Watlow Series 935B - Manual (Page 46)

46 Watlow Series 935B User’s Manual
Glossary
Alarm
A condition, generated by the controller,
indicating that the process has exceeded or
fallen below the set or limit point.
Alarm Hysteresis
A change in the process variable required to re-
energize the alarm output.
Ambient Temperature
Temperature surrounding the components of a
thermal system.
Auto-tune
Automatically sets PID values to fit a particular
thermal system.
Bumpless Transfer
When transferring from auto to manual
operation, the control output(s) will maintain the
same output level.
Calibration
Adjusting an instrument to a known value.
Configuration Menu -The second software sub
menu of the Series 935B Operations Menu;
provides a location to set inputs, ranges, output
types, alarm type, timer function, failure mode,
and lockout types.
Control Mode
The method of control, i.e. ON/OFF, time
proportioning, PI, PID or manual.
Cycle Time
Time required for a control to complete one ON
through OFF cycle.
Dead Band
Adjusts the effective cool set point above the
primary set point by the dead band value in
degrees. In cool/heat applications, dead band
prevents continuous cool output action by
creating a buffer between heating and cooling
output action.
Delay OFF
A Series 935B timer output (Output 2) choice
that turns the output OFF at the end of the
countdown timer time.
Delay ON
A Series 935B timer output (Output 2) choice
that turns the output ON at the end of the
countdown timer time.
Derivative
Limits the rate of change of the process to
eliminate overshoot in slow or lagging loads
(de=ra).
Deviation Alarm
An offset value which tracks the set point.
Process changes beyond this value register an
alarm condition.
DIN-a-mite ®
Watlow family of DIN rail-mounted SCR power
controllers.
Droop
The difference between the set point and actual
values once the system stabilizes.
Hysteresis
A change in the process variable required to re-
energize the control or alarm output.
Idle Set Point
Desired control value before and after timing
period.
Integral
Accumulates error to eliminate offset or droop
(It=1/re).
Local Set Point
Primary set point, not remote.
ON/OFF
Control by turning the output full ON until set
point is reached, and then turning OFF until the
process error exceeds the hysteresis.
Operations Menu
Series 935B software menu; provides a location
to start auto-tune, set alarm points, set
countdown time, choose an idle or normal set
point type, choose a local or remote set point
input, and to go to the PID or Configuration
Menus.
Overshoot
The amount a process variable exceeds set
point before stabilizing.
Percent Power Control
Open loop control with output power set at a
particular level.
PID
(Proportional, Integral, Derivative). A control
mode: proportional action sets the system, inte-
gral reduces droop, derivative reduces over-
shoot and undershoot.
PID Menu
The first software sub menu of the Series 935B
Operations Menu; provides a location to
manually set values for proportional band,
hysteresis, cycle time, integral, derivative, and
calibration offset.
Process Alarm
A fixed value independent of set point. Process
changes beyond this value register an alarm
condition.
Process Error
The difference between the set point and the
actual process.
Proportional
Output effort proportional to the error from set
point. If the proportional band is 20° and the
process is 10° below set point, the heat
proportioned effort is 50%. The lower the Pb
value, the higher the gain.
Proportional Band
A range in which a control’s proportioning
function is active (See PID).
Range
The area between two limits in which a quantity
or value is measured. Usually expressed in
terms of lower and upper limits.
Ready Acknowledge
A Series 935B countdown timer start choice that
pre-initiates the timer with a down key press,
and then starts it with a SET press when the
actual temperature is within the Ready Band.
Ready Band
Thermal area above and below primary set point
in which the timer will count down.
Relay, Electromechanical
A power switching device that completes or
interrupts a circuit by physically moving electrical
contacts. Not recommended for PID control.
RTD
Resistive Temperature Detector. A sensor whose
resistance increases with increasing
temperature.
Remote Timer Start
Activation of the timer functions using an
external remotely mounted switch connected to
the 935B RTS input.
Set Point
The desired process value programmed into a
control.
Signal
Any electrical transmittance that conveys
information.
Signal OFF
A Series 935B timer output (Output 2) choice
that toggles the output OFF, then ON at the end
of the countdown timer cycle for a period equal
to the signal time.
Signal ON
A Series 935B timer output (Output 2) choice
that toggles the output ON, then OFF at the end
of the countdown timer cycle for a period equal
to the signal time.
Signal Time
Time duration the timer output will turn ON or
OFF after a complete timing period.
SCR
Silicon controlled rectifier. A solid state device, or
thyristor, with no moving parts, that is used in
pairs to control AC voltages within one cycle.
SCRs control voltage from a power source to the
load by burst firing (also called zero-cross firing)
or phase angle firing.
SSR
Solid State Relay. A solid state switching device
that switches current ON and OFF. It has no
moving parts.
Thermal System
A regulated environment consisting of a heat
source, heat transfer medium, sensing device, a
control instrument, and a redundant control
device (limit).
Thermocouple
A temperature sensing device made by joining
two dissimilar metals. This junction produces an
electrical voltage in proportion to the difference
in temperature between the hot junction and
lead wire connection to the sensing device (cold
junction).
Undershoot
The amount a process variable falls below set
point before stabilizing.