Analog calibration method for differential pressure level gauges - News - Global IC Trade Starts Here Free Join

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This paper takes the electric differential pressure transmitter as an example to introduce a simulation verification method of differential pressure level gauge. This method is simple and intuitive, and it is very helpful for beginners to understand the working principle of differential pressure measurement of liquid level, and it can also be applied in teaching. In addition, it can solve the problem of finding the standard meter when verifying the low-range water level gauge (such as the range of the boiler drum water level is only about 2KPa).
According to the hydrostatics, the level of the liquid level can be judged from the static pressure of the liquid column of the object to be measured. 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);
ΔP——differential pressure (Pa);
Ρ—liquid density (g/cm3).
When the liquid density is constant, the liquid level is known by measuring the differential pressure, and the differential pressure is known regardless of the liquid volume, that is, ΔP = ρH. The analog calibration method is based on the above principle. Now take the calibration water level gauge as an example, introduce the specific method, the calibration device and wiring are as shown:

The differential pressure transmitter and the reading scale (available steel ruler or U-shaped pressure gauge scale) are fixed vertically. Prepare the leveling bottles for the two manual gas analyzers, and connect them to the three-valve valve connector of the differential pressure transmitter with rubber hoses. To make the readings convenient and accurate, you can make a movable bracket to place the leveling bottle. Open all three valves of the three-valve group, loosen the exhaust screw at the upper end of the differential pressure transmitter, and fill the water from any level bottle; wait for the water to overflow from the exhaust screw; after exhausting the air bubbles, tighten the exhaust Screw. Keep the water level of the two level bottles to about half a bottle, and place the two level bottles at the same height (usually set to the “0” scale of the scale) to balance the water surface of the two bottles. After the power is warmed up, check the zero position of the differential pressure transmitter. When the discrepancies are not met, adjust the zero potentiometer of the transmitter to make the output 4 mA. After adjusting the zero position, close the balance valve. At this time, raise the level bottle connected to the H end of the transmitter to change the vertical distance of the water level of the two level bottles, and make it the maximum measurement range. See if the output of the transmitter is 20 mA, otherwise adjust the range potentiometer. Make the output 20mA. After the zero and full scale meet the requirements, change the vertical distance of the water level of the level bottle to see if the middle range is out of tolerance. After the normal operation, the migration adjustment work is performed. The adjustment of the positive and negative migration depends on the use of the parallax pressure transmitter. Normally, the liquid level of the open container is measured for positive migration, and the liquid level of the closed container is measured for negative migration. It only involves the question of raising the level bottle. Should the level bottle rise and fall during the migration? It should be determined according to the positive and negative migration conditions. However, the water level of one level bottle is used as a reference point, and the other level bottle is moved up and down along the scale. The water surface distance of the two level bottles (which can be read from the scale) is the liquid level H value, that is, the differential pressure △ P value. Move the moving level bottle to the highest point (or lowest point) according to the meter range, and then adjust the potentiometer to make it meet the requirements.
When measuring the water level under other liquids and working conditions, the range should be adjusted according to its actual density.