SU1645902A1 - Method of determining velocity of gas or liquid flow - Google Patents

Abstract

The invention relates to a measurement technique and can be used to measure the velocity characteristics of flows of liquids or gases. The aim of the invention is to reduce labor costs and improve measurement accuracy. First, the calibration of the hot-wire anemometer is carried out. Key 7 is set to position a. The voltage is chosen such that the current in the circuit, consisting of a resistor 3 and a thermistor 2, does not cause the latter to self-heat. The thermistor 2 is placed in the flow at the minimum speed and its temperature is determined. Then the switch 7 is set to the position b, the thermistor 2 is included in the negative feedback bridge circuit, and measured

Description

The invention relates to a measurement technique and can be used in the development of multi-channel thermo-anemometric devices for measuring and controlling parameters of gaseous and liquid media.

The purpose of the invention is to reduce labor costs and improve the accuracy of measuring the flow rate.

The drawing shows a diagram of the device for implementing the proposed method.

A device for measuring the flow rate of a liquid or gas contains a source of stabilized voltage U, a thermistor 2, three linear resistors 3,4,5 of the measuring bridge, an amplifier 6, a switch 7.

The method is implemented as follows.

Initially, the instrument is calibrated. Key 7 is set to position a. The voltage is chosen such that the current in the circuit, consisting of resistor 3 and thermistor 2, does not cause the latter to self-heat. The thermistor 2 is placed in the liquid or gas under test at the minimum speed and its temperature is determined as the flow temperature by the formula

one

.ptm

(one)

what

Where

RЈO, - thermistor resistance at temp 25

Peru TG 293.15 K; B is a Pbs value;

0

0

five

0

R (t)

R3

 (one

w

 C-

- resist OUT

5 thermistor 2; output voltage

booster. The key 7 is then set to the position §, while the thermistor 2 is turned on in a negative feedback bridge circuit compensating a change in its resistance equal to R (t) -3l-i5j and

R4

The voltage at the output of the amplifier 6 is measured. After that, the switch 7 is switched to the initial position a, the thermistor 2 is placed in the flow with the maximum measured speed v and the flow temperature is determined using formula (1), and then the voltage Un is measured at the output amplifier 6, after switching the key 7 to position b. Calibration coefficient K is determined by the formula:

five

Vr

iVr iV13

-vi (I & tg Thu

(2)

I)

where u

UT --- - reduced value

U

electric output signal during graduation;

fef,

4li LTA

the reduced value of the overheating of the thermistor, equal to the ratio of overheating at maximum to overheating at the minimum measured speed. After graduation, the circuit is reset and the thermoanemometer is ready to measure. Thermistor 2 is introduced into the flow of liquid or gas at an unknown rate, the flow temperature is measured and the value of the output electrical signal. The unknown velocity is determined by the formula

“4 -2.

to N. (TU

k. 1 „tJT

g

AT

one)

(3

where u

ij. Jfc. AT-4y-.

and,

AT

driven values of output signal

thermo-anemometer and overheating temperature of the sensitive element, equal respectively to the ratios of the drop of the load U on the sensitive element and its superheat temperature & T when measuring the flow rate to the initial voltage drop on the sensitive element Ue and its superheating temperature DTfi at the minimum value of the measured flow rate .

The maximum power dissipated by the thermoreistor 2 is ensured by selecting the values of the linear resistors of the bridge circuit from the condition

BSh t

i.

Hhh

The proposed method makes it possible to simplify the process of measuring the flow rate in connection with the absence of the need to adjust the sensitivity of the thermal anemometer each time when the flow temperature changes

16459026

account of this increased measurement.

ten

15

Claims (1)

Claim Method The method for determining the flow rate of a liquid or gas consists in pre-calibrating an overheated sensing element of a hot-wire anemometer at the minimum and maximum flow rates and then recording the output of the hot-wire anemometer, which determines the flow rate, preliminary calibration of the sensing element of the hot-wire anemometer with the minimum value of the flow velocity 20 is carried out at one temperature of the sensitive element overheating, and at the maximum flow rate at another temperature of the sensitive element overheating, and 25, the flow velocity v is determined from the ratio v (-dG - 30 where K is the calibration coefficient; U. JL IT - -&one. AT AT, 35 40 45 given values of the output signal of the hot-wire anemometer and overheating temperature of the sensitive element equal to the ratios of the voltage U on the sensitive element and its overheating temperature DDD when measuring the flow rate to the initial voltage drop of the sensitive element U0 and its superheating temperature D.T0 the minimum value of the measured flow rate.