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…3
PROFILES
3.2.2
Guaranteed Ramp/Soak
If the process variable deviates from the set point by more than the hysteresis value, the program status is set to
'
HOLd
' and Guaranteed ramp/soak is applied automatically. Each program has two associated hysteresis values:
HYS.r
–
applied to ramping segments, and
HYS.S
–
applied to soak segments.
The hysteresis value can be set within the limits '0' to '9999' where a setting of '0' implies that no deviation from the
set point value can be tolerated.
Hysteresis can be applied in one of four ways, with individual settings for each segment:
OFF
–
hysteresis not applied, ramp/soak not guaranteed.
HI
–
hysteresis applied above set point ( Holdback ('
HOLd
') set if PV > [SP + Hysteresis]).
LO
–
hysteresis applied below set point ( '
HOLd
' set if PV < [SP – Hysteresis]).
HI.LO
–
hysteresis applied above and below set point
( '
HOLd
' set if PV > [SP + Hysteresis] or PV < [SP – Hysteresis]).
Set
Point
Time (Hours or Minutes)
Process
Seg. 1
Seg. 2
Seg. 4
Seg. 5
End of Profile (revert
to Local Set Point or
repeat of profile)
Set P
oint (Eng.
Units)
Adjustable Holdback Hysteresis
1. for Ramp segments
2. for Soak segments
Adjustable ramp rates
Skip Forward
Manual
Pause
Holdback Active
outside hysteresis
limits
Hysteresis applied Hi-Lo
(above and below the set point)
Hysteresis applied Hi
(above the set point)
Start
Seg. 3
Note. Ramp segments can have a different hysteresis to soak segments.
Fig 3.4 Typical 6-segment Ramp/Soak Profile
3.2.3
Power Recovery Function
The Power Recovery function allows pre-selection of the restart position within a ramp/soak profile when power is
restored after a failure.
With options
A
,
b
or
C
, if power is restored before the
Power Down Time
expires, the ramp/soak profile continues
from the point at which power failed. If power is restored after the
Power Down Time
has expired, the profile resumes
from one of the following user-selected points: start of the current program; start of the current segment or from the
profile position at the time of failure. In all three cases the controller restarts in
HOLD
mode.
With option
d
, the profile continues in run mode from the position on the profile that would have been reached had
the power failure not occurred.