On Mar 2, 9:28*am, msg wrote:

I'm working up a demonstration of an antique electronic temperature
controller which needs a sensor with a PTC of about 5 to 6 ohms/degree F
average (at 20 degrees C); nickel-iron resistance wire fits the bill
fairly well, and I would like to find a coil on a low-mass substrate,
like ceramic, of roughly 1150 ohms at 20 degrees C

What alloy, exactly, of 'nickel-iron' do you have in wire form?
5.5 ohms/F at 1150 ohms is about 0.5% per F, 0.9% per C.
That's rather high (0.3% per C at room temperature is 'normal'
for pure metals like Cu). Usually, alloys have LOWER
temperature coefficient than pure metals.

Chrome-nickel (like 80% Ni/20% Cr, "Chromel A") heater
wire comes in at 0.007% per F.