Installation manual

Series C Controller Configuration and Operation Manual
1-8  Athena Controls, Inc. 900M050U00
1.5 Control Types Supported
1.5.1 Overview
The 1ZC, 16C, 18C, and 25C controllers support PID and on/off control. Autotuning is
available for PID control. The type of control for each of the two standard outputs
3
is
specified using the output menu output type parameter. The two outputs can be set for
different types of control. For 1ZC and 16C controllers, one or both standard outputs can
be used for alarm annunciation instead of control. (See 1.6 for more information about
alarm annunciation.)
The advantages and disadvantages of both types of control are described briefly below.
1.5.2 PID Control
When Proportional-Integral-Derivative (PID) control is used, the controller modulates
output power by adjusting the output power percentage within a proportional band.
Power is proportionally reduced as the process temperature gets closer to the setpoint
temperature. The integral action affects the output based on the duration of the process
value’s variation from the setpoint, and the derivative action affects the output based on
the rate of change of the process value.
PID control has the following advantages:
• minimizes overshoot
• enhances stability
• compensates for process lag
The proportional band, derivative action (rate), and integral action (auto reset)
parameters are automatically adjusted by the Autotune operation described in Section
16.
PID control is appropriate for processes with the following characteristics:
• temperature lags exist
• load changes are present
• overshoots need to be minimized
• very accurate control is required
PID is not appropriate for:
• underpowered processes
• processes that use compressors, blowers, or other mechanical devices that
cannot tolerate constant cycling
3
If your application does not require two outputs, the controller could have been ordered with only one
output (output 1).