Rev 007, 04/12 21
© SP Scientific 2012
Proportional Control Menu
Ramp Rate. Programmed transition rate from old setpoint to new setpoint, in degrees per
minute. Ramp Rate is more of a slew limiter, because the available ramp rate is obviously
limited by the thermal load and the pull-down capacities of the refrigeration system.
Cooling Band. Width of the temperature span across which cooling is proportionately
applied to the process, in degrees.
Note: this is band centered on the setpoint, so a CPb of 5 degrees defines a window that’s
+/- 2.5 degrees from the setpoint.
Integral (Automatic Reset) Time, in seconds. Is the time constant for adjustment of
proportioning action that serves to correct deviations from setpoint.
Derivative (Rate of Change adjustment) Time, in seconds. Time constant for
adjustment of proportioning action in order to reduce the slew rate of the process as it
approaches the setpoint. Derivative time is automatically limited to 1/4 of the Integral
Cool Cycle Time. Period of operation of the cool/bypass refrigeration valves, in seconds.
In order to reduce wear on the solenoids and valves, the period (total time on and off) may
never be less than two seconds. Additionally, the duration of either On or Off is never less
than 0.25 seconds.
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