Watlow Series 988LF - Manual (Page 56)

A.2 WATLOW Series 988LF Users Manual Appendix
Glossary
annunciator — A visual display that uses pilot lights to
indicate the former or existing condition of several items in a
system.
bumpless transfer — A smooth transition from auto (closed
loop) to manual (open loop) operation. The control output(s)
does not change during the transfer.
burst fire — A power control method that repeatedly turns on
and off full AC cycles. Also called zero-cross fire, it switches
close to the zero-voltage point of the AC sine wave. Variable-
time-base burst fire selectively holds or transits AC cycles to
achieve the desired power level.
calibration offset — An adjustment to eliminate the differ-
ence between the indicated value and the actual process
value.
cascade — Control algorithm in which the output of one
control loop provides the set point for another loop. The
second loop, in turn, determines the control action.
closed loop — A control system that uses a sensor to measure
a process variable and makes decisions based on that
feedback.
cold junction — See junction, cold.
cold junction compensation — Electronic means to compen-
sate for the effective temperature at the cold junction.
current transformer — A transformer designed for measuring
electrical current.
dead band — The range through which a variation of the
input produces no noticeable change in the output. In the
dead band, specific conditions can be placed on control output
actions. Operators select the dead band. It is usually above
the heating proportional band and below the cooling propor-
tional band.
default parameters — The programmed instructions that are
permanently stored in the microprocessor software.
derivative — The rate of change in a process variable. Also
known as rate. See PID.
DIN (Deutsche Industrial Norm) — A set of technical,
scientific and dimensional standards developed in Germany.
Many DIN standards have worldwide recognition.
DIN-a-mite — Watlow family of SCR power controls.
droop — In proportional controllers, the difference between
set point and actual value after the system stabilizes.
duty cycle — The percentage of a cycle time in which the
output is on.
external signal conditioner power supply — A dc voltage
source that powers external devices.
filter —
digital filter (DF) — A filter that slows the response
of a system when inputs change unrealistically or too fast.
Equivalent to a standard resistor-capacitor (RC) filter.
digital adaptive filter — A filter that rejects high
frequency input signal noise (noise spikes).
heat/cool output filter — A filter that slows the
change in the response of the heat or cool output. The output
responds to a step change by going to approximately 2/3 its
final value within the number of scans that are set.
form A — A single-pole, single-throw relay that uses only the
normally open (NO) and common contacts. These contacts
close when the relay coil is energized. They open when power
is removed from the coil.
form B — A single-pole, single-throw relay that uses only the
normally closed (NC) and common contacts. These contacts
open when the relay coil is energized. They close when power
is removed from the coil.
form C — A single-pole, double-throw relay that uses the
normally open (NO), normally closed (NC) and common
contacts. The operator can choose to wire for a Form A or
Form B contact.
hunting — Oscillation of process temperature between the set
point and the process variable.
hysteresis — A change in the process variable required to re-
energize the control or alarm output. Sometimes called
switching differential.
integral — Control action that automatically eliminates offset,
or droop, between set point and actual process temperature.
See reset, automatic.
isolation — Electrical separation of sensor from high voltage
circuitry. Allows use of grounded or ungrounded sensing
element.
JIS (Joint Industrial Standards) — A Japanese agency that
establishes and maintains standards for equipment and
components. Also known as JISC (Japanese Industrial
Standards Committee), its function is similar to Germany’s
Deutsche Industrial Norm (DIN).
junction — The point where two dissimilar metal conductors
join to form a thermocouple.
cold junction — Connection point between thermo-
couple metals and the electronic instrument. See reference
junction.
grounded junction — Type of thermocouple probe in
which the hot, or measuring junction, is an integral part of the
sheath material. No electrical isolation is provided.
isolated junction — A form of thermocouple probe
construction in which the measuring junction is fully enclosed
in a protective sheath and electrically isolated from it.
Commonly called an ungrounded junction.
reference junction — The junction in a thermo-
couple circuit held at a stable, known temperature (cold
junction). Standard reference temperature is 32°F (0°C).
thermocouple junction — The point where the two
dissimilar metal conductors join. In a typical thermocouple
circuit, there is a measuring junction and a reference junc-
tion. See reference junction.
ungrounded junction — See isolated junction.
linearization, square root — The extraction of a linear signal
from a nonlinear signal corresponding to the measured flow
from a flow transmitter. Also called square root extraction.