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input failure, or a heater or load failure.
Loop Break Time - the time interval from when the controller detects a
loop break condition and the initiation of the failsafe state.
Lowest Reading - records the lowest process value read by the controller.
May be reset to zero by using the Raise or Lower arrow keys.
Lower Setpoint Limit - prohibits users from adjusting the setpoint lower
than the selected value.
Manual Reset - an adjustment that moves the Proportional Band up or
down by a fixed percentage so that more or less power is applied at set-
point. It is used to eliminate offset error.
On/Off Output Type - In a heating application, the controller applies 100%
output power if the process temperature is below the setpoint and 0% at
the setpoint. For a cooling application, the controller applies 100% output
power if the process temperature is above the setpoint and 0% output
power at the setpoint. There are only two output states: fully on and fully
off.
Applications for On/Off Control:
1. When temperature oscillation is acceptable.
2. When constant cycling of mechanical devices is
prohibited (Compressors, Blowers, etc.)
3. Under-powered processes
Output Low Limit % - Prohibits the controller’s output from going
below the specified percentage.
Output High Limit % - Prohibits the controller’s output from going above
the specified percentage.
PID Output Type (Proportional - Integral - Derivative) - 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. PID control helps
reduce overshoot on start-up, enhances stability, and compensates for
process lag. The PID parameters are automatically calculated for a par-
ticular application during the autotune procedure.
Applications for PID Control:
1. Where process temperature lags exist
2. When load changes are present
3. When overshoot is prohibited
4. When very accurate control is required
Proportional Band - the band (expressed in degrees of temperature) in
which the controller modulates its power percentage.
Temperature Lag - The product of thermal resistance and thermal capac-
ity. Also defined as delay of the transmission of heat from the controlled
element to the sensor caused by thermal mass of the process material
and/or process container, or the distance between the control element
and the sensor.
Upper Setpoint Limit - prohibits users from adjusting the setpoint higher
than the selected value.
Glossary