Xylem PC320 Process Controller - Manual (Page 10)

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Relay Modes:
Off: In Off mode, relays will not turn on regardless of settings
One Time: In One Time mode, a relay will turn on one time only when a sensor
reading is above or below a threshold level. The relay will turn on for the programmed
On Time, then turn off regardless of sensor reading. If during the On Time the sensor
reading returns to a normal range, the relay will turn off even if the On Time has not
elapsed. Once the On Time has elapsed, the relay will remain off until the sensor
reading returns to a normal level (between thresholds), and then crosses past a
threshold level again. The Off Time does not apply in this mode and has no effect on
relay operation, the Delay Time and Hysteresis settings do apply.
Steady: In Steady (Steady State) mode the relay will turn on when a sensor reading is
outside of the normal range, and stay on. The relay will remain on as long until the
sensor reading is outside of the threshold points. The Delay Time and Hysteresis
settings are used in this mode. Programmed ON and Off times do not apply.
Cyclic: In cyclic mode the relay will trigger when a sensor reading falls outside of the
threshold settings. The relay will turn on for the On Time, then off for the Off Time.
The cycle of on and off will continue until the sensor reading falls within a normal
range again. The Delay Time and Hysteresis setting apply in this mode.
High Control: In High Control mode, the relay will turn on when the sensor reading
rises above the Upper Threshold. The relay will remain on until the sensor reading
falls below the Lower Threshold. This mode could be used to turn on a pump when a
water level rises above 10 feet and continue to pump until the level falls below 5 feet.
Delay Time does apply. On Time, Off Time and Hysteresis do not apply and have no
effect on relay operation.
Low Control: This mode is the opposite of High Control mode. The relay will turn
on when a sensor reading falls below the Lower Threshold and remain on until the
sensor reading rises above the Upper Threshold. This might be used to pump water
into a tank when the level falls below 5 feet and continue to pump until the level rises
above 10 feet. Delay Time does apply. On Time, Off Time and Hysteresis do not
apply and have no effect on relay operation.