ControlMaster CM30, CM50 and CMF310
Universal process controllers,
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4
,
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2
DIN and fieldmount
7 Advanced Level
64
IM/CM/ED–EN Rev. X
7.6.4 Retort Function
The Retort function ensures safe operation of retort vessels under fault conditions. If the heat source fails
during a soak segment, the process variable will inevitably fall. When the process variable falls below the
holdback hysteresis value the program is put on HOLD (as for normal operation). The set point then follows
the process variable as it continues to fall (Retort Hold).
Set Point = Process Va Hysteresis value
Upon recovery of the heat source, the process is controlled at the new set point value. When the process
variable reaches the set point it is then ramped back to the initial soak value at the rate of the previous ramp
(Retort Ramp). When the soak level is reached the program is released from its hold state and the segment
is either completed or repeated from the beginning, depending on the retort mode selected.
The retort mode is selected in the
Ramp / Soak Profile
page.
Note.
For the retort function to operate, either LO or HI-LO hysteresis must be applied to the soak
segments.
1
The program is put on HOLD when the process variable falls below the holdback hysteresis.
2
The setpoint follows the process variable as it continues to fall. (SP = PV + hysteresis).
The set point 'tracks the lowest value of the process variable.
3
When the process variable reaches the set point, the set point is ramped back to the
soak level at the rate of the previous ramp.
4
Upon reaching the soak level, 'HOLD' is released and the segment is completed or repeated.
Fig. 7.4 Retort Function
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2
3
4
Program on hold
Seg. 1
Seg. 2
Recovery of heat source
Failure of heat source
Set point
Process variable
Hysteresis applied to
soak segment