Watlow F4T

Watlow F4T • 135 • Chapter 5 Function Reference
Note:
The type of field device connected to the output determines how frequently it can be
switched.
Options:
• Fixed Time Base: the percent output power is converted to a duty cycle over the Fixed
Time Base. For example, if the Fixed Time Base is ten seconds and 75% power is called
for, the output turns on for 7.5 seconds and off for 2.5 seconds, and repeats as illus-
trated below. This is appropriate for mechanical relays.
• Variable Time Base: the output switches as often as every three ac line cycles. For
example, when 66% power is called for, the output is on for six ac cycles and off for
three, and when 50% power is called for, the output is on for three ac cycles and off
for three. This method is appropriate for solid-state relays but not for electromechani-
cal relays, mercury displacement relays, inductive loads or heaters with unusual resis-
tance characteristics.
Fixed Time Base
Set the duration of one on-off cycle. This applies when the Time Base Type is set to Fixed
Time Base.
Range: 0.1 to 60.0 seconds
Low Power Scale
Set the minimum power level for the output. When the
input equals 0% (off), the output is equal to the value
set here. When the input equals 100% (on), the output is
equal to the value set with High Power Scale. Values be-
tween 0% and 100% are scaled proportionally. See the il-
lustration to the right.
Range: 0.0 to 100.0%