Watlow Controls 8LS, Руководство пользователя

Страница: 117 / 140

Appendix B: 8LS-CP
8LS User’s Guide 109
CP Control
The temperature control may be accomplished by using a standard
Analog Input/Output loop or it may be installed so that the T/C
Reference Loop of the CP input is the temperature control for the
system. A standard PID control and output function is available from
the T/C Reference Loop.
When using the Carbon Burn Off function, the T/C Reference Loop
should not be used for temperature control.
The carbon probe input loop has a dual closed loop PID output for the
control of the atmosphere. The control may use trim gas or air as control
variables. The reverse action output is connected to the enriching gas
supply valve, and the direct action output is connected to the air supply
valve. The CP Loop PID control outputs are only available when the T/
C Reference Loop is between 1400 to 2400
º
F. Temperatures outside
these limits will set the PID outputs to zero percent output.
Trim Gas Temperature Alarm Output
The 8LS-CP has a digital output, available for each CP input, that is
called the CP Gas Alarm. This output is selectable from the alarm menu
of the CP loop as one of the 1-30 digital outputs available. It will be On
when the temperature of the T/C Reference Loop is between 1400 to
2400
º F. Below or above these limits, the CP gas alarm output is Off.
For batch type furnaces, where the temperature will drop below the
1400
º
F limit of the CP gas alarm, a latching CP gas alarm function is
required. This special latching alarm function is accomplished by
setting a setpoint on the low process alarm of the probe reference
temperature loop. Setting a low alarm setpoint keeps the CP gas alarm
On below 1400
º
F.
The process temperature must first go above 1400
º
F to turn On the CP
gas alarm output, and it will not turn Off until the actual temperature has
gone below the low process alarm setpoint. The lowest setting of the
low process alarm for this feature is 900
º
F. To use this feature, after
selecting a digital output for the CP gas alarm output, select the same
digital output for the reference temperature loop low process alarm
output and set the setpoint of the low process alarm for the desired alarm
warning.
This output could be used to power a Normally Closed solenoid valve
installed in the enriching gas supply line to the trim gas control valve.
As always, an external temperature safety device should be used in
series with the CP gas alarm output.