Air Temp Sensor; Sensor (+ & -); Spark Signal (+ & -); Analog In - Watts AERCO Benchmark BMK750 Installation And Start-Up Manual

Benchmark 750-6000 with Edge [i]: Install-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 BST
Main Menu → Advanced Setup → BST Cascade
Outdoor Temp parameter in the
Configuration menu. A resistance chart for this sensor is provided in Section 6 of the
Benchmark 750-6000 with Edge [i] Controller Reference Guide (OMM-0146, GF-219). 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
SENSOR terminals (+ and –) are used to connect an integrated oxygen sensor to
The two O
2
Main Menu → Calibration →
the I/O board. The O concentration is displayed in the
2
Input/Output → O2 Sensor
menu after a 60 second warm-up period.
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). 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 operating 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 setpoint
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 Main Menu → Advanced Setup → Unit → Unit
Application Configuration menu.
If voltage rather than current is selected as the drive signal, a DIP switch must be set on the PMC
Board located inside the 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
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:
OMM-144_B • GF-217 • Technical Support • (800) 526-0288 • Mon-Fri, 8 am - 5 pm EST
5/25/2020 Page 39 of 62