When selected, the Idle Bus Menu reads the bus bias voltage when no communications are present. Proper idle bus voltage levels will not be displayed unless EOL termination is present. The idle bus voltage menu shows the + line voltage with respect to the COM line and the – line voltage with respect to the COM line. The FIT can still read this voltage on an active communication bus by taking readings during communication pauses. For acceptable Idle Bus Voltage ranges, see Voltage Levels and the Voltage Table .
Note: It is possible and normal for there to be minor voltage fluctuations while reading Idle Bus Voltages.
Figure 1. Idle Bus Menu
See Idle Bus Voltage Levels for more information.