Dear Sam_ron
have a look at the the three Getting Started Guides below, they should contain all the answers for AI's that you are seeking:
SIMATIC S7-300 SM331; AI 8x12 Bit Getting Started part 1: 4 -20mA
https://support.automation.siemens.com/WW/llisapi.dll?func=cslib.csinfo&lang=en&objid=17473828&caller=view
SIMATIC S7-300 SM331;AI 8x12 Bit Getting Started Part 2: Voltage and PT100
https://support.automation.siemens.com/WW/llisapi.dll?func=cslib.csinfo&lang=en&objid=18971030&caller=view
SIMATIC S7-300 SM331; AI 8 x 12 Bit Getting Started part 3: Thermocouples
https://support.automation.siemens.com/WW/llisapi.dll?func=cslib.csinfo&lang=en&objid=18972936&caller=view