331-7kf02-0ab0 with pt100

Dear Experts,

i am using AI 8x12 Bit Analog input module (MLFB: 6ES7 331-7KF02-0AB0). at its input channel i have connected a 4-wire RTD PT100 with climatic range -50 C to 100 C. now my questions are

1) if i remove the M+ and M- wires from PLC side it shows 100 C at HMI, but if i remove Ic+ and Ic- it shows a 0 C. how this logic does work??? why it is displaying a different reading???

2) what is the meaning of 12 bit or 16 bit which is written on the top of the AI or AO module??

for ex. AI 8x12bit. 

please explain in detail.

Hi Jignesh

I Suggest to have a look in this Manual https://support.industry.siemens.com/cs/us/en/view/8859629

In Chapter 5 there is a detailed description on the Analog processing

In short, Analog Value in Siemens goes from 0 - 27648 ie. 4 mA = 0, 20mA = 27648. This is the same nomatter the Resolution. The differene is how fine step you take.  See the Attached image to see the Steps regarding different Resolutions

BR. Sven