Watlow Series 935A User’s Manual
4 7
Ready Acknowledge
A Series 935A 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
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.
Remote Set Point
A 0-5V
Î
(dc) input from another controller or other source.
RTD
Resistive Temperature Detector. A sensor whose resistance in-
creases with increasing temperature.Set Point
The desired process value programmed into a control.
Signal
Any electrical transmittance that conveys information.
Signal OFF
A Series 935 timer output (Output 2) choice that toggles the out-
put OFF, then ON at the end of the countdown timer cycle for a
period equal to the signal time.
Signal ON
A Series 935 timer output (Output 2) choice that toggles the out-
put 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 com-
plete 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 trans-
fer medium, sensing device, a control instrument, and a redun-
dant control device (limit).
Thermocouple
A temperature sensing device made by joining two dissimilar met-
als. 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 stabi-
lizing.
