Watlow Series F4S/D - Manual (Page 138)

events, etc. The high process variable is the highest
value of the process range, expressed in engineer-
ing units. The low process variable is the lowest
value of the process range.
proportional
— Output effort proportional to the
error from set point. For example, if the proportion-
al 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. Ex-
pressed in units, degrees or percent of span. See
PID.
proportional control
— A control using only the
P (proportional) value of PID control.
radio frequency interference (RFI) —
Electro-
magnetic waves between the frequencies of 10 KHz
and 300 GHz that can affect susceptible systems by
conduction through sensor or power input lines,
and by radiation through space.
ramp —
A programmed increase in the tempera-
ture of a set point system.
range
— The area between two limits in which a
quantity or value is measured. It is usually de-
scribed in terms of lower and upper limits.
rate — Anticipatory action that is based on the
rate of temperature change, and compensates to
minimize 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.
reset
— Control action that automatically elimi-
nates 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 pro-
cess temperature to the set point after the system
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 nor-
mal operation after a limit condition has occurred. 2)
The adjustment of a proportional control to raise the
proportional band to compensate for droop.
resistance temperature detector (RTD) — A
sensor that uses the resistance temperature charac-
teristic to measure temperature. There are two ba-
sic types of RTDs: the wire RTD, which is usually
made of platinum, and the thermistor, which is
made of a semiconductor material. The wire RTD is
a positive temperature coefficient sensor only, while
the thermistor can have either a negative or posi-
tive temperature coefficient.
RFI
— See radio frequency interference.
RTD
— See resistance temperature detector.
serial communications — A method of transmit-
ting information between devices by sending all
bits serially over a single communication channel.
set point
— The desired value programmed into a
controller. For example, the temperature at which a
system is to be maintained.
SI (Systeme Internationale) — The system of
standard metric units.
switching differential — See hysteresis.
thermal system
— A regulated environment that
consists of a heat source, heat transfer medium or
load, sensing device and a control instrument.
thermocouple (t/c) — A temperature sensing de-
vice made by joining two dissimilar metals. This
junction produces an electrical voltage in propor-
tion to the difference in temperature between the
hot junction (sensing junction) and the lead wire
connection to the instrument (cold junction).
thermocouple break protection
— The ability of
a control to detect a break in the thermocouple cir-
cuit and take a predetermined action.
time proportioning control — A method of con-
trolling power by varying the on/off duty cycle of an
output. This variance is proportional to the differ-
ence between the set point and the actual process
temperature.
transmitter — A device that transmits tempera-
ture data from either a thermocouple or a resis-
tance temperature detector (RTD) by way of a two-
wire loop. The loop has an external power supply.
The transmitter acts as a variable resistor with re-
spect to its input signal. Transmitters are desirable
when long lead or extension wires produce unac-
ceptable signal degradation.
WatView
— A Windows-based software application
for communicating with and configuring Watlow
controllers.
zero cross — Action that provides output switch-
ing only at or near the zero-voltage crossing points
of the ac sine wave. See burst fire.
zero switching — See zero cross.
A . 4 ■ A p p e n d i x Wa t l o w S e r i e s F 4 S / D