How to calculate the NTC ot Potenciometer as a thermal switch?

[Chriss]

Hi!
I have to make a simple circuit with UA741 OPAMP, NTC and a potentiometer for temperature monitoring.
I have an 2K2 NTC which would be connected to one gate and I have to put some potentiometer to the
other gate of the UA741.

With the potentiometer I should adjust the temp between 30-60C or something around.
So, here I need some help.
What value of the potentiometer should I use to have a larger step of temperature adjustment.
I mean, I won't does If I move the potentiometer 1mm left or right does the temp moves 30C etc.

I played around with several potentiometer but it went over my head and I have no usable info also... 

Any advice which value should I use of the potentiometer to have a nice path in temperature until I move the potmeter
would be great for me.

Thanks for any advice.
My best regards.

[mikerj]

When a potentiometer is driving a high input impedance (like an op-amp input) then the total resistance value of the potentiometer makes no difference to it's output voltage range. 

Vout = R2/(R1+R2) * Vin where R2 is the lower part of the resistance track in use, and R1 is the upper part.  You should be able to see that changing the total resistance value (R1+R2) will have no effect on the output voltage since the ratio stays exactly the same.

The way to restrict the output voltage range is by by adding fixed resistors in series with each end of the potentiometer track connections. e.g. if you had a 10k potentiometer and added 10k resistors either end of it, the voltage output range would be 1/3*Vin to 2/3*Vin.