DP cell

A DP cell is a device that measures the differential pressure between two inputs.^[1]

Example:

You have a pressure container where you connect the H-side (high) of the DP-cell. The L-side (low) you leave in the atmosphere (open air). The DP-cell will tell you the pressure in the pressure container relative to atmosphere pressure. Depending on what class the DP-cell is, it will give you feedback with a current signal. Normal in Europe is 4-20 mA,^[2] where 4 is lowest and 20 is highest.

References

1. ^ Bequette, B. Wayne (2003). Process control: modeling, design, and simulation. Prentice Hall. p. 735. ISBN 9780133536409. 
2. ^ Love, Jonathan (2007). Process automation handbook: a guide to theory and practice. Springer. p. 28. ISBN 9781846282812.