AERCO BMK 2.0 LN for Mass. only - Manual (Page 20)

2-8
shield is to be connected only to the terminals
labeled SHEILD 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.
2.7.2 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 and must be similar to AERCO
BALCO wire sensor P/N 12449. A resistance
chart for this sensor can be found in APPENDIX
C.
2.7.3 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
PMC Board located inside the Control Box.
Contact the AERCO factory for information on
setting DIP switches.
All supplied signals must be floating
(ungrounded) signals. Connections between the
source and the Boiler’s I/O Box must be made
using twisted shielded pair of 18 –22 AWG wire
such as Belden 9841(see Fig. 2.9). Polarity
must be maintained and the shield must be
connected only at the source end and must be
left floating (not connected) at the Boiler’s I/O
Box.
Whether using voltage or current for the drive
signal, they are linearly mapped to a 40° to
240°F setpoint or a 0% to 100% firing rate. No
scaling for these signals is provided
2.7.4 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.
2.7.5 SHIELD
The SHIELD terminals are used to terminate any
shields used on sensor wires connected to the
unit. Shields must only be connected to these
terminals.
2.7.6 mA OUT
These terminals provide a 4 to 20 mA output
that can be used to monitor setpoint ( 40
o to
240 o F), outlet temperature (30 o to 240 o F), or fire
rate (0% to 100%). This function is enabled in
the Configuration Menu (Chapter 3, Table 3.4).
2.7.7 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 or other suitable device.
2.7.8 EXHAUST SWITCH IN
These terminals permit an external exhaust
switch to be connected to the exhaust manifold
of the boiler. The exhaust sensor should be a
normally open type switch (such as AERCO Part
No. 123463) that closes (trips) at 500
o F.
2.7.9 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 (Fig. 2.9). The
wiring terminals for these interlocks are located
inside the I/O Box on the unit front panel. The
I/O Box cover contains a wiring diagram which
shows the terminal strip locations for these
interlocks labeled REMOTE INTL’K IN and
DELAYED INTL’K IN. Both interlocks, described
below, are factory wired in the closed position.