you have many choices to look at, may I suggest the following.
0-10 volts, -10 to +10 volts, 5 volts, 4-20ma, 0-20 ma and others.
Design your plc system and allow for analog connections.
determine what signal feedback you need into the plc analog inputs.
see what you can find on the market that fits your needs.
if electrical interference may be an issue, use 4-20 ma for example.
look at your customers / application requirements, I always try to beat the specs by at lease 1 decimal point. if its +/- 0.1 units, I try to be accurate to +/- 0.01 units.
read up on the devices and see if they are compatible.
when you purchase your devices, you will need to program the analog inputs to your required scaled values based on the plc you are using.
hope this helps,
james