Watlow Series F4S/D - Manual (Page 137)

form A
— A single-pole, single-throw relay that us-
es only the normally open (NO) and common con-
tacts. These contacts close when the relay coil is en-
ergized. 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.
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.
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.
process variable — The parameter that is con-
trolled or measured. Typical examples are tempera-
ture, relative humidity, pressure, flow, fluid level,
Wa t l o w S e r i e s F 4 S / D A p p e n d i x ■ A . 3