AERCO BMK 3.0 LN Nat. Gas APRIL 2009 - Manual (Page 41)

MODE OF OPERATION
If the Network setting is selected for RS485
Modbus operation, a valid Comm Address must
be entered in the Setup Menu. Refer to Modbus
Communication Manual GF-114 for additional
information.
While it is possible to change the settings of
temperature related functions, the unit is factory
preset with settings that work well in most
applications. It is suggested that an AERCO
representative be contacted, prior to changing
any temperature related function settings. For
descriptions of temperature-related functions
and their factory defaults, refer to Appendices A
and E.
5.4.1 Remote Setpoint Field Wiring
The only wiring connections necessary for the
Remote Setpoint mode are connection of the
remote signal leads from the source to the unit’s
I/O Box. The I/O Box is located on the front
panel of the Benchmark 3.0 Boiler. For either a
4-20mA/0-5V or a 0-20mA/0-5V setting, the
connections are made at the ANALOG IN
terminals in the I/O Box. For a Network setting,
the connections are made at the RS-485 COMM
terminals in the I/O Box. The signal must be
floating, (ungrounded) at the I/O Box and the
wire used must be a two wire shielded pair from
18 to 22 AWG. Polarity must be observed. The
source end of the shield must be connected at
the source. When driving multiple units, each
unit’s wiring must conform to the above.
5.4.2 Remote Setpoint Startup
Since this mode of operation is factory preset
and the setpoint is being externally controlled,
no startup instructions are necessary. In this
mode, the REMOTE LED will light when the
external signal is present.
To operate the unit in the Manual mode, press
the AUTO/MAN switch. The REMOTE LED will
go off and the MANUAL LED will light.
To change back to the Remote Setpoint mode,
simply press the AUTO/MAN switch. The
REMOTE LED will again light and the MANUAL
LED will go off.
5.5 DIRECT DRIVE MODES
The unit’s fire rate can be changed by a remote
signal which is typically sent from an Energy
Management System (EMS) or from a Building
Automation System (BAS). The Direct Drive
mode can be driven by a current or voltage
signal within the following ranges:
4-20 mA/1-5 Vdc
0-20 mA/0-5 Vdc
The factory default setting for the Direct Drive
mode is 4-20 mA/1-5 Vdc. With this setting, a 4
to 20 mA signal, sent by an EMS or BAS is used
to change the unit’s fire rate from 0% to 100%. A
4 mA/1V signal is equal to a 0% fire rate, while a
20 mA /5V signal is equal to a 100% fire rate.
When a 0-20 mA/0-5 Vdc signal is used, zero is
equal to a 0% fire rate.
In addition to the current and voltage signals
described above, the Direct Drive mode can also
driven by a RS485 Modbus Network signal from
an EMS or BAS.
When in a Direct Drive mode, the unit is a slave
to the EMS or BAS and does not have a role in
temperature control. Direct Drive can be used to
drive single, or multiple units.
NOTE
If a voltage, rather than current signal is
used to control the remote setpoint, a DIP
switch adjustment must be made on the
PMC Board located in the Control Box
Assembly. Contact your local AERCO
representative for details.
To enable the Direct Drive Mode, the following
menu setting must be made in the Configuration
Menu:
MENU OPTION SETTING
Boiler Mode Direct Drive
Remote Signal 4-20mA/1-5V,
0-20mA/0-5V, or
Network
Refer to paragraph 3.3 for instructions on
changing menu options.
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