Red Lion TCU - Manual (Page 47)

Valve Position 1 And Valve Position 2 (VPS1, VPS2) (Cont’d)
3) Measure the resistance of the open and closed positions and divide by the
total slidewire resistance to yield percentage values. Directly key-in the
percentage values.
Valve Update Time (VUdt) (Position And Velocity Mode)
The valve update time is the time interval in which the valve position
outputs are updated. The update time may be increased to reduce valve
activity. Valve update times up to 1/10 of the integral time (or process time
constant) may be used with good results. Longer update times may adversely
affect control quality. The update time is variable from 0 to 250 seconds. A
value of zero causes the valve position to be updated at the controller’s scan
rate (10/sec).
Valve Position Deadband (VPdb) (Position Mode)
The difference between the power output and the slidewire valve position
must exceed the deadband in order for the controller to update the valve
position. Normally, the deadband is set to a minimum to compensate for valve
motor overrun and gearing backlash to eliminate hunting. Deadband values
that are too large may result in excessive errors. Values that are too small may
result in excessive hunting. The Output Power Dampening (OPdP) parameter
can also be used to reduce valve activity. Typically set in the range of 1 to 3%.
Valve Fail Time Alarm (VFAL) (Position Mode)
The valve fail time is the maximum time allowed in which the slidewire
feedback signal must match the output power before an error message
appears. If this condition is not met, a valve sentry alarm message appears
(“VALV” in display), indicating a failed valve or failed valve positioner.
Optionally, an alarm can be configured to provide an output event (see
Alarm
Action, page 29). This feature also applies to valve positioning with linear DC
output. The fail time must be set, at a minimum, larger than the Valve Update
Time together with the valve motor transit time. A value of zero disables the
valve fail feature. An active valve fail alarm is silenced in these ways:
1) Set the valve fail time to 0
2) The output power and slidewire signals subsequently agree.
3) Cycle power to the controller.
Valve Motor Open Time And Valve Motor Close Time (VOPt, VCLt)
(Velocity mode)
For velocity mode control, the valve motor open transit time (VOPt) and
valve motor close transit time (VCLt) must be known. In many cases, these
transit times differ from the valve specification. The actual transmit times
under load are normally measured for best results. In some cases, the open and
close times may be different. The transit time range is 1 to 9999 seconds.
Valve Minimum On Time (VONt)(Velocity Mode)
As a result of the pulsed-type algorithm used in velocity mode control, a
minimum on-time pulse threshold is required for proper valve control. The
control does not update the outputs until the calculated on-time pulse exceeds
this value. Normally, set this value to the minimum on-time of the valve
motor. If not given, or otherwise unsuitable, set this value approximately
equal to 2.0 to 5.0% of valve open or valve close time. The minimum on-time
range is 0.1 to 25.0 seconds.
Factory Service Operations Module (9-FS)
The Factory Service Operations are programming functions which are
performed on an infrequent basis. They include: controller calibration, and
reset programming to factory configuration setting. Given the ramifications
of these operations, access to each is protected by an access code number.
Entering code 66 restores all parameters to factory settings, the unit indicates
the operation after the PAR button is pressed, by displaying “rSEt” in the
lower display momentarily. The calibration operations are detailed in
Calibration , page 83.
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