measurement & control

[jimmy56]

1) Is it possible to calibrate a dp transmitter in workshop below its minimum span limit. We purchased a transmitter range LRL = -10kpa and URL 10 kpa. Minimum span limit given on Tr was 5 kpa. We adjusted it to 2.5 kpa ( forgotten span limit) by applying pressure on + leg and leaving -leg in area. But when installed in field it started giving random values. Why ?<br>
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2) How I can calculate minimum plate thickness for flow element ?<br>
3) Is someone help me to calculate dp for elbow type flow measurement?

 

[fcx]

Many of the new digital transmitters can be calibrated above the cell span limits and below the zero limit. However, the cell mapping for the electronics can not get a correct count vs. input and drifting as you have experienced is the result. The only cure is to purchase the correct cell for the ranges desired. You used to be able to do this with many of the old analog electronic transmitters and they appeared to work. In reality they were not accurate or repeatable when this was done.