SP
PV
Time Reset by
User
5-2-1-2 Operation of Limit Functions when O.ACT = FWD, HI.LO = HIGH, R.MD = OFF
Fig 4: Operation of Limit Functions with O.ACT set to FWD
HYS
The following illustration shows how each aspect of the limit control functions behave under over limit circumstances when
O.ACT is set to FWD operation.
1. Power supplied to the controller. The limit control relay energizes.
2. The PV surpasses the SP. The OUT LED turns off. the OVER LED turns on. The latching limit control relay energizes.
The time begins being recorded.
3. The PV falls below the limit and hysteresis levels. The OVER LED turns off. The time count stops.
4. The PV surpasses the SP. The OVER LED turns on. The time count resets and begins again.
5. The PV falls below the limit and hysteresis levels. the OVER LED turns off. The time count stops.
When the rest button is pressed for 3 seconds, and the PV is below the SP, the OUT LED will turn on, and the limit control
relay will turn off.
OUT
LED
Limit
Control
Relay
OVER
LED
Time
Count
Power
to Unit
Reset
Pressed
ON
OFF
ON
OFF
ON
OFF
ON
OFF
2 3 4 5
Reset
Pressed
Reset
Pressed
(not accepted)
1
PD570 Series Nova Process and Temperature Limit Controller Instruction Manual
20
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