Need to know of any transmitters out there that can take a 0volt to 8volt non-linear signal and convert it to a linear 4ma to 20ma signal or 0volt to 10volt linear signal.
Have a look at this instrument. It might be what you need.
Dan Karppi CCST III
That would be a most interesting device for
an arbitrary non-linear signal. A PIC or
similar with an ADC a lookup table and a DAC
would probably be the closest practical thing.
This is exactly what a thermocouple transmitter does. If you have a plot, a transmitter company should be able to make one for you.
This cannot be answer without knowing what kind of non-linear signal you have. There are, for example, converters for the squareroot function, which occurs e.g. in flow measurement.
There are converters for the non-linear signals of every kind of thermocouples.
If your signal has some very weird non-linear chracteristic, there is allways the possibility to read it in to some analog input of a PLC, program a conversion table and deliver the result from a table lookup to an analog output.