Watlow Series 982 - Manual (Page 133)

Appendix WATLOW Series 982 User’s Manual A.3
Glossary, N-R
junction, cold — Connection point between ther-
mocouple metals and the electronic instrument. See
junction, reference.
junction, reference — The junction in a thermo-
couple circuit held at a stable, known temperature
(cold junction). Standard reference temperature is
32°F (0°C).
NEMA 4X — A NEMA specification for determining
resistance to moisture infiltration. This rating certi-
fies the controller as washable and corrosion resis-
tant.
on/off controller — A temperature controller that
operates in either full on or full off modes.
open loop — A control system with no sensory
feedback.
output — Control signal action in response to the
difference between set point and process variable.
overshoot — The amount by which a process vari-
able exceeds the set point before it stabilizes.
P control — Proportioning control.
PD control — Proportioning control with derivative
(rate) action.
PDR control — Proportional derivative control with
manual reset, used in fast responding systems
where the reset causes instabilities. With PDR con-
trol, an operator can enter a manual reset value that
eliminates droop in the system.
PI control — Proportioning control with integral
(auto-reset) action.
PID — Proportional, integral, derivative. A control
mode with three functions: proportional action
dampens the system response, integral corrects for
droop, and derivative prevents overshoot and
undershoot.
proportional — Output effort proportional to the
error from set point. For example, if the proportional
band is 20° and the process is 10° below set point,
the heat proportioned effort is 50 percent. The lower
the PB value, the higher the gain.
proportional band (PB) — A range in which the
proportioning function of the control is active.
Expressed in units, degrees or percent of span. See
PID.
proportional control — A control using only the P
(proportional) value of PID control.
range — The area between two limits in which a
quantity or value is measured. It is usually
described in terms of lower and upper limits.
rate — Anticipatory action that is based on the rate
of temperature change, and compensates to mini-
mize overshoot and undershoot. See derivative.
rate band — A range in which the rate function of a
controller is active. Expressed in multiples of the
proportional band. See PID.
reference junction — see junction, reference.
remote — A controller that receives its set point
signal from another device called the master.
remote set point — A signal that indicates the set
point for the process, and is sent from another
device.
reset — Control action that automatically eliminates
offset, or droop, between set point and actual
process temperature. Also see integral.
automatic reset — The integral function of
a PI or PID temperature controller that adjusts the
process temperature to the set point after the sys-
tem stabilizes. The inverse of integral.
automatic power reset — A feature in
latching limit controls that does not recognize power
outage as a limit condition. When power is restored,
the output is re-energized automatically, as long as
the temperature is within limits.
manual reset — 1) A feature on a limit
control that requires human intervention to return
the limit to normal operation after a limit condition
has occurred. 2) The adjustment of a proportional
control to raise the proportional band to compensate
for droop.