Aerco Benchmark 3.0LN Series, Installation, Operation & Maintenance Instructions Manual

Page: 45 / 127

MODE OF OPERATION
5-3
I/O Box. The I/O Box is located on the front
panel of the 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. W hen 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 air/fuel valve position (% open) 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 valve position from 0% to
100%. A 4 mA/1V signal is equal to a 0% valve
position, while a 20 mA /5V signal is equal to a
100% valve position. W hen a 0-20 mA/0-5 Vdc
signal is used, zero is equal to a 0% valve
position.
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
CPU 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.
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.
5.5.1 Direct Drive Field Wiring
The only wiring connections necessary for Direct
Drive mode are connection of the remote signal
leads from the source to the unit’s I/O Box. 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. W hen driving multiple units, each
unit’s wiring must conform to the above.
5.5.2 Direct Drive Startup
Since this mode of operation is factory preset
and the valve position is being externally
controlled, no startup instructions are necessary
.
In this mode, the REMOTE LED will light when
the signal is present.
To operate the unit in manual mode, press the
AUTO/MAN switch. The REMOTE LED will go
off and the MANUAL LED will light.