Obvius BACnet - Manual (Page 44)

BACnet Server for AcquiSuite Page 44 of 52
CVS:bacnet/Documentation/BACnet_Users_Guide.doc
3. 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.
Login as “admin”, navigate to Modbus à 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:
4. 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.
5. 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 BACnet
à
Device
List à show: [stats] tab , 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,
b. Optimize response time ,
c. Reduce the load on the RS485 bus by reducing polling rates 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.
6. 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