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Time Proportioning Control
Time proportioning control is accomplished by cycling the output on and off, during the
prescribed cycle time, whenever the process variable is within the proportional band. The
control algorithm determines the ratio of time (on vs. off) to achieve the level of output power
required to correct any error between the process value and setpoint. E.g. for a 32 second
cycle time, 25% power would result in the output turning on for 8 seconds, then off to 24
seconds. Time proportioning control can be implemented with Relay, Triac or SSR Driver
outputs for either primary (Heat) or secondary (Cool) outputs depending on hardware
configuration.
Also refer to Current Proportioning Control, Cycle Time, PID, Primary Proportional Band,
Process Variable, Secondary Proportional Band, Setpoint, SSR and Triac.
Tuning
PID Controllers must be tuned to the process in order for them to attain the optimum level of
control. Adjustment is made to the tuning terms either manually, or by utilising the controller's
automatic tuning facilities. Tuning is not required if the controller is configured for On-Off
Control.
Also refer to Automatic Reset, Auto Pre-Tune, On-Off control, PID, Pre-Tune, Primary
Proportional Band, Rate, Self-Tune and Secondary Proportional Band.
Triac
A small internal solid state device, which can be used in place of a mechanical relay in
applications switching low power AC, up to 1 amp. Like a relay, the output is time
proportioned, but much faster switching cycle times are also possible, leading to superior
control. As a solid-state device, a Triac does not suffer from contact degradation when
switching electrical currents. A triac cannot be used to switch DC power.
Also refer to Cycle Time, SSR and Time Proportioning Control.
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Glossary
- DIN Controllers & Indicators - Product Manual
59305, Issue 5 – March 2005
Type: Controller Definition
Type: Controller Definition
Type: General Definition
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