Benchmark 750/1000 Boiler
Installation, Operation & Maintenance Manual
CHAPTER 2 – INSTALLATION
OMM-0082_0J
AERCO International, Inc.
•
100 Oritani Dr.
•
Blauvelt, NY 10913
Page
29
of
192
GF-130
Ph.: 800-526-0288
05/21/2014
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 COMBUSTION AIR Terminal
The COMBUSTION AIR terminal is used to monitor the combustion air temperature sensor.
This input is always enabled and is a “to view only” input that can be seen in the operating
menu. The sensor is an AERCO BALCO wire sensor P/N 12449. A resistance chart for this
sensor is provided in APPENDIX C. This sensor is an active part of the combustion control
system and must be operational for accurate air/fuel mixing control.
2.10.3 O
2
SENSOR Terminals
The O
2
SENSOR (+) and O
2
SENSOR (–) terminals are used to connect an external oxygen
sensor to the I/O Box. The O
2
concentration is displayed in the operating menu of the C-More
Control system after a 60 second warm-up period.
2.10.4 SPARK SIGNAL Terminals
The two SPARK SIGNAL terminals (+ & -) permit an external current sensor to be connected for
ignition spark monitoring purposes. If no spark is present during the ignition sequence, the
controller will shut down and display a fault message.
2.10.5 ANALOG IN Terminals
The two ANALOG IN terminals (+ and –) are used when an external signal is used to 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 set-
point or air/fuel valve position. 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 C-More 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 (see Figure 2-12) must be made using twisted shielded pair of 18–22
AWG wire such as Belden 9841. 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°F to
240°F setpoint or a 0% to 100% air/fuel valve position. No scaling for these signals is provided
2.10.6 B.M.S. (PWM) IN Terminals
These terminals are only used to connect TO the legacy AERCO Boiler Management System
(BMS), which utilize a 12 millisecond, ON/OFF duty cycle and is Pulse Width Modulated (PWM)
to control valve position. A 0% valve position = a 5% ON pulse and a 100% valve position = a
95% ON pulse. Note that these connections cannot be used with the AERCO Control System
(ACS).
2.10.7 SHIELD Terminals
The two SHIELD terminals are used to terminate any shields used on sensor wires connected to
the unit. Shields must only be connected to these terminals.
