Hello tulip;
Once you have selected the analog input module you will use and designed the circuit that will provide the voltage or current range that can be read by that analog input module (and this is your first issue, as was pointed out by Mr. Stone), the next steps are:
-Place it in the PLC rack (if it is not there yet); on some AI modules, capable of different voltage/current ranges, there are some square hardware dongles (on the side of the module) that must be adjusted for each channel, depending on the range you will use for your process. Details are provided in the docs accompanying the module, or the S7-300 Module Data manual (available from Siemens' website).
-In the HardwareConfig editor, select the correct module, insert it (drag & drop) in the correct slot; double-click on the module to open the properties page, and select the appropriate voltage/current range for each channels, the hardware interrupts if available...:
Notice the addresses given to you by the configurator (here, Inputs 256...271). This represents 16 bytes, or 8 words, one for each channel. Channel 1 will be read at address PIW256, channel 2 at address PIW258...
The numerical values that the program will recieve from each channel will be in a range 0-27648 for a valid reading (0-10 V, 4-20mA); anything below is a underflow error, anything over is an overflow. Again, this is explained in the manual cited above.
To scale the 0-27648 numerical value to engineering values of your choice, esaiest is the function FC105, "SCALE", that you will find in the Libraries tab of the Ladder editor, in the TI-S& blocks.
Hope this helps,
Daniel Chartier
