Fisher DPR900 User Manual page 110

Function
FCODE
OptIon
No Default Selected
Value V&e
PKXXSS
101
Reverse (negative gain) 1 1
TYPO
Direct (posltlve gain)
2
Direct
Pr0CW.S
Increase Increase
Open
ClOSt?
I
1
Use the reverse mode for processes with positive gain; the controller
supplies an output signal with negative gain. In this case, as the pro-
cess value exceeds the setpoint, the output signal decreases.
Use the direct mode for processes with negative gain; the controller
supplies an output signal with positive gain. As the process value
exceeds the setpoint, the output signal increases.
The effect of this FCODE on raise/lower output control is:
n
Direct - as the process value exceeds the setpoint, DO5
conducts, as the process value falls below the setpoint, DO6
conducts.
n
Reversed - as the process value exceeds the setpoint, DO6
conducts, as the process value falls below the setpoint, DO5
conducts.
Example 1 - Pressure Reduction
The requirement in the system shown in the following figure is for the
normally open valve to close if the valve control air pressure fails. The
valve also closes if pressure in the line increases. In either case an
increasing process value must yield a decreasing output from the
controller. The controller must be configured for reversing output.
i/M6 1:DPF#900:9102 May 7991