SECTION 5 DE-18 USER MANUAL
57
21. This documentation describes the intercom-
munications of multiple units hooked
together through their EMS547's Port 4
(RS232)(Converted to RS485 and accessi-
ble on the front of the panel via two special
connectors labeled "Sequencing Ports"). A
customer- supplied cable connects the Mas-
ter and Slave units.
S
LAVE COMMUNICATIONS OPERATIONS
The Unit's Slave Operations are valid while the
Master Communications Enable (S-9 adjustment)
select is set to "NO".
When a Unit's Slave Communications Address (S-8
adjustment) is set to "Independent" the unit will not
follow remote commands given to it by the master.
This being said it is still a good idea to power down
the unit before working on the equipment.
When the Unit's Slave Communications Address (S-
8 adjustment) is set to Slave #X the Master will treat
this unit as it's Slave #X. Each Slave must be set to a
sequentially unique address.
5.4.3.3 Master Communications Operations The
Unit's Slave Operations are disabled when the
Master Communications Enable (S-9 adjustment)
select is set to "YES".
The Master Unit's Slave Communications Address
(S-9 adjustment) will be set to the number of Slaves it
will control, not including itself. The Master Unit's will
be addressed as the last Unit.
Example: If there is one Master Unit and 3 Slave
Units, set the Master's Slave Communications
Address (S-8 adjustment) to SLV#3. This will cause
the Master Unit to be treated as the 4th Slave Unit.
The Master will control all of the slaves that have not
been locally started by the Start Pushbutton, and it
will regain control when the unit is locally stopped by
the Stop Pushbutton.
M
ASTER/SLAVE START/STOP OPERATIONS.
All Units may still be started and stopped via each
panel's pushbuttons. This will start and stop the local
control of the unit. If a Unit is setup as a Slave with
the Slave Communications Address (S-8 adjustment)
set to “Independent this is also the only way to start
and stop the unit. Also, while a Unit is under local
control the Master may not start and stop the unit.
The P2 Pressure being below the Load Pressure
setpoint (S~14 adjustment) will start the first unit.
After one unit is loaded, additional units may be
started if the Load RPM% of all of the loaded units
rises above the Increase Demand% set-point (S-10
adjustment) for the Demand "+" Delay time (S-11
adjustment). The units are added indirectly by P2 as
the demand effects the Load RPM%.
Until only one unit is loaded additional units may be
stopped if the Load RPM% of all of the loaded units
fall below the Decrease Demand% setpoint (S-10
adjustment) for a fixed 120 seconds. The P2
Pressure being above the Unload Pressure setpoint
(S-13 adjustment) for a fixed 120 seconds will stop
the first unit. The units are subtracted indirectly by P2
as the demand affects the Load RPM%.
Special condition, if a Slave looses communications,
not configured for Independent operation, it will
subject to an override start. If the P2 pressure drops
below the P2 OVRD STRT setpoint (S-15
adjustment) a start will be initiated. The Stop button
can stop this override start unless the P2 pressure is
still below the override pressure in which case the
unit may start when you release the stop button. If
stop is desired you may enter the S-#'s to change the
“Slave" to "Independent" and then press the stop
button. If a unit must remain off while being used as a
Slave press the ESD button or disable the remote
starting of the Slave by changing the Slave address
to ~lndependent and cycling the ESD button (in and
then out).
The Master Unit controls an internal sequencing list
that arranges the order of the units that are called to
run. As units are made available, they are added to
the end of the sequencing list. As units are made
unavailable through shutdowns or being locally
started, they are removed from the sequencing list
and the other units shift towards the first (Lead Unit)
position. When the Master first powers up, the units
are arranged in the sequence list as the Master
communicates to each Slave. As this is happening,
the availability from the slaves will not have been
read yet and for this reason the Master will insert
itself at the top of the list, then the slaves will be
appended to the end of the list as they are
recognized as being available. As the last unit is
stopped, the sequencing list is modified to even out
the wear on the units. The first (Lead Unit) position is
WARNING
Only One Unit Should Be Selected As Master
For Correct Operation.
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