj-i. Pulse voltage amplified by amplifier 2 unbalance of the bridge circuit and converted by a series-connected amplitude phase detector 3 and an analog storage device

, vom to voltage and, dz dc, changes the frequency of the pulses fj at the output of the generator 5 of the controlled frequency. In case of any imbalance in the balancing of the MOST090Y circuit, a pulsed voltage of one or another polarity will appear at its output relative to the impulses of the imaging unit 8 bipolar pulses depending on the direction of unbalance of the bridge circuit. The amplitude phase detector 3 and the analog memory 4 provide for extracting the imbalance of the bridge circuit of pulses of the desired polarity from the signal at the output of amplifier 2 and converting it into a proportional control voltage of the generator 5. The variable voltage npk changes the frequency fp and consequently, the heating power of the thermistor with a pulse signal before the initial balancing of the bridge circuit.

In this case, the heating power of the thermistor with a bipolar pulse signal (the feedback power of the self-balancing bridge circuit) is determined by the ratio

  -C-f p ROS r-r-n

where R t is the resistance of the thermistor at the operating point defined by the resistors 15-17 of the bridge circuit;

and - the amplitude of the bipolar pulsed signal applied to the thermistor; f P - the frequency of the pulses at the output of the generator 5 controlled frequency;

C - the duration of the pulses fed to the thermistor; n is the division factor of the frequency divider 7.

From this output, it is possible to determine the sensitivity S p of the self-balancing bridge circuit by the heating power

S - - R. s

2-and.-C

To avoid shunting the bridge circuit by output impedance

When exposed to the thermistor from the power supply source 10, and the investigator’s control of the environmental temperature, equivalent to the additional power of its heating, the RL,

but, to avoid reducing the amplitude of the pulsed signal, it should be performed as a current source.

Initially a breakdown of the bridge circuit occurs. However, the resulting imbalance signal then leads to a change in the frequency of the oscillator 5 of the controlled frequency, and consequently, its heating power by 4P, due to which the bridge returns to a balanced state. In this case, the frequency change at the output of the generator 5 is determined by the ratio

jf p 8r-yr

So-H-de H-4e

n rj

g

one

0

0

five

0

five

where h 5

0

constant dissipation of thermistor

0 - change in ambient temperature, p.

From this expression it can be seen that when compared with the prototype, when the same value Lb is applied to the thermistor, the change in the frequency Л is on, the output of the generator 5 is n times larger, which leads to an increase in the accuracy of

Reni,,,

one

The use of frequency divider 6 also makes it possible to almost completely eliminate errors due to the distortion of the rectangular shape of the pulsed signal and the instability of its multiplicity caused by fronts

IG PULSE.

The frequency divider 7 makes it possible to obtain the frequency of the pulse signal supplied to the thermistor, which is rather small, at which the duration S of the supply pulses is much longer than the duration of their fronts and the influence of the latter on the stability of the pulse area and their shape is practically absent. The driver 11 of the control pulses generates unipolar pulses of duration less than C located on the time axis within the first half of the bipolar p pulse (figure 2), thereby excluding the influence of the fronts of bipolar pulses on the operation of the amplitude phase detector 3.

To avoid shunting the bridge circuit by output impedance

but, to avoid reducing the amplitude of the pulsed signal, it should be performed as a current source.

o r mula

5,146,450

Invention

you and t

 A digital temperature meter containing a bridge circuit with a thermistor in one of the arms, connected by a measuring diagonal to the input of the imbalance amplifier of the bridge circuit, a power source connected to the power circuit of the bridge circuit, a controlled frequency generator, the output of which is connected to the first input of the subtractor of pulse sequences, the second input of which is connected to the output of the reference frequency generator, and the output is connected to the input of a frequency meter, a driver of bipolar pulses, the output of which is through an attenuator mpulsnogo signal coupled to the bridge circuit supply diagonal ,, wherein

by that

that, in order to increase the measurement accuracy, an amplitude detector1 phase detector, an analog storage device, a control pulse former and a frequency divider, the input of which is connected to the output of the controlled frequency generator, and the output connected to the input .

Q bipolar pulse generator, with the input of the amplitude phase detector connected to the output of the unbalance amplifier of the bridge circuit, which controls the input of the amplitude phase

The detector 5 is connected via a control pulse shaper to the output of a bipolar pulse shaper, and the output is connected to the input of an analog storage device, the output of which is connected to a controlled frequency generator.

and u ,,,) Q36H

S

iuprAfi d

%// one

g

eight

Claims (1)

Formula of the invention i Digital temperature meter containing a bridge circuit with a thermistor in one of the arms, connected by a measuring diagonal to the input of the unbalance amplifier of the bridge circuit, a power source connected to the diagonal of the bridge circuit power supply, a controlled frequency generator, the output of which is connected to the first input of the pulse subtractor sequences, the second input of which is connected to the output of the reference frequency generator 15, and the output to the input of the frequency meter, a bipolar pulse shaper, the output of which through the attenuator of the pulse signal is connected to the diagonal of the power supply of the bridge circuit, characterized in that, in order to increase the exact-> type of measurement, an amplitude phase detector, an analog storage device, a driver of control pulses and a frequency divider are introduced into it, the input of which is connected to the output of the generator controlled frequency, and the output is connected to the input of the bipolar pulse shaper, and the input of the amplitude phase detector is connected to the output of the unbalance amplifier of the bridge circuit, the amplitude control input one phase detector is connected through a shaper of control pulses to the output of the shaper of bipolar pulses, and the output is connected to the input of an analog storage device, the output of which is connected to a controlled frequency generator.