The Importance of the Probe in BACnet
When setting up 485 communication to a BACnet device like an AHU, it is important that you Probe it. This gets you some important information:
- Instance number is a good thing because if you add it to the program screen of the controller, it connects much faster when CBAS is restarted. Instance is usually provided in the Probe file but can sometimes have a different name.
- A Probe gets you the list of points that are on the AHU controller. Then you can add them from the Probe file easily by clicking the controller then click Add Points From Probe File.
- Perhaps the most important advantage to probing is that it automatically sets a few parameters to be used by CBAS that can improve performance. Note that you can alternatively set these parameters manually.if probing isn’t possible The most useful of these settings are are COV and Read Multiple. COV is Change of Value and if it is available, it sends any changes in value to the host. Read Multiple reads up to 14 points at a time. By default, CBAS only reads one point at a time unless you have Read Multiple set.
Continue reading George’s CBAS Tips, July 2018