Control Via Modbus (Through Bcm); Operating Scenario; Physical Modbus Rs485 Wiring - Watts AERCO EXT Installation, Operation & Maintenance Manual

Ufly Controller and BCM for Modulex EXT
CHAPTER 6: BOILER COMMUNICATIONS MODULE (BCM)

6.5 Control Via Modbus (Through BCM)

All Modbus Networks are implemented utilizing a "Manager-Client" scenario where only one
device, the "Manager", can initiate a communication sequence. However, BCMs can only function
as "Client" devices on a Modbus Network. Therefore, the BCM must be interfaced to an external
controlling "Manager". The "Manager" can be the AERCO Control System (ACS), or an Energy
Management System (EMS)/Building Automation System (BAS) developed by other
manufacturers.
The following sections provide describe Modbus Network operation and required wiring
connections between the BCM "Clients" and the controlling "Manager" (EMS, BAS).

6.5.1 Operating Scenario

An EMS or BAS Master can control the Networked Modulex Boilers utilizing Remote Setpoint. An
AERCO ACS Master can control the networked Modulex boilers utilizing a Modbus signal.
If the external control signal from the Master ACS, EMS, or BAS is lost, the BCM will assume
control of the Modulex Boilers, if enabled. When this occurs, the BCM will maintain the boiler at a
constant setpoint (See section 6.3) In addition, the BCM Fault Relay will be activated and the red
Fault LED (DL2) will light.

6.5.2 Physical Modbus RS485 Wiring

Modbus RS485 devices should be wired in a "Daisy-Chain" configuration similar to the example
shown below. DO NOT wire the units in a "Star" configuration where all devices are connected to
a central point (node).
MASTER
SLAVE
SLAVE SLAVE SLAVE
SLAVE
#1
#3 #4 #5
#2
Figure 6-11: Typical Daisy-Chain Modbus/RS485 Network
The physical wiring connections for a Modbus Network should be made using shielded twisted-
pair wire, from 18 to 24 AWG (e.g. Belden # 9841, #8761, #3105A, or equivalent).
Modbus wiring connections are made at terminals 1 and 2 of BCM connector Y2 in the
Input/Output box as shown in Figure 6-12.
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