A 5 to 20 bar reverse acting proportional pressure controller has an output of 4 to 20 mA. The set point is 11 bar. Determine:
(a) the measured value pressure which gives an output of 15 mA when the proportional band setting of the controller is 40%
(b) the proportional band setting which will give an output of 8 mA when the measured value is 14 bar and the desired value is 11 bar.
The Attempt at a Solution
Can anyone help me with my findings whether i am in the right direction?
Part (b) should be a figure or a %? Thanks
PB = 40% = 0.4
Controller output (Co) = initial control valve + (error x gain)
Gain Comax - Comin / PB = -(20-4) / 0.4= - 40
error e(t) = SP - MP
Controller output = Comax + Gain (SP - MP) 15 = 20 - 40 (11 - MP) MP = 10.9 bar
Controller output = Comax + Gain (SP - MP) 8 = 20 + Gain (11 - 14) Gain = 4
4 = 16 / PB = 4