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 1400
º
F (760
º
C). 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 2400
º
F. When the PV
is below 1400
º
F or above 2400
º
F, 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 1400
º
F (760
º
C) and to still
be able to maintain the atmosphere when temperature goes below
1400
º
F. This requires that the CP gas alarm output will be maintained
below the 1400
º
F 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
2400
º
F. Use the CP gas digital output also for the reference T/C loop
low process alarm digital output. After the PV reaches 1400
º
F, it allows
the CP gas output to stay On below 1400
º
F, and until the SP of the low
process alarm is exceeded, it will stay On. The lowest setting of the low
process alarm is 900
º
F.
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 1400
º
F.
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