Obvius BACnet User Manual

Page 44

BACnet Server for AcquiSuite

Page 44 of 52

CVS:bacnet/Documentation/BACnet_Users_Guide.doc

Meter communication errors (at Modbus level)? To verify that the AcquiSuite itself can

successfully set or clear the relay, try changing the relay’s state from the AcquiSuite’s web UI.

Device List, and click on the relay device. You should

see a list of points. Locate the relay, and you should see buttons to turn it on or off, like so:

APDU Timeout too low? It possible, though unlikely, that the APDU Timeout is high enough to

allow reads to succeed, but not writes. BACnet reads are satisfied very quickly from cache, while

writes to relays always result in a Modbus write to the relay. This write must finish before the

BACnet Server will reply with success. Assuming you’ve already verified the Modbus timeout is

sufficient to write to the relay (above), try doubling the APDU Timeout.

AcquiSuite’s RS485 bus is overloaded? Each BACnet write to a relay’s Present_Value will

result in a Modbus/485 request on the AcquiSuite’s RS485 port. If the RS485 port is simply

overloaded (all bandwidth in use), requests will be delayed, and if this delay is great enough, it

will exceed the BACnet Server’s APDU Timeout. To diagnose this, navigate to

, and look at the “I/O Response Time, Worst-case” column (indicated by

arrow).

This value should always be less than the APDU Timeout. If this is the problem, several solutions

are possible:

a. Increase the APDU Timeout,

c. Reduce the load on the RS485 bus by

or reducing the AcquiSuite’s

Data logging period,

d. Increase the RS485 bus bandwidth by reconfiguring your meters to operate at a higher

baud rate.

Your Controller may require writing be enabled in software. For instance, the Tridium JACE

Controller, when adding a Binary Value point, assumes it is read-only. You must specifically tell