A question regarding the calculation of level transmitters
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The level transmitter in our plant has a measurement range of 0–9.965 kp, while on the central DCS system the range is -16.521 to -26.486 kp. The value displayed on the transmitter at the site was -21.23 kp, which corresponds to 36%. Later, I calculated it myself and found that at a pressure of -21.23 kp, the value was 52.7%, which is different from the percentage shown by the transmitter. I’m very frustrated; I don’t know where my mistake lies – maybe it’s my algorithm that’s incorrect. I hope everyone can tell me the correct way to calculate it. Thank you!
Reply to 1# sky1liner7: You’re right with your calculation; maybe you misread the signs on site. Hang up 375 and check the measurement range.
Is the range on the DCS -16.521 to -26.486 kp? I guess you should at least be an integer, right? Even without a decimal point, it’s pretty much the same, right? Also, the range is 0-9.965 kp. Is this the instrument built into the equipment by the manufacturer? It seems like you might have misseen it, right? I hope to get an answer.
It seems like you’re making it too complicated. Generally, the liquid level on the DCS is displayed as 0-100%, with the input signal being in the 4-20 mA DC range. All that is needed is to set the zero point and range of the field liquid level transmitter (by calculating the transmitter’s measurement range based on the density of the medium and the measurement height)
Is the device being measured vacuum?
Reply to 3# Ah Hai: It’s not as you think. The liquid level value may be an integer, but the differential pressure calculated from the liquid level is unlikely to be an integer, unless by pure chance. For example, in the case of a liquid level ranging from 0 to 1000 mm, with the medium being diesel and a density of 0.8675, the range for the differential pressure will be 0 to 8.675 kPa. To make this value an integer, some adjustment is needed, which is quite difficult.
Is the range of 0-9.965 KP on your gauge indicated by a reading of 375? Since it’s all -21.23 KP, that exceeds the range of the gauge; the gauge becomes unstable, so how can it display the liquid level? The 52.7% you calculated is based on the range of the central DCS system; of course, it differs from what the gauge shows. If you change the range on the gauge to match that of the DCS, then it will display the value you calculated
This is complete nonsense; how could such a setting exist? At least the on-site display should be the same as the remote display, right? Or you can just use a percentage – if these two figures don’t match, do you still need to do calculations to determine accuracy? I’m fainting
I think it needs to be clarified: 1. Is the transmitter for measuring the liquid level a differential pressure type? For example, double flange or single flange? If it is a single-flange type, it should be used on open containers. 2. Where did you see the range of 0-9.965 KPa? If it is set this way on the transmitter, the numbers you see will definitely be incorrect. It is clearly beyond the measurement range. 3. Is it still necessary to set the range on the DCS lower-level unit? Neither the central control systems nor the Ganga systems we use currently have such a setting; generally, 0~100% corresponds to 4~20MA, and it’s sufficient to make the settings on the local gauge. If that were the case, every time I adjusted the instrument parameters, even just adjusting the zero point, I would have to modify the lower-level device and then perform a download, which is not practical. 4. As for calculating the liquid level differential pressure, this is taught in junior high school; one just needs to disconnect the instrument’s vent, set the range, automatically adjust the zero point, and then it’s ready for use. It’s not as complicated as you think.
The liquid level is generally controlled between 0-100% at the central control system; based on the readings from the gauge, it seems that the level has exceeded the specified range. Therefore, it’s necessary to check both the installation and the settings of the gauge to determine where the problem lies
I think it’s like this: the range of the field meter you mentioned is the range at the time of manufacturing, while we know that the operating range can be modified using a handheld device; thus, it’s possible to check whether the system’s range matches the field meter’s range.