There are two parts to configuring a Siemens S7-300 analog input. There's the software part carried out in the Hardware Configuration (yeah, having just re-read that it does sound a bit strange - you do the Hardware Configuration using software. Oh well, whatever). This tells the CPU the signal type, range, etc which will be returned by the module.
However because all the circuitry for current, voltage, bipolar, unipolar, RTD, thermcouple, etc is already on board the one input card, how does the electricity know which way to go? The key here is a small plug which is inserted in the side of the module in one of four possible orientations. It connects or disconnects certain parts of the on-board circuitry according to the signal type. The software tells you which orientation to use for your chosen signal.
As far as I know all the modules I've seen get shipped with the plug in the position for 0-10V DC. This is presumably the safest setting as other incorrect wiring connections won't 'damage' this. However, if you've got it set for, say, the mV ranges of a thermocouple, and connect a 0-10V source to it, look out for the SEDs (smoke-emitting diodes) coming on. I think all voltage signals use the same orientation so you could in theory leave the plug in place and then select for 0-10V, 0-5V, 2-10V, 1-5V etc. But you'd have to change it (the plug) for current signals.
In summary, you can't change the signal type across the whole range of possibilities without attending to this physical aspect. And for this you need to remove the module from the rack. Whether, as indicated earlier you can really use an SFC to re-parameterize the modules at runtime is something I'll leave to others.
Ken
