Instrumentation Specialist Question:

A) An offset is difference between a desired value and an actual value. The phenomenon of a dependent variable assuming a different set of values when the corresponding independent variable is increasing than when it is decreasing is known as hysteresis.
B) Offset is fixed bias from desired value. Hysterisis is difference between set and reset.
“ Pressure switch with setting of 0.5 kg/cm2 (head pressure included) was found in calibration report . What is the significance of head pressure?
Head pressure refers to the pressure exerted by fluid inside the impulse pipe connecting the pressure switch to the vessel. This pressure acts in addition to the actual process pressure in the vessel. Pressure acting on switch = process pressure + head pressure.