I would like some advice on calibrating a diaphragm differential pressure level gauge
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This post was last edited by hawk1251 on 2015-9-7 at 13:50. I just bought an EJA diaphragm differential pressure level gauge to measure the liquid level in a closed tank; it’s of the capillary type, with the transmitter installed below the lower flange of the tank. The liquid level to be measured is 1.4 m. After installing the transmitter in an insulated box, I placed both the high-pressure diaphragm flange and the low-pressure side of the instrument together, on the flange at the bottom of the tank, and then zeroed the instrument. Next, connect the low-pressure gauge to the flange of the tank and check the displayed value, which is the value a. Is this value a the amount that needs to be transferred? Then, is subtracting the a value from 0-14kp the range that needs to be set? Please advise, experts
The range is the static pressure value of the liquid between the upper and lower flanges (calculated using the formula hρg), while the offset is the static pressure value of the liquid in the capillary between those flanges. It is also possible, after adjusting the transmitter’s range, to install the transmitter and then use an offset or zero-setting potentiometer or a handheld controller to adjust the transmitter to zero when the tank is at its lowest water level; this process completes the adjustment of the transmitter’s offset.
Let me tell you the simplest method: install the level gauge in place, close both the upper and lower isolation valves, and read the current pressure value indicated by the level gauge; it should be a negative value (let’s assume -10 KPA). This value represents the amount of migration. Next, calculate the range of variation for the medium inside the tank. If the medium in the tank is water and the height difference between the upper and lower flanges is 1.4 M, then the pressure variation in the tank will be from 0 to 14 KPA. Therefore, you should set the range to from -10 KPA to 4 KPA
If you install the transmitter below the lower flange, pressure will be applied to the instrument on both the positive and negative sides; however, the pressure on the negative side is greater, and what is detected is still negative pressure. As you said, after installation, the gauge shows a value of A; the height is 1.4 meters. However, it depends on what the medium is – the density needs to be taken into account. If it’s water, then the value will be 14 kPa, as you mentioned. Subtracting the value of A from this gives 20 mA, with the value of A set at 4 mA. The simplest method, as mentioned on the 3rd floor, is that if the range of the instrument chosen happens to be exactly what’s needed, it’s even simpler. For Rosemount transmitters, the zeroing can be done directly by pressing the zero button on the top.
Place the transmitter below the two flanges and secure it. Before putting it into use, check the PV value using the handheld operator; then calculate the pressure at full scale based on the density. The PV value obtained in this step represents the migration amount. The range of the differential pressure is determined based on this