This field displays the amount of drive in millivolts that it takes to hold the Actual Position at the Target Position while at rest. Ideally this number should be zero if the valve is perfectly nulled.
In RMC100 CPU firmware versions earlier than 19980414, this field is automatically updated toward the Integral Drive when the Actual Position is exactly equal to the Command Position and the speed is zero. However, in later versions this feature was removed in favor of allowing the user to manually update the NULL DRIVE using either the Set Null Drive, Set Null Drive to Integral Drive, or Restore Null Drive commands.
This field is only used in Open Loop Mode. NULL DRIVE is added to the drive output.
Why Bother?
The NULL DRIVE field can be used to null valves and drives. Usually there is a null or offset adjustment on the valve or amplifier that can be adjusted so the NULL DRIVE is 0.
Copyright (c) 1997-2015 by Delta Computer Systems, Inc.