> Why not just measure the temperature of the resistor and compensate
> for any induced resistance change?

Needs to be as cheap as possible.
No processor involved.
Analog compensation possible but annoying and adds components.

> ... Or do you need the instantaneous resistance to be invariant?

Essentially yes.

> What about using PCB traces as resistors? Air cooled if necessary?

Could be OK if temperature variation can be guaranteed to be kept low.
Copper links would serve as well.
Limiting temperature variations with loading a potential hassle.

> As for 'adjusting', why not use standard low ohm resistances and
> series/parallel them as needed to come with a 'custom' value. 
> 1,2,4,8 sequence
> is easy to use in series configurations.

As per my prior comment

>> - Suitable wattage, temperature invariant sub 1 ohm resistors tend 
>> to
>> be specialist and expensive compared to other costs in this
>> application.



        Russell


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