West Control Solutions 8700+ - Manual (Page 162)

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- DIN Controllers & Indicators - Product Manual
59305, Issue 7
– March 2014 Glossary Page 157
Tare Type: Indicator Parameter
When an Indicator’s Tare function has been enabled, the operator can set the current
Process Variable input value to be displayed as zero. This function may be used to easily
eliminate any offset on the input signal, e.g. when a transducer output is not giving a true
zero value. It may also be used in applications displaying the weight of a product, to remove
the weight of a container before starting. When Tare is activated, the instrument
automatically sets the PV Offset to an equal, but opposite value to the current measured
value.
Display code =

, default setting =

(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.