Multiple 4-wire PT100s with same excitation current?
In a perfect setup, no.

The thing I'd be aware of is, that you have different absolute voltages for each of your PT100, which might be an issue for your sense circuit:







simulate this circuit &ndash; Schematic created using CircuitLab

You have 100 mV over each PT100, but for sensing the voltage across R1, you have a 300 mV offset (in this case).

It shouldn't be much of an issue, but depending on the voltages you work with, it might get out of range.

You must use the each pair of sense wires to keep the accuracy, although in the schematic two sense wires will effectively be at the same node (the one between R1 and R2 for example), in real life they will not have the same voltage (because there is another piece of wire between them).

One thing which might affect accuracy is the input current into each of the sense wires: each resistor will get less and less current, so you don't know how much current is actually going through each resistor. But with a good sense circuit this effect should become rather small.

With the AD7195 you should be fine as long as you don't exceed the maximum input voltage on the input (AVdd). I haven't seen any mention in the datasheet which would limit the common mode voltage. Input current in buffered mode is in the order of 5 nA, so you might wanna check if a missing current of 5 nA is a problem for you. If you are not using buffered mode, the input current is in the order of some µA, so it gets more noticeable.