Despatch P1400+ Temperature Controller - Manual (Page 97)

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Display code = tArE , default setting = diSA (disabled).
Also refer to Indicator , Process Variable , and Offset .
Three Point Stepping Control Type: VMD Controller Definition
Refer to Valve Motor Control .
Time Proportioning Control Type: Controller Definition
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. This type of output might be
used with electrical contactors, Solid State Relays 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 Type: Controller Definition
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 Type: General Definition
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 .
Valve Close Limit Type: VMD Controller Parameter
When Valve Position Indication is to be used on Valve Motor Controllers, this parameter
provides a “clamp” on the upper valve position, which the controller will not attempt to drive the valve
past. It can be set between
0000
(fully closed) and the Valve Open Limit value –1, expressed as a
percentage of the valve’s “fully open” position.
The Auxiliary Input must correctly scaled using the Set Valve Open and Closed parameters before
using this parameter.
Display code =
PiUL , default setting = 0 .
Also refer to Auxiliary Input , Set Valve Closed Position , Set Valve Open Position , Valve Open
Limit , Valve Motor Control and Valve Position Indication .