User`s manual

Glossary
A-20 Appendix 6 535 User's Manual
modules are either binary (on/off)
such as a relay, or analog
(continuously variable) for current
loop control.
output: Action in response to
difference between setpoint and
process variable.
overshoot: Condition where
temperature exceeds setpoint due to
initial power up or process changes.
P control: Proportioning control.
parameter(s): A user-defined
variable that specifies how a
particular function in the 535 will
operate.
PD control: Proportioning control
with rate action.
PI control: Proportioning control
with auto-reset.
PID control: Proportioning control
with auto-reset and rate.
position proportioning: A type of
control output that utilizes two relays
to control an electric motorized
actuator.
POWERBACK®: Powers
proprietary algorithm which monitors
the PV to make predictive
judgements to control parameters in
order to reduce or eliminate
overshoot at powerup or after
setpoint changes.
POWERTUNE®: The Powers
exclusive special self-tuning
function. Consists of an on-demand
pretune that calculates PID values
or provide preliminary PID values
and process information for the
second tuning function. Second
tuning function is an adaptive tuning
algorithm that automatically adjusts
PID values whenever a process
upset or setpoint change occurs.
pretune algorithm: A method by
which the 535 controller initiates an
output value change, monitors the
manner of the corresponding
process variable change, and then
determines the appropriate PID
control parameters.
primary loop: The outer loop in a
cascade system.
process variable: In the treatment
of material, any characteristic or
measurable attribute whose value
changes with changes in prevailing
conditions. Common variables are
level, pressure and temperature.
proportional band: The change in
input required to produce a full
range change in output due to
proportional control action.
ramping: (see setpoint, ramping)
rate: Anticipatory action that senses
the rate of change of temperature
and compensates to minimize
overshoot. Also “derivative.”
rate action: The derivative function
of a controller.
rate time: The time interval over
which the system temperature is
sampled for the derivative function.
regulate: The act of maintaining a
controlled variable at or near its
setpoint in the face of load
disturbances.
relay (mechanical): An
electromechanical device that
completes or interrupts a circuit by
physically moving electrical contacts
into contact with each other.
relay (solid state): A solid state
switching device which completes or
interrupts a circuit electrically with no
moving parts.
reset: Control action that
automatically eliminates offset, or
“droop,” between setpoint and actual
process temperature. Also “integral.”
reset term: (see reset)
RTD: Resistance Temperature
Detector. Resistive sensing device
displaying resistance versus
temperature characteristics.
Displays positive temperature
coefficient.
relative gain: An open-loop gain
determined with all other
manipulated variables constant,
divided by the same gain
determined with all other controlled
variables constant.
retransmission: a feature on the
535 which allows the transmission of
a milliamp signal corresponding to
the process variable, target setpoint
or actual setpoint to another device,
typically a chart recorder.
sample interval: The time interval
between measurements or
observations of a variable.
secondary loop: The inner loop of
a cascade system.
self tune: A method of automatically
calculating and inserting optimum
PID parameters by testing system
response and timing.
serial communications: The
sending or receiving of binary coded
data to a supervisory device such as
a personal computer of
programmable logic controller.
setpoint: An input variable which
sets the desired value of a controlled
variable.
setpoint, actual: The desired value
of a controlled variable that the
controller is currently acting upon.