Obvius BACnet - Manual (Page 12)

BACnet Server for AcquiSuite Page 12 of 52
CVS:bacnet/Documentation/BACnet_Users_Guide.doc
Generally speaking, the performance bottleneck is the connection between the AcquiSuite and the
Modbus meters – either Modbus/485 or Modhopper wireless mesh network.
This means the best data-refresh interval or logging period can be estimated from the RS485 baud rate,
the meter’s response time, the amount of data being queried from the meter, and knowledge of how many
“Modbus transactions” are needed to query all the meter’s points.
(data_bytes_per_meter * 10 bits/Byte)
refresh_interval ≈ num_meters *
[
______________________________ + (meter_response_time * blocks_per_refresh)
]
RS485_baud_rate
Note: if the meter is connected via Modhopper(s), “meter_response_time” should include 500 ms per “hop”.
The following case studies give the results of this calculation for several common situations.
Please see Optimizing Polling and Optimizing Response Time for a full discussion of factors affecting
update rates.
The BACnet Server for AcquiSuite continually measures the average and worst-case response time of
each backend meter; these statistics are displayed on the BACnet à Device List à show: [stats] tab and
are useful for system performance tuning.