Watlow Series F4P - Manual (Page 114)

A . 6 ■ A p p e n d i x Wa t l o w S e r i e s F 4 P
tacts. 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 us-
es only the normally closed (NC) and common con-
tacts. These contacts open when the relay coil is en-
ergized. 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.
Hertz (Hz) — Frequency, measured in cycles per
second.
hysteresis — A change in the process variable re-
quired to re-energize the control or alarm output.
Sometimes called switching differential.
integral — Control action that automatically elim-
inates offset, or droop, between set point and actual
process temperature.
integral control (I) — A form of temperature con-
trol. The I of PID. See integral.
inverse scaling — The relationship between the
low and high scale value and the process input or
output. Minimum process signal is represented by
scale high value and maximum process signal is
represented by scale low value.
isolation — Electrical separation of sensor from
high voltage circuitry. Allows use of grounded or
ungrounded sensing element.
JIS — See Joint Industrial Standards.
Joint Industrial Standards (JIS) — 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 In-
dustrial Norm (DIN).
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).
LCD — See liquid crystal display.
LED — See light emitting diode.
light emitting diode (LED) — A solid state elec-
tronic device that glows when electric current pass-
es through it.
liquid crystal display (LCD) — A type of digital
display made of a material that changes reflectance
or transmittance when an electrical field is applied
to it.
limit or limit controller — A highly reliable, dis-
crete safety device (redundant to the primary con-
troller) that monitors and limits the temperature of
the process, or a point in the process. When tem-
perature exceeds or falls below the limit set point,
the limit controller interrupts power through the
load circuit. A limit controller can protect equip-
ment and people when it is correctly installed with
its own power supply, power lines, switch and sen-
sor.
manual mode — A selectable mode that has no
automatic control aspects. The operator sets output
levels.
Modbus ™ — A digital communications protocol
owned by AEG Schneider Automation for industrial
computer networks.
Modbus ™ RTU — Remote Terminal Unit, an indi-
vidual Modbus ™ -capable device on a network.
NEMA 4X — A NEMA (National Electrical Manu-
facturer’s Association) specification for determining
resistance to moisture infiltration. This rating cer-
tifies the controller as washable and corrosion re-
sistant.
normal scaling — The relationship between the
low and high scale value and the process input or
output. Minimum process signal is represented by
scale low value and maximum process signal is rep-
resented by scale high value.
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.
page — A fixed length block of data that can be
stored as a complete unit in the computer memory.
P control — Proportioning control.
PD control — Proportioning control with deriva-
tive (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 un-
dershoot.