I’m a beginner in instrumentation; I seek advice from experts everywhere

First of all, the amount of migration you mentioned is also related to the location of your transmitter; the range can be determined easily, which is density × G × height (1000 mm)

There must be a connection between them; if the position is uncertain, how can the amount of migration be calculated? Since this problem involves calculating negative migration, it must refer to a double-flange differential pressure level gauge with negative migration

Please tell me the location of your transmitter, so that the migration amount can be calculated.

Hehe, I just want to say that it’s just a set of questions; I struggled for ages but still couldn’t figure it out

If it is just one question, it is generally assumed that the transmitter and the pressure tapping are at the same level. The migration amount is naturally the pressure in the negative-pressure capillary, which is also the lower limit of the measurement range.

They asked you to do the calculations, but after talking for a long time you still didn’t give a result. Let me tell you: given that \"the maximum change in the liquid level of a certain tank is 1000 mm, the density of the medium is 1.0 g/cm3, and the density of the liquid filling the capillaries is 0.95 g/cm3, please calculate the amount of negative migration as well as the range and measurement limits in kPa,\" it can be determined that 1) the density of the liquid stored in that tank is 1000 Kg/m3, which means it’s water. Damn. . . . 2. Assume that the H end of the transmitter is installed at the bottom, while the L end can be installed at any point between 5 and 10 meters. The density of the capillary tube is 950 Kg/m3 (of course, in practice it’s not possible to install it too high; firstly, there aren’t capillary tubes long enough for that, and secondly, moving so many transmitters would be impractical – this is just an assumption). In that case, we can carry out the following calculations: 1. Negative migration = ρ_capillary * g * h (5–10) = 950 * 10 * 5 or 950 * 10 * 10 = 47.5 Kpa or 95 Kpa. 2. For calculating the range, the most important factor is the height difference between the positive and negative sides of the transmitter. The maximum range of a double-flange level gauge cannot exceed this height difference. We’ll use a value of 10 for this purpose: ρ_water * g * h = 1000 * 10 * 10 = 100 Kpa. 3. The measurement range is from the negative migration value to the maximum range, which in this case is from -95 Kpa to 100 Kpa. 4. After installation, first close the valves, allow atmospheric pressure to equalize the readings, then set the transmitter’s range to the value calculated in step 3. Tighten the flanges and open the valves. Incidentally, the calculations above are merely theoretical values; in practice, it’s not possible to do this. If storing water, use a single-flange gauge – no need for migration adjustments, just set the range and zero the gauge directly. If storing hazardous materials that require sealed containers, double-flange gauges should be used; excessive negative migration is unlikely to occur. The reason is that double-flange level gauges do not have such long capillaries. Moreover, if the transmitter experiences significant migration, it is necessary to consider what the measurement range specified by the manufacturer is. Excessive migration will result in inaccurate readings from the transmitter. I appreciate it if you can point out any issues so that we can learn together. Thank you

Negative migration = ρ·capillary·gh (5–10) = 950*10*5, or 950*10*10 = 47.5 KPa or 95 KPa. I don’t understand what the *10* in this calculation means; could you please explain it? Thank you

The 10 in the middle represents the acceleration due to gravity g = 10 N/Kg (strictly speaking, it should be 9.8)

Here, the gravity coefficient is g=9.8 Newtons/kg, and it serves as a constant when calculating pressure. The value of gravitational acceleration that I just mentioned is g=9.8 m/s2; the numbers are the same, but the concepts are confused. I haven’t thought about this for many years now; it’s simply used for calculations. I’m sorry