Benchmark 1500 - 2000 Boilers
CHAPTER 2 – INSTALLATION
OMM-0097_0C
AERCO International, Inc.
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100 Oritani Dr.
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Blauvelt, NY 10913
Page
29
of
184
GF-142
Ph.: 800-526-0288
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When 0-10VDC is selected, the voltage output is used by the controller to modulate the
combustion blower via the I/O Box terminals labeled VFD/Blower (Section 2.10.11).
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If “On Board” boiler or Water Heater Management is enabled, the Analog Output
terminals are used to drive the isolation valve, open and closed.
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When the 4-20mA is selected for the Analog Output, the 0-10VDC is disabled at the
VFD/Blower terminals, and the selected output is available at the terminals labeled
Analog /-.
2.10.9 RS-485 Comm (+, GND, & -)
The RS-485 communication terminals are used when the boiler plant is being controlled by an
Energy Management System (EMS) or an AERCO Control System (ACS) using Modbus (RS-
485) communication.
2.10.10 RS-232 Comm (TxD & RxD)
The RS-232 communication terminals permit a laptop computer or other suitable terminal to be
connected to the boiler. The RS-232 communication feature permits viewing or changing of
Control Panel menu options and also provides access to data logs showing fault and sensor log
displays.
2.10.11 VFD/Blower (0-10 & AGND)
These terminals (0-10 & AGND) send an analog signal to control the blower speed. When any
of the 4-20mA options is selected for the Analog Outputs (Section 2.10.8), the output from the
VFD/Blower terminals is disabled.
2.10.12 Interlocks
The unit offers two interlock circuits for interfacing with Energy Management Systems and
auxiliary equipment such as pumps or louvers or other accessories. These interlocks are called
the Remote Interlock and Delayed Interlock (Figure 2-12). Both interlocks, described below, are
factory wired in the closed position (using jumpers).
NOTE
Both the Delayed Interlock and Remote Interlock must be in the
closed position for the unit to fire.
2.10.12.1
Remote Interlock In (OUT & IN)
The remote interlock circuit is provided to remotely start (enable) and stop (disable) the unit
if desired. The circuit is 24 VAC and comes factory pre-wired closed (jumped).
2.10.12.2
Delayed Interlock In (OUT & IN)
The delayed interlock is typically used in conjunction with the AUXILIARY RELAY
CONTACTS described in section 2.10.14. This interlock circuit is located in the purge
section of the start string. It can be connected to the proving device (end switch, flow
switch etc.) of an auxiliary piece of equipment started by the unit’s auxiliary relay. The
delayed interlock must be closed for the boiler to fire. If the delayed interlock is connected
to a proving device that requires time to close (make), a time delay (AUX START ON DLY)
that holds the start sequence of the unit long enough for a proving switch to make (close)
can be programmed.
Should the proving switch not prove within the programmed time frame, the unit will shut
down. The AUX START ON DLY can be programmed from 0 to 120 seconds. This option
is located in the Configuration Menu (Chapter 3).
