AERCO BMK 3.0 LN Nat. Gas APRIL 2009 - Manual (Page 19)

INSTALLATION
2-9
The factory default for the outdoor sensor is
DISABLED. To enable the sensor and/or select
an enable/disable outdoor temperature, see the
Configuration menu in Chapter 3.
The outdoor sensor may be wired up to 200 feet
from the boiler. It is connected to the
OUTDOOR SENSOR IN and SENSOR
COMMON terminals in the I/O Box (see Figures
2-10 and 2-11). Wire the sensor using a twisted
shielded pair wire from 18 to 22 AWG. There is
no polarity to observe when terminating these
wires. The shield is to be connected only to the
terminals labeled SHIELD in the I/O Box. The
sensor end of the shield must be left free and
ungrounded.
When mounting the sensor, it must be located
on the North side of the building where an
average outside air temperature is expected.
The sensor must be shielded from direct sunlight
as well as impingement by the elements. If a
shield is used, it must allow for free air
circulation.
2.10.2 AUX SENSOR IN
The AUX SENSOR IN terminals can be used to
add an additional temperature sensor for
monitoring purposes. This input is always
enabled and is a view-only input that can be
seen in the Operating Menu. The sensor must
be wired to the AUX SENSOR IN and SENSOR
COMMON terminals and must be similar to
AERCO BALCO wire sensor Part No. 12449. A
resistance chart for this sensor is provided in
Appendix C.
2.10.3 ANALOG IN
The ANALOG IN + and – terminals are used
when an external signal is used to drive the
firing rate (Direct Drive Mode) or change the
setpoint (Remote Setpoint Mode) of the Boiler.
Either a 4 to 20 mA /1 to 5 VDC or a 0 to 20 mA
/ 0 to 5 VDC signal may be used to vary the
setpoint or firing rate. The factory default setting
is for 4 to 20 mA / 1 to 5 VDC, however this may
be changed to 0 to 20 mA / 0 to 5 VDC using the
Configuration Menu described in Chapter 3. If
voltage rather than current is selected as the
drive signal, a DIP switch must be set on the
CPU Board located inside the Control Box.
Contact the AERCO factory for information on
setting DIP switches.
All of the supplied signals must be floating
(ungrounded) signals. Connections between the
signal source and the Boiler’s I/O Box must be
made using twisted shielded pair wire from 18 to
22 AWG, such as Belden 9841 (see Figure
2-11). Polarity must be maintained. The shield
must be connected only at the source end and
must be left floating (not connected) at the
Boiler’s I/O Box.
Regardless of whether voltage or current is used
for the drive signal, they are linearly mapped to
a 40°F to 240°F setpoint or a 0% to 100% firing
rate. No scaling for these signals is provided
2.10.4 B.M.S. (PWM) IN
NOTE
Only BMS Model 168 can utilize Pulse
Width Modulation (PWM), not the BMS II
(Model 5R5-384).
These terminals are used to connect the
AERCO Boiler Management System (BMS)
Model 168 to the unit. The BMS Model 168
utilizes a 12 millisecond, ON/OFF duty cycle.
This duty cycle is Pulse Width Modulated (PWM)
to control firing rate. A 0% firing rate = a 5% ON
pulse and a 100% firing rate = a 95% ON pulse.
2.10.5 SHIELD
The SHIELD terminals are used to terminate any
shields used on sensor wires connected to the
unit. Only shields must be connected to these
terminals.
2.10.6 mA OUT
These terminals provide a 4 to 20 mA output to
the VFD to control the rotational speed of the
blower. This function is enabled in the
Configuration Menu (Chapter 3, Table 3.4).
2.10.7 RS-485 COMM
These terminals are used for RS-485 MODBUS
serial communication between the unit and an
external “Master” such as a Boiler Management
System (BMS), Energy Management System
(EMS), Building Automation System (BAS) or
other suitable device.
2.10.8 EXHAUST SWITCH IN
These terminals permit an external exhaust
switch to be connected to the exhaust manifold
of the boiler. The exhaust switch should be a
normally open type switch (such as AERCO Part
No. 123463) that closes (trips) at 500°F.
2.10.9 INTERLOCKS
The unit offers two interlock circuits for
interfacing with Energy Management Systems
and auxiliary equipment such as pumps or
louvers. These interlocks are called the Remote
Interlock and Delayed Interlock (Figure 2-11).
The wiring terminals for these interlocks are