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Benchmark 750-3000 Boiler Installation & Startup Manual
SECTION 2 – INSTALLATION
2.11.2 AIR TEMP SENSOR
The AIR TEMP SENSOR terminal is used to monitor the air inlet temperature sensor (P/N
123449). This input is always enabled and is a "view only" input. It can be seen in the AIR
TEMP setting in the Operating menu (see Section 2.4: OPERATING Menu, item 4, of the
Benchmark 750 – 3000 Operation and Maintenance Guide, OMM-0122 (GF-206). A resistance
chart for this sensor is provided in APPENDIX C of the same guide. This sensor is an active part
of the combustion control system and must be operational for accurate air/fuel mixing control.
2.11.3 O
SENSOR (+ & –)
2
The two O
SENSOR terminals (+ and –) are used to connect an integrated oxygen sensor to
2
the I/O board. The O
concentration is displayed in the Operating menu after a 60 second warm-
2
up period. See Section 2.4: OPERATING Menu, item 13, of the Benchmark 750 – 3000
Operation and Maintenance Guide, OMM-0122 (GF-206).
2.11.4 SPARK SIGNAL (+ & –)
The two SPARK SIGNAL terminals (+ & -) connect to the spark monitor (P/N 61034, also called
"AC Current transducer"), which monitors the current going to the ignition transformer (P/N
65085. See Section 4.12 in the Benchmark 750 – 3000 Operation and Maintenance Guide,
OMM-0122 (GF-206) for more information. If the current is insufficient (too high or low) during
the ignition sequence, the controller will abort the ignition cycle. The controller will attempt up to
three ignition cycles. If the current is insufficient by the third try, the controller will shut down and
display a fault message.
2.11.5 ANALOG IN
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 – 5 VDC or a 0 to 20 mA/0 – 5 VDC signal may be used to vary the set-
point or air/fuel valve position. The factory default setting is 4 to 20 mA/1 to 5 VDC, however
this may be changed to 0 to 20 mA/0 – 5 VDC in the Configuration menu; see Section 2.6:
CONFIGURATION Menu, item 6, in the Benchmark 750 – 3000 Operation and Maintenance
Guide, OMM-0122 (GF-206).
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 Controller. 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 board (Figure 2-11) 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 board.
Whether using voltage or current for the drive signal, they are linearly mapped to a 40°F to
240°F (4.4 to 116 °C) setpoint or a 0% to 100% air/fuel valve position. No scaling for these
signals is provided
2.11.6 VALVE FEEDBACK
The two VALVE FEEDBACK terminals (+ and –) are used when the Sequencing Isolation Valve
Feedback option is selected. The Valve Feedback signal is connected to the "Valve Fdbk"
terminals and is used to confirm that the valve has properly opened or closed. If the Valve
OMM-0121_D • GF-205 • 5/9/2019
Technical Support • (800) 526-0288 • Mon-Fri, 8 am - 5 pm EST
Page 36 of 122
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