Is the negative migration of the hydrostatic level gauge too large and the gauge needs to be changed?

The measurement principle of the hydrostatic level gauge is to measure the liquid level based on the relationship between the static pressure and density of the liquid. When the liquid height changes, the corresponding static pressure will also change, thereby obtaining information about the liquid level. The "negative migration" mentioned in your question generally refers to shifting the starting point (zero point) of measurement to the negative direction of the measurement range. In essence, this is to expand the measurement range or change the starting point of measurement. In your case, what you need to measure is the lower half of the level, which is the range of 0-2 meters, but your level gauge does have a range of 0-4 meters. Therefore, you need to perform negative migration on the liquid level gauge and move the starting point of measurement to 2 meters, so that you can measure the liquid level from 0 to 2 meters. The reason why the manufacturer said "the negative migration is too large and needs to be replaced" may be because the range of negative migration exceeds the limit that the level gauge can withstand. It should be known that large negative migration will also increase measurement errors. On the other hand, if the range of negative migration is too large, it may prevent the level gauge from working properly and may even damage the level gauge. It is recommended that you communicate with the manufacturer in detail to understand the specific reasons for replacement, or find a professional instrument maintenance personnel to check. If necessary, it may be necessary to replace the level gauge with one that better suits your needs. .

The distance between the upper and lower flanges is 4 meters = 40KPa, and the maximum range of your meter is 32KPa, and its migration amount is only -32KPa, so the meter needs to be replaced.

How is this migration amount calculated? I always feel that if the pressure difference between the upper flange and the two flanges is not more than 2 meters, it will be 20kpa. It should not affect the use.

　The transmitter with a maximum range of 32kPa is not enough to move 4 meters. 　The complete hydrostatic method liquid level measurement is as shown below, if: The density of the red medium in the positive pressure tube is ρ1, and the density of the blue medium in the negative pressure tube is ρ2. Then the migration amount required by the transmitter is: Migration amount = h1×ρ1-h2×ρ2 For a double-flange transmitter, the two capillary tubes can be regarded as pressure tubes, and the density of the filling fluid is consistent with both ρ0. When the installation position changes, the liquid column pressures of the two pressure tubes offset each other in the direction, so there is always: Migration amount = (h1-h2)ρ0. 　Due to structural reasons, the migration amount of the double-flange transmitter usually cannot exceed 100% of the maximum range (±32kPa). If the above (h1-h2) = -4000mm, and ρ0>0.8, the required migration amount will exceed -32kPa. 　There is a problem here. The maximum migration amount allowed by the double flange transmitter is different from the products of different manufacturers. The reason for determining the migration amount is actually that the pressure of h1-h2 may cause the diaphragm to move to the "top dead" position, so it is generally considered that it cannot exceed 100% of the maximum range. In fact, many transmitters are not subject to this restriction. ； 　in addition: What is the maximum range of your transmitter? Many times the maximum range of the transmitter will be larger than the calibrated range. At this time, the range that can be migrated will be larger than the marked range.

You bought an FKD double-flange differential pressure transmitter. The capillary tube is 5 meters. Is the distance between the two flanges on your device 4 meters?

The complete model number is in your photo.: FKD6Y3VC-LUSBY-Y0C8W。 What I need to know is the distance between the two flanges of your equipment and the density of the measured medium before I can calculate the migration.

The two flanges are 4.1 meters, and the medium density is about 1000-1100kg/m3. Please give me some guidance.

Could it be that we just made it a little bigger? There is another story. When I signed the contract, it actually said -32~32Kpa. Later, I felt that there was no need to change it. Is it okay to stick to the original one?

If we use process control to only allow a 4-meter water tank to have a water level of 2 meters, can we still use it without having to withdraw the watch and modify it?