Thermistor question

[RadioCrack]

Hi, I pretty much know nothing about thermistors and how to select them.
I need a thermistor that linearly increases resistance from 100k to 200k, when temperature linearly rises by 75C. Can you help me out?

 

[Sceadwian]

You will not find a thermistor that can do that. Thermistors are by nature non-linear, and can't be selected by resistance range like that. It would have to be an IC or otherwise active circuit that convereted a thermistors output linearly into an equivilant transistorized ouput resistance in the desired range.

 

[philba]

why the requirement for linear? maybe you should describe your application.

 

[gramo]

If your looking for an analogue device, perhaps the **broken link removed**will work for you?

It provides a 10mV/Degree output, and the scale depends on how it wired up.

Here's an example for a -55 to +150 degree temperature sensor (there are simpler ways to go about it, check the LM35DZ datasheet)
**broken link removed**

A great digital solution is the **broken link removed**
**broken link removed**

 

[RadioCrack]

I'm working on a pH probe amplifier and the mV output of a pH probe is dependant on temperature (and the concentration of H+ ions ofcourse). So I need some sort of temperature compensating device or circuit that'll decrease the gain of the probe's non-inverting amplifier as temperature increases and vise versa.

Some kind of LM35DZ circuit would be perfect; i better get cracking. Thanks gramo and everyone!

 

[ericgibbs]

G'Day Gramo,
Ref the Lm35, I did find when I did tests using +5V to the device, with two diodes to 0V, I had linearity problems near the high tempr end.

The spec sheet says Vop = 4 to 30V, with a +5Vs and Vdp of 1.4V with two diodes, the Vs across the LM35 is only +3.6V.

I had to increase the Vs, as I had a +9Vs on the board, used that and it cleared the problem.
EDIT: Look at the Datasheet Fig #7, the +5V is now +Vs!

Liked your movie, yesterday, re the stepper, nice one!, answered the OP's query.
Will buy you a film Directors chair at Xmas.

Regards

 

[gramo]

I had to increase the Vs, as I had a +9Vs on the board, used that and it cleared the problem.
EDIT: Look at the Datasheet Fig #7, the +5V is now +Vs!

Too true.. I never actually took it that high to find out!

Liked your movie, yesterday, re the stepper, nice one!, answered the OP's query.
Will buy you a film Directors chair at Xmas.

If a picture can tell a thousands words, then a movie with hundreds of frames must be a paperback novel!

 

[gramo]

I think I'll change my example to something like figure one (+2 too +150 Basic Centigrade Temperature Sensor) on my site

It would probably be a whole lot easier for people to understand, and I'll just suggest other applications by referring them too the datasheet