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Whether operating as a linear or non-linear device, the positioner has two distinct modes of operation, Normal Mode and Setup Mode.
In Normal Mode the positioner simply positions its actuator in response to the 4-20mA input signal. When the positioner is powered up, it always starts in Normal Mode. In Normal Mode, the LEDS are not lit. The positioner stays in Normal Mode until Setup Mode is selected manually.
In Setup Mode the positioner can be tuned and calibrated for its application. Although the position is still controlled, it does not always follow the input signal. When tuning and calibration is complete the positioner should always be returned to Normal Mode
for continued normal use.
Operating in Setup Mode is described in the following sections.
4.4 Default Settings and Reset Procedure.
The positioner can be reset with a complete set of default values when powered up in any operating mode, by pressing all three push buttons (UP, DOWN and SET) simultaneously. This will overwrite all the existing proportional gain, damping, curve
selection and calibration data with default values which are suitable for a typical forward acting linear positioner with mid range values for proportional gain and damping (but not necessarily optimised for a particular application). This procedure is useful in the case where errors in calibration have resulted in positioner behaviour which seems incomprehensible, and it is necessary to return to a predictable basic setup. The positioner should always be tuned and then recalibrated immediately after this resetting process.
4.5 Entering and Leaving Setup Mode.
Setup Mode is selected from Normal Mode by simultaneously pressing the UP and the SET push buttons (i.e. the two outside ones). This causes the LED labelled PGAIN (short for Proportional Gain) to light continuously. In Setup Mode, each of the parameters in the list below may be selected for adjustment by pressing the UP or DOWN push buttons as required. The parameter selected is indicated on the positioner circuit by an LED lighting next to the parameter's name.
PGAIN - Proportional Gain
DAMP - Damping
CURVE - Non-Linear Curve Selection
LOW - Low Current Point Calibration
HIGH - High Current Point Calibration
POT - Feedback Potentiometer Bottom of Range Setting
When the required parameter has been selected for adjustment, the SET push button is pressed to allow adjustments to be made – the LED next to the selected parameter starts to blink, to indicate that Adjust Mode is active. Operation in the Adjust Mode for each parameter is described in the following sub-sections. To leave Adjust Mode, press the SET push button again – this causes the LED to light continuously, and allows movement between parameters again.
Note: There is no Adjust Mode for the feedback potentiometer bottom of range setting, but the automatic end stop finding sequence can be initiated when this parameter is selected.
To leave set up mode (when the adjustments have been made and the SET push button pressed to leave Adjust Mode), press the DOWN push button repeatedly to move down the parameter's and off the end of the list – at this point the LEDs cease to light, and the positioner is back in Normal Mode.
4.6 Automatic Endstop Finding Procedure.
The positioner can automatically calibrate itself to range between any mechanical end stops (either the built-in actuator stops, or any external stops built into the application). During the finding sequence, the positioner moves the actuator up to the top and bottom stops and records their positions. It then uses these positions as the HIGH and LOW positions in the calibration data, and applies the existing values for HIGH and LOW current input. Note that if the positioner was reverse acting before the sequence, it remains so after the sequence.