Specifications

MODBUS COMMUNICATION MANUAL
5-4
5.3.2 BMS Modbus Remote Setpoint Control By An EMS Master
To configure the BMS for Remote Setpoint Control from an EMS Master, proceed as follows:
1. Press the FIELD ADJ key on the BMS front panel to enter the Field Adjust Mode. The
yellow LED on the key should be lit.
2. Press the AIR TEMP key until RS232 MODE is shown on the top line of the display. If
necessary, press the ▲ or ▼ arrow key until MODBUS SLAVE appears in the second line of
the display.
3. Press the AIR TEMP key again until RS232 BAUDRATE is shown on the top line of the
display. Press the ▲ or ▼ arrow key to select the appropriate baud rate.
4. Press the AIR TEMP key again until MODBUS ADDRESS is shown on the top line of the
display. Press the ▲ and ▼ arrow keys to set the required address for the BMS on the
Modbus Network.
5. Press the AIR TEMP key again until NETWORK TIMEOUT is shown in the top line of the
display. Press the ▲ and ▼ arrow keys to select the maximum allowable time (in seconds)
for the EMS (or BAS) to refresh the Remote Setpoint information being sent to the BMS.
AERCO recommends that a time be selected that is at least 3 times the normal refresh rate.
This will allow for the loss of 1 or 2 transmissions without timing out.
6. Press the AIR TEMP key again until REMOTE SIGNAL is shown in the top line of the
display. Press the ▲ or ▼ arrow key to select MODBUS.
7. Press the FIELD ADJ key to exit the Field Adjust Mode. The yellow LED on the key should
go off.
8. To set the BMS for Remote Operation, press the CONFIG SYS key to enter the System
Configuration Mode. The red LED on the key will light.
9. Press the FIELD ADJ key until HDR SET MODE is shown in the top line of the display.
Press the ▲ and ▼ arrow keys to select REMOTE SET TEMP.
10. Press the CONFIG SYS key to exit the System Configuration Mode. The red LED on the
key will go off.
The BMS is now programmed for Remote Setpoint Operation from an EMS Master. In the
event of a Modbus signal interruption, AERCO recommends that the TEMP FAIL MODE setting
be set to Switch Inputs if you want the BMS to continue running the Boilers in the CONSTANT
SET TEMP Mode. In this case, ensure that the REF TEMP is set to the desired setpoint
temperature.