In this paper, an electric differential pressure transmitter is an example of analog validification of differential pressure level gauges. This method is simple, and intuitive, especially for beginners to understand the working principle of differential pressure, and can also apply in teaching. In addition, it can also solve the calibration low-volume water position (such as 2 kPa of the boiler steering), it is difficult to find the problem of standard tables.
According to fluid static, the level of liquid level can be judged by the static pressure of the subject liquid column. The static pressure can be detected by a meter such as a differential pressure gauge. The liquid level and differential pressure have the following relationship:
H = △ p / ρ
Where: H - liquid level height (mm);
△ p - Differential pressure (PA);
ρ - Liquid density (g / cm3).
When the liquid density is constant, the liquid level height can be known if the differential pressure is measured, and the liquid volume is independent, or the liquid height is known, and the differential pressure is known, that is, ΔP = ρH. The analog validation is based on the above principles. Now use the check water level as an example, introduce the specific method, the calibration device and the wiring are shown in the figure:
The calibration pressure transmitter and the reading scale (the can be used as a rod size or U-shaped pressure measurement ruler) is perpendicularly fixed. Two manual gas analyzers are prepared, and the rubber pipe is received to the three-valve set of the differential pressure transmitter, in order to make the reading convenient and accurate, a movable bracket can be placed to place a level bottle. The three valves of the three-valve group are all open, and the exhaust risks of the upper end of the differential pressure transmitter are geared, and the water is irradiated from any level of the bottle; to be overflow from the exhaust screw; after the air bubble, tighten the exhaust Screw. And the water surface of the two level bottles remains half a bottle, set the two-level bottle in the same height (usually the "0" scale of the ruler), and balance the water surface of the two bottles. After the electricity is preheated, check the zero position of the differential pressure transmitter, which does not match the zero potentiometer of the fracture, so that the output is 4mA. After adjusting the zero, turn off the balance valve. At this point, the level bottle connected to the transmitter H is raised to change the vertical distance of the water surface of the two level bottles, and make it the maximum measurement range, see if the output of the transmitter is 20mA, otherwise the modulation potentiometer, The output is 20 mA. After the zero and full-scale request, change the water surface vertical distance of the level bottle to see if the intermediate range is extremely deviation. Migration adjustment work is made normally. Positive, negative migration adjustment view of the differential pressure transmitter, usually: The level of the liquid level is measured by the level of the mouth, and the liquid level of the closed container is negatively migrated. Just involving which level of the bottle is raised. Should the level bottle lifts when migration? Should be determined according to the positive and negative movement. However, it is all as a reference point with a level of water, and the other level bottle is moved up and down, and the water surface distance of the two level bottles (reading from the ruler), that is, the liquid level H value, that is, the differential pressure △ P value. The level of movement of the movement is moved to the highest point (or lowest point) according to the meter range, and then the displacement potentiometer is adjusted.
When measuring the water level under other liquids and conditions, the quantities should be calculated according to its actual density.
Responsible Editor: PJ, Reading
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