10
SOAK TIMER OPERATION
Figure 5.1
SP
PV
Time
PV
Set Time
Timer count down starts
PV enters start band,
Start Band
Basic Operation
The Soak Timer is essentially a Setpoint Dependent Timer. That is, after issuance of Start Command, the count down starts
only after the Temperature Value reaches within timer ‘Start Band’. The timer start band is a symmetrical band centered
around the Control Setpoint. For example, for a start band of 1.0°C and Control Setpoint value of 121.0°C, the count down
begins once the Temperature Value reaches within 120.0°C (Control Setpoint - Start Band) to122.0°C (Control Setpoint +
Start Band). Note that, once the Temperature Value enters ‘Start Band’, the timer continues to run regardless of whether the
Temperature Value remains within or outside the ‘Start Band’.
Hold Band Operation
The timer is also provided with a ‘Hold Band’ that can be enabled to make sure that the timer counts down only while the
Temperature Value is within the ‘Hold Band’. That is, the timer pauses (stops counting down) whenever the Temperature Value
is outside the ‘Hold Band’. The ‘Hold Band’ is set with respect to the Control Setpoint and can be set above or below or above
and below the Control Setpoint. For example, a 1.0°C Hold Band below the Control Setpoint (say,121.0°C) will force the timer
in pause state whenever the Temperature Value is equal to or less than 120.0°C (Control Setpoint - Hold Band).
Power-fail Recovery Modes
The timer facilitates 3 different power-fail recovery modes, viz., Continue, Re-start and Abort. In Continue mode, the timer
resumes to execute the balance soak time once the Temperature Value is detected within Hold Band. In Re-start mode, the
timer executes the complete set time all over again. In Abort mode, the timer stops execution until a start command is issued.
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