Obvius BACnet - Manual (Page 13)

BACnet Server for AcquiSuite Page 13 of 52
CVS:bacnet/Documentation/BACnet_Users_Guide.doc
2.2.1 Case Study: Meters Connected via RS485 at 9600 Baud
The table below shows the best data refresh interval (in seconds) you can expect using Modbus/485 at
9600 baud for a variety of common meters.
The green region are the configurations recommended by Obvius.
The gray (middle) region is only relevant if you are attempting to control Modbus relays as well as reading
meters. This region is where the Modbus/485 response time has exceeded the default BACnet
APDU_Timeout of 6 seconds (minus 1). As a result, any attempt to write a relay will time-out. Increasing
the APDU_Timeout will “solve” this problem, though at the expense of making any control-loops less
responsive and more difficult to debug.
The red region is where the delay has become so great that the BACnet Server will always report the
meter as being in a failure state.