Differential pressure transmitters are used to pressure exerted by a level of water in a vessel. This places great importance on the physical and environmental problems that can affect the accuracy of this indirect measurement.
Errors occur because the DP cell had the sensing line connections reversed.In systems that have high operating pressure but low hydrostatic pressure due to the weight of the fluid, this is easy to occur. This is particularly important for closed tank systems.
Three valve manifolds are provided on DP cells to prevent over-pressuring and aid in the removal of cells for maintenance. Incorrect procedure in establishing 3 valve manifold can effect over-pressuring to the valve.
Sensing line should function correctly. Errors that can occur are:
Measurement reading can be inaccurate when the small diameter lines can become clogged with particulate. Sometimes the problem is first noted as an unusually sluggish response to a predicted change in level.
Draining sensing line:
This error occurs due to the condensation on closed tank dry leg system. As condenstion increases the pressure inside the low pressure impulse line. To prevent this error, condensate most remove regularly. Failure to do so will of course give a low tank level reading.