Operate
6.2 Parameter description
SITRANS VP300 with or without HART
114
Operating Instructions, 03/2011, A5E01258666-03
The flow of the process medium in a pipeline is approximately constant in the case of
continuous processes. If the other conditions do not change, the valve to which the
positioner is connected is always opened or closed by the same amount. If deposits are
produced in the pipeline, the positioner opens the valve a little further in order to keep the
flow constant. If the valve plug is greatly worn or if even parts break off, the positioner closes
the valve in order to keep the flow constant. To establish the travel range in which the
positioner controls the valve, the average reference value is calculated for subsequent
comparison.
The following table contains an overview of the menus and parameters:
3.6.7.1 Activation
3.6.7.5 Threshold 2
3.6.7.2 Time basis
3.6.7.6 Threshold 3
3.6.7.3 State
3.6.7.7 Start
3.6.7.4 Threshold 1
Procedure
1.
Activate the average position value calculation by selecting the "On" setting in the
"Activation" parameter.
2.
Subsequently set the defined duration for the average value of the valve position in the
"Time basis" parameter.
3.
Set the values in the "Thresholds" parameters above which the positioner is to output a
maintenance message. Refer to the description of the 3-stage diagnostics concept in
section "3.6 Settings" (Page 105)
4.
Start the average position value calculation using the "Start" function. Tip: In this
parameter you can also interrupt the average position value calculation for maintenance
purposes.
5.
The "State" parameter indicates the current state of the average position value
calculation.
Result
The positioner now initially starts to determine the reference value of the position for the
duration set in the "Time basis" parameter. The positioner subsequently calculates the mean
value, the so-called average position value, over the same duration. The positioner always
compares the reference position value with the mean position value at the end of a time
interval, and checks whether there is a deviation indicating a changed state of the pipeline or
valve plug.
The current value is displayed in percent in "3.4.14 Reference value of position" (Page 95) or
"3.4.15 Average value of position" (Page 95). If one of the three parameterizable thresholds
exceeds this value during the test, a maintenance message is output by the device.
