Watlow MICRODIN - Manual (Page 95)

a form A or form B contact.
hysteresis — A change in the process variable required to re-energize the
control or alarm output. Sometimes called switching differential.
integral — Control action that automatically eliminates offset, or droop,
between set point and actual process temperature. See auto-reset.
integral control (I) — A form of temperature control. 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.
junction, cold — Connection point between thermocouple metals and the
electronic instrument. See junction, reference.
junction, reference — The junction in a thermocouple circuit held at a stable,
known temperature (cold junction). Standard reference temperature is 32°F
(0°C).
Modbus ™ — A digital communications protocol owned by AEG Schneider
Automation for industrial computer networks.
Modbus ™ RTU — Remote Terminal Unit, an individual Modbus ™ -capable device
on a network.
NEMA 4X — A NEMA specification for determining resistance to moisture
infiltration. This rating certifies the controller as washable and corrosion
resistant.
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 variable exceeds the set point
before it stabilizes.
P control — Proportioning control.
PD control — Proportioning control with derivative (rate) action.
PDR control — Proportional derivative control with manual reset, used in fast
responding systems where the reset causes instabilities. With PDR control, 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 undershoot.
proportional — Output effort proportional to the error from set point. For
example, if the proportional 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. Expressed in units, degrees or percent of span. See PID.
Wa t l o w M i c r o D I N A . 9
Appendix