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Benchmark 2500DF-3000DF Installation, Operation & Maintenance Manual
2.10.9 RS485 Comm (+, GND, & -)
The RS485 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 (RS485)
communication.
2.10.10 RS232 Comm (TxD & RxD)
The RS232 communication terminals permit a laptop computer or other suitable terminal to be connected
to the boiler. The RS232 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 (REMOTE INTL'K IN and DELAYED INTL'K IN in Figure 2-12). Both
interlocks, described below, are factory wired in the closed position (using jumpers).
Both the Delayed Interlock and Remote Interlock must be in the
closed position for the unit to fire.
Remote Interlock In (OUT & IN)
2.10.12.1
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).
Delayed Interlock In (OUT & IN)
2.10.12.2
The Delayed Interlock terminals can be used in one of two ways:
•
In conjunction with the optional external sequencing valve (see section 2.14 and Chapter 10 –
BST), a component of AERCO's on-board Boiler Sequencing Technology (BST) solution. By
default a cable of the boiler's wiring harness is connected to these terminals. If BST is
implemented, the other end of that cable is connected to the sequencing valve.
•
If BST is NOT implemented, the second use is typically 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. 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.
To use this option, you must disconnect the harness from the Delayed Interlock terminals and
connect the proving device in its place.
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).
2.10.13 Fault Relay (NC, COM, & NO)
The fault relay is a single pole double throw (SPDT) relay having a normally open and normally closed set
of relay contacts that are rated for 5 amps at 120 VAC and 5 amps at 30 VDC. The relay energizes when
OMM-0099_0A
GF-145
CHAPTER 2 – INSTALLATION
NOTE
AERCO International, Inc. • 100 Oritani Dr. • Blauvelt, NY 10913
Ph.: 800-526-0288
Page 29 of 234
PR1: 05/21/2014
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