Watlow 8LS Controller - Manual (Page 120)

112 8LS User’s Guide
Appendix B: 8LS-CP
Probe Burn Off
Carbon Probe Burn Off Requirements:
1. To burn off carbon, excess fresh air is supplied to the end of the
probe.
2. The excess fresh air burning off the carbon will cause the temperature
of the probe to increase. The temperature must be monitored from the
probe internal T/C, so that the maximum temperature of the probe is
not exceeded.
3. The excess fresh air flow requirement is 1 to 2 SCFH.
4. The frequency and length of the burn off may be controlled from a
timer or from a contact.
5. The frequency is normally measured in hours and the amount of time
for the burn off is in minutes.
6. The CP controller PID output must be maintained, so that there is no
change of the enriching gas, due to the misreading of the CP probe
during burn-off.
7. The level of the PID control signal must be maintained following the
burn off cycle to allow the probe to recover before automatic control
is restored.
8. The method of burn-off is determined by the type of furnace.
Burn off Procedures
Continuous Furnace
(In time mode)
Batch Furnace
(in input mode)
Recommended air flow 2 SCFH 1 SCFH
Purge period 5 minutes set by operator Time set by operator
Burn off cycle 3 hours set by operator Cycles with open door
Method of operation 1. Hold enrichment gas at current
level during purge cycle.
2. Monitor carbon probe tempera-
ture with the built in T/C.
1. Disable enrichment gas
during cycle.
2. Monitor carbon probe tem-
perature with the built in T/C.
Set the SP for maximum probe temperature of either 1900 or 2100ºF. The carbon burn off
cycle will stop if temperature exceeds the limit. The burn off will continue when tempera-
ture goes below the limit.