• To assure that the positioner is as linear as possible.
• Start at 4mA control signal.
• Give positioner a 4.5mA signal.
• If the positioner moves close to the input signal (as read on the feedback
module) then the
z
ero on positioner is correct. If not then give the positioner
a 4mA signal and adjust the zero
on the positioner so that the positioner is
about to move-gauges are very helpful here.
• Adjusting the zeros so there is movement at 4mA and then, turning the zero
back half a turn.
• PLEASE NOTE THAT ON HEAVIER SET SPRINGS IN THE ACTUATOR IT
MAY TAKE
SOME TIME FOR MOVEMENT TO OCCUR-if the gauges are
reacting the positioner is
responding.
• Give positioner a 20mA signal.
• Give positioner a 19.5mA signal.
• If the positioner moves close to the input signal (as read on the feedback
module) then the
s
pan of the positioner is correct. If not then give the
positioner a 20mA signal and adjust the
span on the positioner so that the
positioner is about to move.
• Adjust the span so there is movement at 20mA then, turning the zero back
half a turn.
• PLEASE NOTE THAT ON SPRING RETURN AND HEAVY SET SPRINGS
CAN CAUSE THE
MOVEMENT IN THE VALVE TO BE DELAYED
SLIGHTLY. BE PATIENT.
• Once these steps have been completed your positioner and feedback
should be very close to
linear in both positioner and feedback.
NOTES:
• Typically if the feedback is way off at 8mA, after
the
zero and span have
been set on the
feedback
it
means that the zero on the positioner is off.
• Typically if the feedback is way off at 16mA, after the zero and span have
been set on the
feedback
it
means that the span on the positioner is off.
• Cam setting-as shown in our manual, it is best to have the small 1/16”
gap between the
roller and the tip of the cam-this helps the unit react
more
quickly
to beginning signal
change.
• On spring return actuators, if “air assist” can be utilized this will generally
improve overall
control and response.
• Valves with relatively high breakaway torques such as butterfly valves and
plug valves can
certainly affect the 4 mA and 20mA calibration and
feedback. If these types of valves are
being used, a judgment by the
customer has to be made to “balance” feedback accuracy
during stroke
and control vs. shutoff or full open position.
V200 Fine Tuning
Positioner Feedback (continued)
Valve Accessories & Controls 200
Jade Park-Chelsea, Al 35043
205-678-0507, fax 0510
www.vacaccessories.com
