Specifications

WESTLOCK CONTROLS CORPORATION
280 MIDLAND AVENUE, SADDLE BROOK, NJ 07663 TEL: [phone] FAX: [phone]
www.westlockcontrols.com
1/12/10 TECH-439/D.W.O. 19024 Page 30 of 58
HI This function serves to set the fully energized (full travel) position of the
actuator/valve. initially during this calibration the valve is driven to the fully
energized (full travel) position (hard stop). The user will notice full pressure to
Outlet Port 1 and zero pressure to Outlet Port 2. At this point the user has the
option to select the hard stop as the high (span) position. or to select an
arbitrary position as the high (span) position.
PID The PID function allows the user to modify the PID settings of the positioner so
the user can optimize the dynamic response of the positioner regarding the
speed of response, overshoot and steady-state error by varying the
appropriate gain settings. This function is often used to fine tune the PID values
obtained from the automatic calibration function (ACAL). The PID entry allows
the user to modify the tuning parameters in three different ways:
1. Auto PID: this option triggers the Auto PID procedure. It will override the
positioner control and will modulate the valve in order to automatically find out
the best P, I and D parameters.
2. Manual PID: the Manual Proportional (PCAL) and Derivative (DCAL)
gain settings can be varied incrementally on a scale from 1-20. The Integral
(ICAL) gain setting can be varied incrementally on a scale from 1-5. The
Manual PID values are actually index representations of the Fine Tune settings
that are reported through the HART communication.
3. Fine Tuning: the Fine Tune Proportional (PCAL), Derivative (DCAL)
and Integral (ICAL) gain settings can be varied incrementally on a scale from
1-255. The fine tuning values are directly related to the actual time constant
values (Ti or Td) and the Proportional gain value (Kc). The proportional gain
(Kc) has a direct effect in the system response time. So, as higher the Kc as
faster is the response time. The drawback of increasing the value of the Kc is
the higher overshoot and settling time. Sometimes the valve’s position control
becomes instable, oscillating for ever around the set point. The integrative term
(Ti) affect the dynamic response of the position control by damping the
positioner response according to the Ti value. So as lower the value of Ti as
less damped is the dynamic response. This means that as lower the Ti as more
oscillations are observed before the stabilization of the position and vice-versa.
However, as higher the Ti as higher will be the settling time. Regarding the
Derivative term (Td), as greater is its value as greater will be the derivative
effect. Different from the proportional gain and integrative term, the derivative
term is not proportional to the error but the variation of the position. The effect
of Td is to decrease the overshoot and the control reacts against the variation
of the position. The drawback is that as higher the Td as unstable can be the
control system.
Snsr The sensor calibration is a self adjustment that sets the positioner’s Hall-Effect
circuitry. This is automatically done during the ACAL (Automatic Calibration)