Precision empty box pressure gaugeIt is an atmospheric pressure measuring instrument that uses deformable elements as induction. It has the advantages of easy portability, accurate measurement, wide pressure measurement range, easy use and maintenance, and no mercury pollution.
Precision empty box pressure gaugeRevision method for temperature and scale:
1、 Temperature correction
At the same atmospheric pressure, when the temperature of the instrument changes, the elasticity of its spring pin also changes, causing the pointer of the empty box pressure gauge to indicate different pressure values. As the temperature increases, the metal elasticity weakens, the diaphragm box compresses, and the reading is higher; When the temperature decreases, the elasticity of the membrane box increases and the indication is low. In order to reduce the impact of temperature on instrument readings, compensation for temperature changes is considered when manufacturing empty box pressure gauges. At present, domestically produced empty box pressure gauges generally use gas compensation method, which means leaving an appropriate amount of gas in the empty box. When the temperature rises, the increase in gas tension inside the box causes the empty box to stretch upwards, partially offsetting the compression effect caused by weakened elasticity. When the temperature decreases, it has the opposite effect. Although this is the case, the effect of temperature cannot be completely eliminated, therefore, the reading obtained from the empty box pressure gauge must also be temperature corrected. When making corrections, the temperature correction value is obtained by multiplying the temperature coefficient listed on the calibration certificate by the current temperature shown on the temperature gauge attached to the empty box pressure gauge.
2、 Scale correction
The response of an empty box pressure gauge to pressure changes varies in different parts of the scale. The instrument was calibrated before leaving the factory, and the calibration results were listed on the factory calibration certificate for correction during observation.
3、 Supplementary correction
The elasticity of the empty box pressure gauge and the condition of other components will vary over time, especially when the instrument is subjected to severe vibrations, and this variation is more significant. At the same time, due to the inaccuracy of adjusting the pointer, it is necessary to supplement and correct the reading shown on the empty box pressure gauge. On the calibration certificate of the instrument, there is a supplementary correction value listed, which has a validity period of 6 months. If it exceeds this period or encounters special circumstances, it should be re calibrated and the new supplementary correction value and calibration date should be filled in on the calibration certificate.
4、 Height correction
The thickness of air varies at different altitudes above sea level, resulting in different measured air pressure. The higher the altitude above sea level, the lower the air pressure. In order to compare the atmospheric pressure levels in different regions, it is necessary to correct the atmospheric pressure measured in each region to the sea level. This correction is called altitude difference or altitude correction, also known as sea level correction.
In order to obtain accurate calibration results, when comparing the empty box pressure gauge with the mercury pressure gauge, the supplementary correction value can be calculated according to the following method:
1. The empty box pressure gauge should be placed in the same room as the mercury pressure gauge, as close as possible, and can only be compared after stabilizing for about 3 hours.
2. The number of days for comparison should not be less than 5 days, and two or more comparisons can be conducted per day, but the interval between the two comparisons should not be less than 8 hours.
3. The supplementary correction value measurement method is to compare the reading of the empty box pressure gauge with the reading of the mercury pressure gauge under natural atmospheric pressure conditions.
4. Each time, two readings should be taken, and the order of the two readings should be reversed, that is, the mercury pressure gauge should be read first, followed by the empty box pressure gauge, and the second reading should be taken every 10 to 15 minutes. The second time is to read the empty box pressure gauge first, and then read the mercury pressure gauge.
When comparing readings, the air pressure should be stable. If the change in air pressure between two readings exceeds 8 millimeters, no comparison should be made.
6. The reading of the mercury pressure gauge should be corrected to "local station pressure". The reading of the empty box pressure gauge should be calibrated and temperature corrected, and then the difference between the two corrected pressure values should be calculated one by one. The new supplementary correction value is obtained by averaging the 10 differences. If the supplementary correction value is greater than 4 millimeters, it should be stopped from use and sent for maintenance. The so-called 'local air pressure' refers to the reading of the mercury pressure gauge that has been corrected by instrument difference, temperature correction, and gravity difference correction. Its value can represent the air pressure value of the local station at that time, hence it is called 'local air pressure'.
By the way, it should be pointed out that every time the empty box pressure gauge is observed, the glass surface or instrument housing should be lightly tapped with fingers to eliminate frictional resistance in the transmission mechanism and ensure accurate readings. In addition, the manual needle installed on the glass surface should be rotated in a timely manner to align with the current air pressure indicator, so as to observe the changes in air pressure in the future. When the empty box pressure gauge is not in use, it should be properly stored and not placed randomly. It should be placed in a dry, collision resistant, and temperature stable place.
All the components of the empty box pressure gauge are installed inside the shell, with a small hole on the side of the shell and an adjusting screw inside. If this screw is turned, it will cause changes in the shape and mechanical parts of the empty box, and it must be rechecked before it can be used. Therefore, this screw can only be turned during inspection by the factory or inspection department, and should not be tampered with casually.