Watlow Series 982 User Manual download pdf (Page 132)

A.2 WATLOW Series 982 User’s Manual

Appendix

annunciator — A visual display that uses pilot lights to

indicate the former or existing condition of several items

in a system.

burst fire — A power control method that repeatedly

turns on and off full ac cycles. Also called zero-cross

fire, it switches close to the zero-voltage point of the ac

sine wave. Variable-time-base burst fire selectively

holds or transits ac cycles to achieve the desired power

level. See zero cross.

calibration offset — An adjustment to eliminate the dif-

ference between the indicated value and the actual

process value.

closed loop — A control system that uses a sensor to

measure a process variable and makes decisions based

on that feedback.

cold junction — see junction, cold.

cold junction compensation — Electronic means to

compensate for the effective temperature at the cold

junction.

default parameters — The programmed instructions

that are permanently stored in the microprocessor soft-

ware.

derivative — The rate of change in a process variable.

Also known as rate. See PID.

derivative control (D) — The last term in the PID con-

trol algorithm. Action that anticipates the rate of change

of the process, and compensates to minimize overshoot

and undershoot. Derivative control is an instantaneous

change of the control output in the same direction as the

proportional error. This is caused by a change in the

process variable (PV) that decreases over the time of

the derivative (TD). The TD is in units of seconds.

Deutsche Industrial Norm (DIN) — A set of technical,

scientific and dimensional standards developed in

Germany. Many DIN standards have worldwide recogni-

tion.

DIN — See Deutsche Industrial Norm.

droop — In proportional controllers, the difference

between set point and actual value after the system sta-

bilizes.

duty cycle — The percentage of a cycle time in

which the output is on.

external transmitter power supply — A dc

voltage source that powers external devices.

filter, digital (DF) — A filter that slows the

response of a system when inputs change unre-

alistically or too fast. Equivalent to a standard

resistor-capacitor (RC) filter.

form A — A single-pole, single-throw relay that

uses only the normally open (NO) and common

contacts. These contacts close when the relay

coil is energized. They open when power is

removed from the coil.

form B — A single-pole, single-throw relay that

uses only the normally closed (NC) and com-

mon contacts. These contacts open when the

relay coil is energized. 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.

hysteresis — A change in the process variable

required to re-energize the control or alarm out-

put. 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 —Joint Industrial Standards (JIS) A

Japanese agency that establishes and main-

tains standards for equipment and components.

Also known as JISC (Japanese Industrial

Standards Committee), its function is similar to

Germany’s Deutsche Industrial Norm (DIN).

Glossary, A-J

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