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GLOSSARY (continued):
CURRENT STEP LIMIT The current step limit is a maximum value that the analog
output will be allowed to change from one control cycle to
another. The current step limit is used to prevent rapid or erratic
control action of the actuator even under transient conditions or
with a poorly tuned control system. A limit of about 2 ma or
about 10 % of the output range is reasonable default value.
CYCLE TIME The time taken between adjustments of the PRIMARY
CONTROL loop. The longer the cycle time selected the less
responsive the control output is to variations in the controlled
parameter. The cycle time is adjustable from 1 to 999 seconds.
DEADBAND The controller deadband defines a user programmed value
both above and below the setpoint for which no corrective
action will be taken. Deadband is used to improve control
stability by holding the controller output constant in the
presence of “noise” or small transient errors on the input.
DIRECT ACTING When describing control or actuator functions, direct acting is
used to identify relationships where the controller must increase
its output to cause an increase in the variable.
INVERSE ACTING When describing control or actuator functions, inverse acting is
used to identify relationships where the controller must
decrease its output to cause an increase in the variable.
MAXIMUM RPM The maximum RPM setting is the highest governor setpoint
value which will be sent by the controller in an attempt to satisfy
the primary control setpoint. The maximum running RPM.
MINIMUM RPM The minimum RPM is the governor setpoint value which will be
sent by the controller after the warmup delay time has been
fulfilled. The minimum RPM is the speed which must be seen by
the controller to allow loading of the compressor to begin.
OVERCRANK TIME The maximum time that the starting device will remain
energized by output # 3 before the starting attempt is
considered failed. If an overcrank occurs, the crank disconnect
RPM is not reached before the overcrank time, then an
overcrank fault has occurred.
PRE-LUBE TIME A user programmed time for which output # 4 will remain ON
after the beginning of an AUTO START sequence. Normally
used for control of a pre-lube pump and to signal that a starting
attempt is about to begin.
PRIMARY CONTROL The primary control is a closed loop based upon an input value
selected from channels 30, 31, or 32. The throughput of the
compressor is adjusted by the controller to maintain this
setpoint.
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