SU1323963A1 - Thermoanemometer receiving device - Google Patents

Abstract

The invention relates to a measurement technique and makes it possible to reduce measurement errors by linearizing the output characteristic of the device. The sensing element 5, fixed at the ends of the needle-shaped electrodes 4, is placed in the internal channel of the braking chamber 6. An increase in the measured velocity causes the camera 6 to move, as a result of which the sensitive element 5 appears in a narrow section of the chamber 6. As a result, the local flow rate of the sensitive element 5 increases, resulting in cooling the output characteristic of the thermoanemometer. The internal channel of the spring chamber 6 is shaped according to a specific law. 3 il. 7 If. t30 / h. 5 J CPU2.1: //////////// // /// KALLXXXXXXXXXXX: KXXXXXXXXXX 666 5 X oooooo55 o vwsXXX LHDXXXXXXXXXX with N3 CO X) 05 00

Description

The invention relates to a measurement technique and can be used to measure the velocity of a gas or liquid stream.

The purpose of the invention is to reduce the speed measurement error due to linearization of the output characteristics of the hot-wire anemometer.

FIG. 1 shows a diagram of a receiver of a hot-wire anemometer; in fig. 2 and 3 are diagrams explaining the principle of operation of the device.

The receiving device comprises a holder 1, with the help of which it is introduced into the flow under test, which guides the tube 2 fixedly mounted on the holder. An insulator 3 is inserted inside the guide tube, inside which two needle-shaped electrodes 4 pass. A sensing element 5 is attached to the ends of the electrodes (for example, a bead thermistor). The sensing element is located in the internal channel of the braking chamber 6, which is adapted to move along the guide tube and is supported by the spring 7. The sensing element is inserted into the electric anemometer circuit (not shown) by means of electrodes.

The output characteristic of a thermo-anemometer is a non-linear function known as King’s law. In the device, the sensing element is located inside the braking chamber, in which the local velocity is related to the variable velocity of the undisturbed flow.

The total output characteristic of the hot-wire anemometer, the sensitive element of which is located in this device, must be linear. This is achieved in the device by the fact that the braking chamber is made moving relative to the sensing element, and its internal channel is shaped according to the law determined by the output characteristic of the nonlinearized thermal anemometer, the aerodynamic characteristics of the braking chamber and the spring characteristics.

The law of profiling the internal channel of the braking chamber is as follows.

The output characteristic of the thermoanemometer is expressed by King's law. The linearized characteristic must be

Out-D-V. (1)

To ensure this dependence, the device must provide a link between the local velocity K ,, and the measured velocity V in the form

K .. (2)

The required law of variation of the cross-sectional area of the internal channel can be found from the gas-dynamic flow continuity equation.

SW I / JO / K «, (3)

where Soo- speed undisturbed flow; У „- local speed of flow around the heat-sensitive element;

So-area of the inlet chamber of the brake. After substitution (2) and (3) we get

S (x) S,. (4)

The velocity of the undisturbed flow causing the deceleration chamber to move is found from the equation of the equality of the aerodynamic force

15 g- (0 OL &

 ae-ae.

(five)

where sae is the aerodynamic coefficient

resistance;

Siun is the maximum cross-sectional area of the braking chamber;

p is the density of the medium gas or liquid flow and the force of compression of the spring

.npX. (6)

where K „p - spring stiffness coefficient; X - axial movement (axial size). As a result of the transformations we get

)

thirty .,

I / ;;

(7)

After substitution (7) in (4) we have the final expression

(eight)

S (x)

 r about Km

 The values of n, D, E and c are empirical coefficients or their complexes.

Thus, the proposed device due to the performance of the camera braking

0 moving and with a profiled internal channel allows to obtain an accurate linearization of the output characteristics of the thermoanemometer and thereby reduce the measurement error.

The device works as follows. With an increase in speed of 14, the braking chamber under the influence of aerodynamic forces shifts backward. At the same time, the sensitive element appears in a more narrow section of the braking chamber. The growth of the local velocity occurs due to two factors — the growth of the measured velocity Vea and the narrowing of the local cross section of the internal channel. The linearity of the output characteristic is achieved by compensating for the reduction

5 of the growth of the output characteristic of the hot-wire anemometer due to its cooling (Fig. 2) with a corresponding increase in the growth of the local velocity (Fig. 3).

Claims (1)

Invention Formula The receiving device of the hot-wire anemometer containing the sensitive element mounted in the flow-through chamber made in the form of a guide tube and a braking chamber with an expanding internal channel, characterized in that, in order to reduce errors by linearizing the output characteristics of the thermo-anemometer, the braking chamber is performed: on the ability to move along the guide tube and is spring-loaded, while its internal channel is shaped according to the law defined by 0 /., „With (2К, рХ УЛ-. | L n 5 (X) -C (D; t --- --f Sde rO “t where S (x) is the cross-sectional area internal channel; 5o - the area of the inlet of the internal channel; Sxm - maximum cross-sectional area of the braking chamber CRC - spring stiffness coefficient - aerodynamic coefficient braking chamber resistance; p is the density of the medium; X - axial size; c, l - empirical coefficients. TO m FIG. 2 and.  m Fig.z Ifc 00