how to diagnosis an open loop in 810 AI analog input modules instead of reading lower signal range (i.e 4 mA)
Notice that CBM offer libraries for AI handling e.g. Signallib with e.g. the SignalInReal.
In general the Underflow and overflow is indicated by system alarms when enabled in hardware configuration by setting “System alarms on hardware units”, this function is by default enabled.
So dependent on what you want to achieve.... good luck :)