SU1527533A1 - Method of checking linearity and hysteresis of calibration curve of low absolute pressure gauge - Google Patents

Abstract

The invention relates to a measurement technique and can be used to verify the linearity and hysteresis of the calibration characteristic of low absolute pressure gauges without the use of exemplary measuring instruments. The aim of the invention is to simplify and reduce the test time, control the initial output signal. Through the pumping system 11, through taps 5, 9 and 10, vacuum tank 3 with an adjustable pressure gauge 4, compression device 6 and auxiliary tank 8. Vacuum taps 9 and 10, through gas 2 let gas into tank 3 and into compression device 6 and create pressure corresponding to the I stage. Then the valve 2 is closed, the gas is compressed with the aid of the device 6 and the pressure is recorded with a pressure gauge 4. Then the next pressure stages are created. After reaching the upper limit of measurement of the pressure gauge 4, the pressure is reduced in steps by pumping out the pump. At each stage, the gas in reservoir 3 is expanded by connecting an evacuated reservoir 8. The change in pressure is measured by a pressure gauge 4. According to the results obtained, a conversion factor, nonlinearity, hysteresis and the initial output of the pressure gauge being tested are calculated. 2 Il.

Description

F (/ g /

The invention relates to a control measurement technique and can be used to verify the linearity and hysteresis of the calibration characteristics of low absolute pressure gauges without the use of exemplary measuring instruments.

The aim of the invention is to simplify and shorten the test time, to control the initial output signal of low absolute pressure gauges.

FIG. 1 shows a diagram of an apparatus for carrying out the proposed method; in fig. 2 - construction of the calibration characteristic.

The device comprises a gas inlet system 1, which is connected via valve 2 to tank 3 with a graduated manometer. In addition, through the valve 5, the compression device 6 is connected to the tank, and through the valve 7 - an auxiliary tank 8. The volume of the compression device 6 in the initial state is approximately equal to the volume of the tank 8. Tanks 3 and 8 are connected to the pumping system 11 via valves 9 and 10.

The verification method is as follows.

During the forward calibration in the tank 3 with the calibrated pressure gauge k and the compression device 6 from the pressure source 1, fixed pressure values are created that are uniformly distributed over the measurement range of the pressure gauge from the initial value to the nominal value. Pressure setting is performed on the output signal of a calibrated gauge. When the required pressure is reached at each fixed point, compress the device 6 of the compression and record the increment of the signal of the pressure gauge 4.

The conversion factor for the i-th point of the calibration characteristic Kjj (Fig. 2) is calculated using experimental data using the formula

X 1 iii.-i-.

 i 111 o

; i)

derived from ratios

P, (. K X., „- XJ, (2) Rig K X ,, - XJ-, (3)

Р, (11 V Р, „. (V - V,), (C)

Q

five

0 5

0

5 0 5

0

five

where X. is the output signal of the pressure gauge 4 after compressing the compression device 6;

Xj ,, is the output signal of the pressure gauge when pressure is applied, corresponding to the i-th calibration point and the initial position of the compression device 6;

X - the initial output signal of the gauge A;

R, - (o.

 - pressures corresponding to the output signals of the manomet-Pa X ((, | and X, (,; K - nominal coefficient

transformations;

V is the total volume of the tank 3 and the compression device;

V is the volume of the device 6 compression.

From the expression (k) it follows P, - (U V

 const,

R; s V - VK

from (2) and (3) in view of (4)

X, (1) - Ho ,, G - y-const K ,. .

 1 (1)

For the implementation of the forward course of calibration, the following operations are performed. Using a pumping system 11, vacuum is applied through vacuum valves 9, 10 and 5 to tank 3 with a calibrated manometer, compression device 6 and auxiliary tank 8. Close valves 9 and 10 and create gas through valve 2 through the system 3 6 compression pressure corresponding to the 1st graduation point. Pressure setting is carried out as indicated by a pressure gauge. Close valve 2, compress compression device 6 and record the pressure increment in tank 3 with a pressure gauge 4. Close valve 5, bring the compression device to its initial position. Repeat the operation (except for vacuuming) for all points of the calibration characteristic. After creating in the tank 3 with a pressure gauge corresponding to the upper limit of measurement

gauge 4, the course of calibration is complete.

To perform the reverse calibration, the following operations are performed. The crane 7 is connected to the tank 3 by the auxiliary evacuated tank 8. They record the change (decrease) in the pressure in the 5th point on the manometer. The tank 8 is disconnected from the tank 3 and vacuum is evacuated by the exhaust system 11 through the valve 10. The latter is closed. The valve 9 is opened and, using the pumping system 11, a pressure gauge in the tank 3 is set to the pressure corresponding to the (n-1) -th calibration point. Close the valve 9.

These operations are repeated for the remaining points of the calibration characteristic, thereby performing a reverse calibration course.

The calculation of conversion factors for all points of the calibration characteristic during the reverse calibration course is performed similarly.

The adjustment of the position on the calibration characteristic of the point X, jco-corresponding to the initial signal of the manometer and used in the calculations, is performed as follows.

A pressure P is created in the tank 3 and the device 6 of the compression, which is fixed by reading of the pressure gauge. Compress the compression device and re-fix the pressure of the pressure gauge AR Calculate the initial value of the output signal of the pressure gauge A according to the formula

WITH/("

X „X (C, + 1) - obtained from the obvious ratios P, K (X - Ho) -,

to S1

- PV ,,, -

PX-V PX („

(V - Vj;

WITH,

 VK V

where V is the volume of the tank 3 and the device 6 compression; V is the volume of the compression device. Using the data of calculating the conversion factors for forward and reverse calibration steps, the initial output signal of the manometer, the methods of mathematical statistics determine the average value of the conversion coefficient, the nonlinearity of the calibration characteristic and the hysteresis.

When using the proposed

5 of the method simplifies and improves the performance of determining linearity and hysteresis, due to the fact that there is no need for carrying out preliminary complex calculations and

0 operations that provide an increment and a decrease in pressure in equal steps in the forward and backward strokes of calibration, the time for setting the specified pressures is reduced due to simplification

5, the vacuum system is improved, the determination accuracy is improved and the initial output signal can be monitored, there is no need to use linearity to determine

Claims (1)

0 and hysteresis of exemplary gauges. Invention Formula The method of checking the linearity and hysteresis of the calibration characteristics of low absolute pressure gauges by pre-vacuuming the tank with a calibrated gauge, increasing the pressure in it by gas inlet steps to the airflow limit of the gauge, subsequent pressure reduction by pumping gas steps to the lower limit of measurement and measuring pressure at each stage with a measurable manometer, characterized in that, in order to simplify and shorten the test time, as well as to control the initial In the output signal, at each stage, gas is compressed with increasing pressure, and at each stage, gas is expanded with decreasing pressure. five 0 Pill} t (l) ) Xi {2) jig