34 WATLOW Series 965 User's Manual Appendix
Glossary, A-P
This glossary includes general thermal system control terms.
Alarm: A condition, generated by a controller,
indicating that the process has exceeded or fallen
below the set or limit point.
Alarm Silence: Disables the alarm relay output.
Anti-reset: Control feature that inhibits automatic
reset action outside the proportional band.
Automatic prompts: Data entry points where a
microprocessor-based control "prompts" or asks
the operator/programmer for information input.
Auto-tune: Automatically tunes the Series 965
PID parameters to fit the characteristics of your
particular thermal system.
Bumpless transfer: When transferring from auto
to manual operation, the control output(s) will not
change ("bumpless," smooth transition).
Closed loop: Control system that has a sensing
device for process variable feedback.
Cold junction: Point of connection between
thermocouple metals and the electronic instrument.
Cold junction compensation: Electronic means
to compensate for the effective temperature at the
cold junction.
Cycle time: The time necessary to complete a full
on-through-off period in a time proportioning control
system.
Derivative: Anticipatory action that senses the
rate of change of the process, and compensates to
minimize overshoot and undershoot. Also "rate."
Deviation alarm: An alarm referenced at a fixed
number of degrees, plus or minus, from set point.
Default parameters: The parameters, or program-
med instructions, permanently stored in micropro-
cessor software to provide a data base.
DIN: Deutsche Industrial Norms, a widely-recog-
nized German standard for engineering units.
Display capability: In a digital indicating instru-
ment, the entire possible span of a particular
parameter or value.
Droop: Difference in temperature between set
point and stabilized process temperature.
Duty cycle: Percentage of "load on time" relative
to total cycle time.
Hysteresis: In on/off control, the temperature
change necessary to change the output from full on
to full off.
Hunting: Oscillation or fluctuation of process tem-
perature between set point and process variable.
Input: Process variable information being supplied
to the instrument.
Integral: Control action that automatically elimi-
nates offset, or “droop,” between set point and
actual process temperature. Also "reset."
Isolation: Electrical separation of sensor from
high voltage circuitry. Allows for application of
grounded or ungrounded sensing element.
JIS: Joint Industrial Standards. Also Japanese
Industrial Standards Committee (JISC). Estab-
lishes standards on equipment and components.
Offset: Adjustment to actual input temperature and
to the temperature values the Series 965 uses for
display and control.
On/off control: Control of temperature about a set
point by turning the output full on below set point
and full off above set point in the heat mode.
Open loop: Control system with no sensory
feedback.
Output: Action in response to difference between
set point and process variable.
Overshoot: Condition where temperature exceeds
set point due to initial power up or process
changes.
P control: Proportioning control.
Parameter: A physical property whose value
determines the response of an electronic control to
given inputs.
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