Issue
The BACnet object goes into fault when writing a NaN to an MNB controller.
Product Line
TAC IA Series
Environment
- I/A Series MNB VAV
- I/A Series MNB 70
- I/A Series MNB 300
Cause
Firmware 1.424 and higher responds to receiving a NaN with an Error: "value out of range". In firmware 1.420 it would accept the NaN and respond with a normal acknowledge message. This is a result of a change required for BTL compliance.
Resolution
A slight setup change can accomplish the same result without causing the object to go into fault. In the ENC edit the properties of the AVSPP object and set the fallback to "null". Go to the slot sheet of the object being overridden to hide the "Set" option. This will prevent the operator from attempting to send a NaN that causes the fault. When a right-click override is performed only the emergency (priority1) and Override (priority8) choices are displayed. When the override expires or the object is manually put back into “auto” the “fallback” value is output which is “null” and that is accepted at the controller and serves the same function as sending a NaN.
