Air Temp Sensor Terminals; O 2 Sensor Terminals (O2+ & O2-); Spark Signal Terminals; Analog In Terminals - Watts Aerco BENCHMARK 750 User Manual

Benchmark 750 – 1000 Boiler User Manual - INTERNATIONAL

2.10.2 AIR TEMP SENSOR Terminals

The AIR TEMP SENSOR terminals are used to monitor the air inlet temperature sensor (P/N
61024). This input is always enabled and is a "to view only" input that can be seen in the
Operating menu. 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 SENSOR Terminals (O2+ & O2-)
2
The O SENSOR (+) and O
2
sensor to the I/O Box PCB. The O
More Control system after a 60 second warm-up period.

2.10.4 SPARK SIGNAL Terminals

The 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 7.12). 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.

2.10.5 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 Heating 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 Heating Boiler's I/O PCB (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 con-
nected only at the source end and must be left floating (not connected) at the Heating Boiler's
I/O PCB.
Whether using voltage or current for the drive signal, they are linearly mapped to a 40°F to
240°F (4.4 °C to 116 °C) setpoint or a 0% to 100% air/fuel valve position. No scaling for these
signals is provided

2.10.6 VALVE FEEDBACK Terminals

The Valve Feedback terminals 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 Feedback signal does not
match the Valve-Open or Valve-Close command for the time defined in the "Valve Fdbk timer"
entry, the controller will proceed as follows:
(a) If the valve fails with the Valve Stuck Open fault, the "Valve Stuck Open" message will be
displayed and the unit will remain active.
(b) If the valve fails with the Valve Stuck Closed fault, the "Valve Stuck Closed" message will
be displayed and the unit will shut down.
OMM-0119_0A
GF-130-I
CHAPTER 2 – INSTALLATION
SENSOR (–) terminals are used to connect an integrated oxygen
2
concentration is displayed in the Operating menu of the C-
2
AERCO International, Inc. • 100 Oritani Dr. • Blauvelt, NY 10913
Ph.: 800-526-0288
Page 27 of 170
11/03/2016