SU821958A1 - Pneumatic thermometer - Google Patents

Description

(54) PNEUMATIC THERMOMETER

one

This invention relates to thermometry and can be used in various industries to automatically measure the temperature of gas streams.

A pneumatic thermometer containing a power source and a choke bridge converter is known.

AND.

However, this device does not have the required measurement accuracy due to the presence of aerosols in the measured gas flow, which are deposited in the channels of the throttle elements.

The closest to the technical essence of the proposed is a pneumatic thermometer containing a SOURCE, a power supply equipped with a gearbox and a filter, a throttle bridge converter, the working branch of which includes a throttle temperature converter and an auxiliary throttle having the same channel diameters, and the comparative branch is a laminar throttle moreover, the inter-throttle chambers of the bridge converter are connected to the inputs of the amplifier, the output of which is connected to the platoon of the repeater connected to one Oriental device.

moreover, a series of constant and variable chokes is connected to the output of the reducer, the outputs of which are connected to the third and fourth inputs of the amplifier, and the output of one of the constant chokes is connected to the output of the setpoint 2.

However, in this device, the temperature of the monitored medium is measured with a large error of at least 6% of the maximum scale pressure of the indicating instrument. The low measurement accuracy is due to deviations in the homogeneity of the composition of the inert gas feeding the measurement circuit and the inability to maintain a stable temperature in the thermostat due to the presence of a temperature gradient between the throttle of the bridge converter.

The purpose of the invention is to improve the measurement accuracy.

To achieve this goal, an additional power source and a control choke are included in the device, which is connected to the comparative branch of the bridge converter, each of whose branches is connected separately to the power sources.

The ratio of the lengths of the channels of the auxiliary throttle and the throttle transducer is within, 7-3.0.

The drawing shows the scheme of the device.

The proposed device includes a power source 1, a constant choke 2, a throttle temperature converter 3, a measured medium 4, a regulating choke 5, a constant choke 6, an additional power source 7, an amplifier 8., a constant choke 9, an air sensor 10, a constant choke 11, adjustable choke 12, constant choke 13, repeater 14, secondary device (pressure gauge) 15 power supply 16, filter 17, gearbox 18, pressure bridge supply PO, bridge pressure, P and P in inter-throttle chambers of a bridge throttle converter

 The device works as follows.

The measured temperature causes an imbalance in the bridge converter formed by four 2–2 chokes. The measured differential pressure of a bridge circuit is a function of several independent variables.

. (tn, tj-, Po, d, e), where AP is the measured pressure drop

pavement with; hema; P is the pressure in the inter-throttling chamber of the working branch of the bridge (chokes 2 and 3); Р „- pressure in inter-throttled

the chamber of the working branch of the bridge; tj, is the measured temperature; t is the ambient temperature;

d is the diameter of the throttling channel 6 - throttle length. When the measured temperature changes, the viscosity of the air flowing through the channel of the throttle 3 changes, which causes a change in the pressure drop across it and leads to a change in pressure in the inter-throttling chamber of the working branch of the bridge, and therefore to imbalance of the bridge circuit.

Let us consider in more detail the effect of a change in the measured temperature on a change in the pressure value in the inter-throttling chamber of the working branch of the bridge.

In stationary mode, if the measured temperature and ambient temperature are equal according to the Poiseyl law, the working branch of the bridge can be written

d h 4

..

/1Р-)-1Р.-Р.Ь ,,

where | li and p are, respectively, the dynamic viscosity coefficient and the density of air flowing through the throttles;

PQ - branch feed pressure

the bridge;

PQ is atmospheric pressure. If the measured temperature is higher than the ambient temperature, then when setting the mode, equation (1) takes the form

14 14 1

lf. {p-P - - - (pp

-ju-l o, ju- (i a 2)

where fU and p are respectively the dynamic viscosity and density in the spirit of the S channel of the primary converter 3 at the new value of the measured temperature;

P is the pressure in the inter-throttling chamber corresponding to the new value of the measured temperature.

New pressure value in the inter-throttling chamber will be obtained by solving equation (2) with respect to PJ

p - 4

 .5зрр (3)

4-1-:

.

The pressure increment in the inter-throat chamber of the working branch of the bridge is equal to

p -; - v-io-) i ,, ,,,

but

Where

fu.p

Therefore, the DS depends on the measured temperature in terms of a. The imbalance of the bridge circuit is determined by the supply pressure PQ, which must be stabilized. The pressures P and Formed in the inter-throttle flow chambers formed by the throttle elements 2-3 and 6-5 are fed to the 4-input amplifier 8. The power supply of the lower coil of the amplifier 8 is carried out from the element of constant air flow 16. To create the initial output pressure of the thermometer The setting device 10 is used. The output pressure of the amplifier 8 is amplified by a still powerful repeater 6 and is directed to a second device 15, which can be used with a conventional manometer. An experimental study of the operation of the thermometer shows that in order to ensure a linear dependence of the increment of pressure difference in the center of the throttle chamber of the working branch of the bridge from the measured temperature, it is necessary that the ratio of the lengths of the secondary throttle and throttle converter with identical channel diameters be within 2.7-3.0 .

Introduction to the proposed thermometer regulating membrane throttle 5 reduces several times the imbalance of the bridge converter, due to

Claims (1)

Claim 1. A pneumatic thermometer containing a power source, equipped with a gearbox and a filter, a throttle bridge converter, in-. the lateral branch of which includes a temperature throttle converter and an auxiliary choke having the same channel diameters, and a laminar throttle in the comparative branch, the inter-throttle chambers of the bridge converter are connected to the inputs of the amplifier, the output of which is connected to the input of the repeater connected to the secondary device, and to the output of the gearbox connected a series of constant and variable chokes, the outputs of which are connected to the third and fourth inputs of the amplifier, 10 '