This is a screen shot showing the on-line debugger running in i-TRiLOGI Version 6.6 build 04. The PLC is a Nano-10.
ADC(1) and ADC(2) are being accessed, periodically, as part of the PLC program. The ADC inputs are about 3.71 and 4.07 VDC relative to the analog ground reference.
Note the non-zero values for ADC 1 and 2 on the screen shot.
I suggest that you disconnect anything that you may have connected connected to your PLC (ADC) inputs. Now jumper the +5V analog reference voltage to one of the ADC inputs. This is the reference voltage used by the PLC ADCs and this voltage should result in the ADC measuring the full scale value of 4095 counts.
As noted by TRI support the PLC must be executing a PLC program that periodically "reads" the ADC values. Otherwise, the registers accessed by the on-line debugger will return a value of zero.
Another reason that you may get a zero reading is that voltage measurement is relative to the AGND input. If you try to measure the voltage of a D cell battery, connecting only the + end of the battery to ADC 1 will get you a zero reading. You must connect the - end of the D cell to the AGND, also.
Gary D