Chapter 5: Process Interface
54
Valve Drive Level
The position of the valve is given in VALVE_DRIVE_LEVEL. 0% means that the valve is closed
and 100% means that the valve is fully opened (e.g. at the PURGE command).
A typical value under normal operating conditions is 40…60 % with new units. The value depends
on many parameters, e.g. pressure conditions, temperature, contamination, age etc., and may
change also during operation even at the same flow rate.
User Span / Gas Correction
For tuning the flow controller's accuracy the USER_SPAN parameter should be used and for
application of a specific gas the nominal full scale (e.g. N2) may be multiplied by the GCF of the
gas and the parameter FULL_SCALE_RNG may be set with the result. Another option is to set the
parameter GAS_CORRECTION to the GCF of the gas (full functionality only).
User Zero
The parameter USER_ZERO may be set to the flow sensors offset. (See also AUTO ZERO)
Filter
The filter is a single-pole low pass filter. The parameter that the user can adjust is the settling time
of the filter (FILTER_SETTLING). E.g. if a step input (magnitude 100) is applied to the filter with a
settling time of 100 second, the response out of the filter will be within 2% of the final value (98%)
in 100 second. The default value is 0 seconds (no filtering). This filter only influence the output
signal and has no effect on the control circuit.
Gas Tables
Gas tables may be switched off by setting the default table to 15 (i.e. no table is used) and by
selecting the default table. Or by programming a 0 for POINT_NUM (ref. to Calibration Table at
the end of this chapter; function (y=x)) and selecting it. Or by selecting a table with no (zero) points.
A backup of the Gas Tables is generated on Factory Setup. This backup is used for reset the
tables.
Soft Start Rate
A change in the set point is performed in a slope, which is defined by SOFT_START_RATE.
Each controller is factory set to its optimum performance.
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