Watlow 8LS Controller - Manual (Page 118)

110 8LS User’s Guide
Appendix B: 8LS-CP
Recommended CP Trim Gas Alarm for Continuous
Applications
When using the 8LS-CP for controlling the gas atmosphere, it is
required to prevent gas from being introduced by the control system
until the temperature is above 1400ºF (760ºC). The 8LS-CP has a
digital output for each carbon input that will be On or Low whenever the
PV of the reference T/C input is between 1400 to 2400ºF. When the PV
is below 1400ºF or above 2400ºF, the digital output will be Off or High.
This output — known as the CP Gas Output — is selectable as one of the
30 digital outputs that are available on the 8LS. There could be more
than one output (up to 4)
— depending on the number of CP inputs. The
setpoint of this output is not adjustable in the field.
To use this output correctly, it must be wired in series with a safety
shutdown temperature device to provide for redundant limit/warning of
the carbonizing gas control system.
Recommended CP Trim Gas Alarm for Batch Applications
When using the 8LS-CP for controlling the gas atmosphere in a batch
furnace, it is required to prevent gas from being introduced by the
control system until the temperature is above 1400ºF (760ºC) and to still
be able to maintain the atmosphere when temperature goes below
1400ºF. This requires that the CP gas alarm output will be maintained
below the 1400ºF limit.
The 8LS-CP gas output of the carbon loop alarm function will be On or
Low whenever the PV of the reference T/C input is between 1400 to
2400ºF. Use the CP gas digital output also for the reference T/C loop
low process alarm digital output. After the PV reaches 1400ºF, it allows
the CP gas output to stay On below 1400ºF, and until the SP of the low
process alarm is exceeded, it will stay On. The lowest setting of the low
process alarm is 900ºF.
If the low process alarm setpoint is exceeded (PV goes below SP), the
CP gas output will turn Off and stay Off until the temperature on the
reference T/C goes above 1400ºF.