SU1647276A1 - Method of diagnosis of variable pressure drop flowmeter - Google Patents

Abstract

The invention relates to a flow measurement technique and is intended to assess changes in the metrological characteristic of variable pressure flow meters. The purpose of the invention is to simplify the method of diagnosing variable pressure flow meters. To implement the method, the ratio of the differential pressure across the diaphragm is determined by two different selection methods. The experimentally obtained value of this ratio is compared with the predetermined value and, according to its variation, the test of the flow meter failure. 1il

Description

The invention relates to a flow measurement technique and is intended to assess changes in the metrological characteristic of variable pressure flow meters.

The purpose of the invention is to simplify the method of diagnosing variable pressure flow meters.

The drawing shows the diagnostic node, an explanatory method.

For the implementation of the α-method, the pressure drop across the diaphragm is measured by a known pressure selection method and, at the same time, another pressure selection method. In this case, since the flow rate is the same, it is possible to obtain a generalized characteristic of the flow meter (K) of variable pressure drop from the following relations

QM 0.25 pa g fi D2

(one)

 , 25 rct 2eiytf2D2V2AP2p2, (2)

where QM - mass flow through the constriction device;

a, ar are the flow rates for different methods of selecting pressure drops on a restriction device;

Ј1, Ј2 - correction factors for the expansion of the measured medium (expansion coefficients);

P is the ratio of the diameters of the restriction device d and pipeline D;

APi, APa — pressure drops as the medium flows through the restriction device with different selection methods;

 - medium density corresponding to the selection conditions.

Since the costs in equations (1) and (2) are the same, we can write

APi K (® g &.

"one

(-G Ј1

f

(3)

O - x | Yu VS Oh

When an incompressible fluid flows (pi / 02.61 Ј2), the generalized characteristic of the restriction device K depends only on its geometrical features (the diameter of the opening of the restriction device d, the internal diameter of the pipeline D and their ratio / 3 d / D). The maximum difference in the ratio Ci / cn from the number of Rey-, Nolds in the measuring range of the flow meter does not exceed 0.05%, therefore this change can be neglected.

The change in the value of the characteristic generalized constant, obtained experimentally (Ke) with respect to the calculated value Kp at a fixed ft according to equation (3) in accordance with the condition

Jk

Cr

100% doped (4)

This indicates a metrological failure of the flow meter due to a change in geometry (d or D).

The value of “ODP is assigned depending on the specific technical characteristics of the flow meter and the conditions of its operation, but the minimum of“ OD (min ODOP) ”must not be less than twice the accuracy class of the differential meter.

The diagnostic unit consists of a restricting device 1 (diaphragm), which is installed in the pipeline 2, pressure selection devices 3-6, differential pressure gauge 7, pressure gauge 8, thermometer 9, devices 10 and 11

five

0

five

0

switching (switches) and computing device 12, to the input of the computing device 12 are connected the outputs of the differential pressure gauge 7, the pressure gauge 8, the thermometer 9, and from the output go the control buses to the switches 10 and 11.

The use of the proposed method for diagnosing variable pressure flow meters allows the second narrowing device to be abandoned, to simplify the diagnostic method, to reduce the energy loss of the measured flow, the dimensions of the diagnostic unit.

Claims (1)

Claim method for diagnosing a variable pressure flow meter, comprising measuring a pressure drop by one method of selecting a temperature and pressure at its inlet at a restriction device, characterized in that, in order to simplify the method by diagnosing a restriction orifice directly on the pipeline , the pressure drop across the narrowing hole is additionally measured by another selection method, the ratio of the measured pressure drops is determined and compared with the pressure drop ratio, determined ennyh previously, and on metrological refusal flowmeter is judged by the degree of deviation compared values,