Option 2 Constant Setpoint: Modbus Wired Header Temp Sensor - Watts Aerco Benchmark BMK750 Operation And Service Manual

Benchmark with Edge [I]: Operation-Maintenance Manual
SECTION 7 – BOILER SEQUENCING TECHNOLOGY

Option 2 Constant Setpoint: Modbus Wired Header Temp Sensor

7.3.2
OPTION 2 Instructions: Constant Setpoint with Modbus Wired Header Temp Sensor
OPTION 2 Step 1: MODBUS HEADER TEMP SENSOR WIRING – ANY BOILER
Using the Modbus Transmitter gives the plant the ability to use the Backup manager
feature. This allows any of the client units to become a Backup manager if the manager
unit is not communicating.
1. Connect the Modbus Transmitter terminal Pin B to the RS485+ terminal, and Pin A to the
RS485- terminal on the I/O Board of any Boiler unit, using shielded pair 18 - 22 AWG cable.
2. Connect the Header Temp Sensor to pins 2 and 3 of the Modbus Transmitter using
shielded pair 18 - 22 AWG cable.
3. Install a jumper wire between pins 1 and 2 of the Modbus Transmitter.
NOTES:
•
Polarity must be observed for the RS485 connections.
•
Ground the shield to any SHLD terminal on the I/O Board.
•
The Header Temp Sensor must be installed between 2 and 10 feet (0.61 and 3.1m)
downstream of the last boiler in the plant's supply water header.
•
There is no polarity to be observed. The ground for the shield is at the power supply
ground. The sensor end of the shield must be left free and ungrounded.
HEADER TEMP SENSOR
OPTION 2 Step 2: CONNECT BOILERS IN DAISY CHAIN
2. Connect the boilers in a daisy chain, as shown below.
OMM-0145_D • GF-218 •
11/2/2020
MODBUS TRANSMITTER
Continued on next page
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