Watlow Series 988 - Manual (Page 142)

WATLOW Series 988 User’s Manual 9.5 Enhanced Software Features, Chapter 9
Enhanced Software
Sample Application
A Series 988 controller is used to heat lube oil to 125°F with a screw-plug-
style heater. To protect the oil from breaking down and maximize its life, it
is desirable to limit the maximum heater sheath temperature to 250° F.
The Series 988 is ordered with two thermocouple inputs. Input 2, the
inner loop in the cascade configuration, measures the heater sheath.
Input 1, the outer loop, measures the lube oil temperature before it leaves
the tank. The external set point is 125°. By setting range high 2 [`rH2] to
250° the set point for the heater sheath will be limited, thus extending the
lube oil life.
Figure 9.5 - Lube oil
tank with cascade
control.
TL W WA
PROCESS
L1 L2 L3 L4
DEV
% OUT DISPLAY
MODE
AUTO
MAN
SERIES 988
input 1
input 2
output 1
limit
limit sensor
oil in
heater
oil out
inner-loop
thermocouple
Lube O il Ta nk
outer-loop
thermocouple