Programmer Operation Installation and Operation Handbook
5.5.3
Power failure
If power is lost and then restored, while a program is running, the behaviour of the programmer is determined by
the setting of the parameter ‘
Pwr.F
’
Power fail strategy
in Programmer configuration. This can have one of three
settings:
−
cont
(Continue),
rmP.b
(Ramp from PV), or
rSEt
(Reset).
If ‘
cont
’ is selected,
then when power is restored the program continues from where it was interrupted when
power was lost. All parameters, such as the setpoint and time remaining in the active segment, will be restored to
their power-down values. For applications that need to bring the measured process value to the setpoint as soon
as possible, this is the best strategy.
If ‘
rmP.b
’ is selected,
then when power is restored the setpoint starts at (‘servos to’) the current measured value,
and then ramps to the target setpoint of the active segment at the last ramp rate used by the program. This
strategy provides a smoother recovery. The two diagrams below illustrate the respective responses, Figure 5-2 if
power fails during a dwell segment and Figure 5-3 if it fails during a ramp segment.
Figure 5-2: Continue after a power fial
Figure 5-3: Ramp back after a power fail
If ‘
rSEt
’ is selected,
then when power is restored the program terminates.
Setpoint
Ramp
Segment
Dwell Segment
Time
t1
t2
Segment dwell time = t1 + t2
Power off
Power on
Setpoint
Ramp Segment
Time
Power off
Power on -
Servo to new PV level
Target setpoint
5-6 HA025041 issue 12 Aug 14
Summary of Contents for XST-2-0-12-1V1-E28
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