DESCRIPTION AND OPERATION
SYSTEM OPERATION
I-E96-117B
2 - 3
The SAC station can be forced to take control of the analog out-
put under three conditions.
1. The MFP module directs the SAC station to bypass mode.
2. The SAC station goes into bypass mode when the auto
bypass option is enabled.
3. The operator forces the SAC station into manual override
mode and controls the analog output (demand output) manu-
ally instead of the CIS module.
The CIS may be removed and replaced without affecting the
station supplied demand output. The demand output is
manipulated by using the membrane pushbuttons located on
the station faceplate. The faceplate bar graphs may be config-
ured to display the demand output value or the two analog
inputs as required by the control application.
The operational difference between bypass and manual over-
ride is how the MFP module communication operates. In
bypass mode, the station deciphers and acts upon all of the
MFP module update messages when communication with the
primary module exists. In manual override, the station deci-
phers the MFP module update message but ignores any
request to transfer to any other operating mode.
The station can only be forced to exit manual override by an
operator action. When the station exits manual override it goes
to bypass mode. The station cannot exit bypass mode and go to
normal mode until the MFP module update message directs
the station to enter normal mode. In normal mode, the MFP
module and CIS module have control of the analog output.
For electric drive control applications, the SAC station provides
a specific manual operating mode. The SAC station asserts a
signal M/A_SELECT when the electric drive option is enabled
and the station is in stand-alone, manual override or bypass
mode. The M/A_SELECT signal forces the electric drive to
respond only to contact inputs. Raise/lower contacts are pro-
vided to change the position of the electric drive. In electric
drive mode, the four to 20-milliamp output signal is disabled.
Analog input values can be displayed on the faceplate bar
graphs.
A SAC station may be removed and inserted under power. The
station configuration in the MFP module continues to operate
even when the SAC station is removed.
