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 s lidewire 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,thedeadband isset toaminimumtocompensatefor valve
motor overrun and gearing backlash to eliminate hunting. Deadband values
that aretoo largemayresult in excessiveerrors. Values thatare too small may
resultin excessive hunting.The OutputPower Dampening(OPdP) parameter
canalso beusedtoreducevalve activity.Typicallysetinthe rangeof1to3%.
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, analarm canbe configured to providean output event (seeAlarm
Action,page 29).Thisfeaturealso appliestovalvepositioning withlinearDC
output. The fail time must be set, at a minimum, larger than the Valve Update
Time together with the valve motor transit time. A v alue of zero disables the
valve fail feature. An active valve f ail 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 v alve 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
underloadare normallymeasuredforbestresults. Insomecases,theopenand
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
controldoes notupdate theoutputs untilthe calculatedon-timepulse 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 minimumon-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 code66 restores all parameters to factorysettings, the unitindicates
the operation after the PAR button is pressed, by displaying “rSEt” in the
lower display momentarily. The calibration operations are d etailed in
Calibration, page 83.
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