AERCO BMK 3.0 LN Natural Gas July 2011 - Manual (Page 21)

INSTALLATION
2-9
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 AIR SENSOR IN
The AIR SENSOR IN is connected to the AUX
SENSOR IN and SENSOR COMMON terminals
on the I/O board. The AIR SENSOR measures
the temperature of the air input to the Air/Fuel
Valve. This temperature reading is one of the
components used to calculate the rotational
speed of the blower used in the combustion
Calibration process (Chapter 4).
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
PMC 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.
IMPORTANT
DO NOT USE the mA OUT output to
remotely monitor Setpoint, Outlet Temp or
Fire Rate Out.
2.10.6 mA OUT
These terminals provide a 4 to 20 mA output to
the VFD (if so equipped) to control the rotational
speed of the blower. This function is enabled in
the Configuration Menu (Chapter 3, Table 3-4).
2.10.7 0 – 10V OUT
These terminals provide a 0 to 10V output to
control the rotational speed of the blower. This
function is enabled in the Configuration Menu
(Chapter 3, Table 3-4).
2.10.8 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.