Flowserve 3400IQ Digital Positioner - Manual (Page 74)

Logix 3400IQ Digital Positioner FCD LGENIM3401-00 – 06/06
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13 Frequently Asked Questions
Q: I set the Final Value Cutoff Low at 5 percent. How will the positioner operate?
A: Assume that the present command signal is at 50 percent. If the command signal is decreased,
the positioner will follow the command until it reaches 5 percent. At 5 percent, the spool will be
driven fully open or fully closed, depending on the air action of the valve, in order to provide full
actuator saturation and tight shutoff. The positioner will maintain full saturation below 5 percent
command signal. As the command increases, the positioner will remain saturated until the command
reaches 6 percent (there is a 1 percent hysteresis value added by the positioner). At this point, the
stem position will follow the command signal. While in Final Value Cutoff, the Logix 3400IQ LEDs will
blink GGGY.
Q: I have Final Value Cutoff set to 3 percent but the valve will not go below 10 percent.
A: Is a lower soft stop enabled? The lower soft stop must be less than or equal to zero percent in
order for the Final Value Cutoff to become active. If a positive lower soft stop is written, this stop will
take priority over the Final Value Cutoff feature. When the lower soft stop is reached, the positioner
will blink a GYYR code.
Q: Will soft stops prevent the valve from going to its fail position?
A: No.
Q: What is the difference between a model with Standard diagnostics and a model with Advanced
diagnostics?
A: The model with Advanced diagnostics adds top and bottom actuator pressure sensors. This
allows for more diagnostic calculations such as loss of pressure, friction, advanced signatures, and
troubleshooting. The pressure sensors, if present, are also used in the positioner control algorithm to
enhance valve stability.
Q: Can I upgrade from a Standard to an Advanced?
A: Yes. Referencing the IOM, an advanced pressure sensor board assembly can be purchased.
Simply replace the pressure sensor plug plate with the advanced pressure sensor board. Perform an
actuator pressure calibration.