Watlow 8LS Controller - Manual (Page 121)

Appendix B: 8LS-CP
8LS User’s Guide 113
The figure below describes the typical installation of a carbon burn off
system.
Burn Off Function
The carbon probe burn off function of the 8LS-CP is designed to supply
excess fresh reference air to the outside of the probe assembly. When
the excess air is exited at the end of the probe assembly, it supplies
excess oxygen for the burning off of the built up carbon on the end of
the probe.
The burn off selectable digital output of 1-30 will use an interval timer
with a range setting of 1-255 hours or a selectable digital input of 1-12
for a contact closure to start the burn off procedure. The burn off period
timer range is 1-45 minutes.
While in the burn off function, the Time mode selection for a continuous
furnace, or Input mode for a batch furnace, will determine the control
action of the PID output of the CP Loop.
• In the Time mode, the interval timer will start the burn off and hold
the CP PID control output to the value it was at when the burn off
was started.
• In the Input mode, a contact on a digital input generated by a door
opening, or a switch closure, for instance, can start the burn off. The
CP PID output will be held at the value it was at when the burn off
started.
8LS-CP-1
Carbon probe
T/C
SSR
Solenoid
valve
Solenoid
valve Carbon control
valve
Burn off
digital output
Door open contact
N.O
Demand push-button
N.O
Air
Input
CP/DP PID control
Burn off digital
Optional for batch furnace
N.C.
Enriching gas
Batch furnace