PTC (positive Thermo coefficient) device temp ratings.

One kind of PTC is essentially a thermal switch that changes from a low resistance state (that varies very little over a wide range of temperatures) below the switching temperature to a very much higher resistance, above the switching temperature. They are intended to either detect which side of a single temperature they are on (or provide a very sensitive temperature measurement over a narrow range of temperatures), or are intended to act as self resetting fuses.

Those intended as fuses are specified in terms of their switch off time versus current and temperature:

Those intended as temperature detectors are specified with a curve of resistance versus temperature, and usually a switching temperature (the temperature at the steepest point on the resistance curve).

The tires on my car are supposed to be inflated to 28psi when cold, but the colder I make them, the more air I have to put in. No doubt immersing them in liquid nitrogen would get them really cold, but I'm a little short on the liquid form right now, and don't have enough to dip a car tire in. I suppose I could extrapolate, but I figure inflating my tires to 60psi should be enough, even when the outside temperature reaches 150K (-190F). That won't help if I drive down a street covered with liquid helium, but what the hell - sometimes, you just have to throw caution to the wind.

-- Mike --

I've only collided with NTC's occasionally, do a search for siemens matushita B57164 data sheet, gives a lot of numbers, in centigrade, they seem to be referenced to 25C

martin

Now, there's a concept. The tire bomb. Just drop the tire in a tub of LN2, and fill it up with air - hey, wait a minute, won't the O2 condense out at LN2 temps? Hmmm... Anyway, set it where you want the explosion to be, and walk away. The nitrogen boils off, the air in the tire expands, and, BLOOEY! ;-p

They refer to 25 DegC, there should be an online translator to be found on the internet, I guess.

Rene