Download BACnet Spyder Tips

BACnet Spyder Tips
The following were tips taken from John Hutchey’s BACnet Spyder Class
BACnet Spyder Hardware and POWER wiring
1. Spyder TRIAC outputs are rated at .5 amps continuous and only .8 amps inrush. They work fine pulling in relays, but
larger contactors that may be found on compressors, pumps and fans may cause the Triacs to fail by sending a back
surge of voltage through the energizing coil when the contacts close and the magnetic field collapses. One solution is to
drive pilot relays with the TRIACs that can be used to pull in larger contactors, the other is try using MOV surge
suppressors or transorbs across the outputs. The MOV/Transorb devices are typically much less expensive then adding
relays. Transorbs respond quicker and clamp harder than MOVs.
2. With RS485 bus communication, grounding is critical. The common 24vac must be tied to earth ground. This can be
done at the transformer or at the Spyder.
3. If using a single transformer to power multiple Spyders, be sure to ground the transformer at only ONE spot and NOT
at every BACnet Spyder (this is different than LON where every Spyder is grounded regardless of how many Spyders are
on a transformer).
4. Proper wire type, termination resistors and proper bus biasing is CRITICAL for reliable network communication. Proper
shielding and grounding is also required. Use a dual-trace oscilloscope to assure that the bus is noise-free, that the signal
strength for the combined A-B channel is at least 2 volts, that the bus is properly DC biased, and that the waveforms are
square without excessive saw-tooth or ringing.
- Note, typically only ONE device on the BACnet RS485 bus is used to provide the bias voltage...
5. If using the standard RS485 port on a JACE 200/600 series, biasing is NOT enabled by default. To bias the bus, add a
small jumper onto the main board. This requires disassembly of the JACE. The jumpers may be special-ordered from
Radio Shack. The are called DIP Shunt Shorting Jumpers - part number 276-1512 in packs of 10. You'll need 2 jumpers on
the main board, adding them vertically across the pins by the COM port (one across the two left pins, one across the two
right pins).
6. If using the add-on RS485 option board, the two ports including BIASing jumpers - these can be enabled to bias either
or both ports.
See the installation instructions on the option board for details.
NETWORK configuration / Spyder Network points
1. A RS485 bus can support up to 32 full load devices. The BACnet Spyder is a 1/4 load device. Routers and the JACE
count as a full load device. When in doubt, count any device installed on the BACnet RS485 bus as a full load and don't
exceed 32 full loads on a single RS485 trunk.
2. If using BACnet IP routers, be aware that by default, the discover function may not work though LANs and WANs. If
the JACE and the routers are set up with BBMD mode enabled, then you may be able to discover them, but by default,
BBMD is not enabled.
3. A quick tip on tuning the BACnet MSTP network is to configure the max info frames property to max value (100) - this
will let the BACnet bus maximize the size of a packet to move data quickly.
4. Adjust the default (normal) poll rate on the BACnet MSTP port to assure that the bus isn't being overloaded. NOTE,
since BACnet uses 2 simultaneous threads for communication, the maximum busy time suggested is 120% (not the usual
60% on all other networks).
Spyder Network Points
1. Unlike LON, BACnet Physical Points automatically create BACnet objects that can be dropped into the point folder as
proxy points, no need to create NVOs - BUT be sure to NAME the physical points WHEN YOU ADD THEM TO THE SPYDER
and not using the re-name feature, so that the network point that is automatically created gets the proper name (and
not just something generic like NetworkOutput).
2. Unlike LON, BACnet Physical outputs points may be directly over-ridden from the proxy point and will override at the
same priority level as the WEBs proxy point.
3. Keep in mind that the default internal update time for datapoints from a BACnet network to update the internal
network points in a Spyder is 15 seconds. This can be changed by going to the advance setting on the NetworkInput
objects inside the Spyder, so plan your Spyder code accordingly.
4. By default, the Spyder NetworkOutput points have guaranteed periodic refresh (GPU) turned ON and is set for 60
seconds. Change the default value if needed under the point's advanced settings.
5. By default, Spyder NetworkInput points have fail detect enabled, and set to 60 seconds. The Spyder fail detect
algorithm requires five failed messages in a row before a NetworkInput point shows failure (300 seconds / 5 mins) and is
appropriate for linking from a point with a 60 second GPU (see note 4 above).
6. Unlike LON, WEBs station BACnet proxy points writing to devices do NOT automatically have a guaranteed periodic
refresh rate. By default, BACnet proxy points only write onto the network from a WEBs station when the value changes.
This will lead to NetworkInput points failing after five minutes if the point is static from the WEBs station (see note 5
above). In order to configure a WEBs station to re-write on a BACnet bus, duplicate the default tuning policy (name it
something like ReWrite) and set the max write time from 0 (no re-write) to 60 seconds. Then, for every proxy point in a
WEBs station that is associated with a BACnet NetworkInput, change the tuning policy for those specific points from the
default to ReWrite. This will force the WEBs station to re-write those BACnet points every 60 seconds and will avoid
point fails in BACnet Spyder NetworkInput points. --- do NOT use the new tuning policy to rewrite to NetworkSetpoint
objects in the Spyder, as constant re-writes will damage the on-board flash memory chips when writing to setpoints.
Do this ONLY for NetworkInputs!
7 Note: Unlike LON NCIs, in BACnet, NetworkSetpoint objects get polled and automatically updated in the WEBs
database, so there's no need to use a special polling folder or any other mechanism to assure that Setpoints read
correctly in a WEBs database if they are changed from a ZIO or other device.
8. To automatically sync up the clocks on BACnet Spyders, drop in the timsync object from the Venom palette onto the
network and configure the sync properties.