DESCRIPTION AND OPERATION
MODES OF OPERATION
2 - 6
I-E96-117B
®
Initialization
Upon power up, the station enters the initialization operational
mode. Initialization prepares the station hardware for opera-
tion. It starts the watchdog timer and runs a test sequence on
the faceplate displays. The MFP module reads the station
option dipswitch settings and interprets how the station will
operate. After initialization is complete, the station enters the
stand-alone mode of operation.
Stand-Alone Operation
The SAC station enters the stand-alone operational mode after
initialization. It can also enter stand-alone from the normal
operating mode when it loses the communication link with the
MFP module and the auto bypass option is disabled. While in
stand-alone, the SAC station has no input to process control; it
can only monitor the process. The MFP module attempts to
communicate with the SAC station by polling for it every 15
seconds. If the SAC station and MFP module cannot establish
communication, the SAC station remains in stand-alone
unless the operator places it in manual override.
In stand-alone, the CIS module still provides the control out-
put. The SAC station cannot directly control the process but,
the operator can monitor the electric drive position or current
output through the analog inputs. For manual override, the
operator can target the demand output of the SAC station to
the control output value of the CIS module using the output
raise/lower pushbutton. Targeting the control output on the
station gives a smooth transfer of control if the operator desires
to place the station in manual override (demand output
directly from the station). The station exits stand-alone mode
by either operator action (forcing the station to manual over-
ride) or MFP module direction (established communications).
Bypass Operation
In the bypass operational mode, the SAC station drives the
control output (analog output or positions the electric drives
depending on which option is selected by the station dipswitch
settings). The SAC station enters bypass operation if a commu-
nication failure occurs while the SAC station is in normal oper-
ation (auto bypass option enabled) or the MFP module forces
the SAC station into bypass (no communication loss).
If the MFP module shows the associated CIS module analog
output (from function code 80, S28) as bad quality, the SAC
station goes into bypass (no communication loss). The bad
quality detection of the associated CIS module analog output
can be the result of either a primary analog output failure or an
open in the field wiring. If field wiring is the cause of the station
