RESET (INTEGRAL) CONTROL SYSTEMS
Process Controls
Figure 20 Integral Flow Rate Controller
Initially, the system is set up on an anticipated flow demand of 50 gpm, which corresponds to
a control valve opening of 50%. With the setpoint equal to 50 gpm and the actual flow measured
at 50 gpm, a zero error signal is sent to the input of the integral controller. The controller output
is initially set for a 50%, or 9 psi, output to position the 6-in control valve to a position of 3 in
open. The output rate of change of this integral controller is given by:
Output rate of change = Integral constant x % Error
If the measured variable decreases from its initial value of 50 gpm to a new value of 45 gpm,
as seen in Figure 21, a positive error of 5% is produced and applied to the input of the integral
controller. The controller has a constant of 0.1 seconds-1, so the controller output rate of change
is 0.5% per second.
IC-07
Page 30
Rev. 0
