Thermistor value ?K

What value thermister should I use (1k 4.7k, 10k, 47k, or 100k)?
The manual only shows the value of the 100K resistor.

Would a 4.7K thermistor and a 4.7K resistor be ok for simple temperature reading?

Thanks

They should be fine - you'll need to change the value of the resistor in the potential divider.

Generally the higher the resistance, the lower the power consumption.

A

Depends on what temperature range you want to measure and at what resolution.

This should give you a fairly useful range: Choose a divider resistor approx Rlow*4. Where Rlow is the lowest anticipated resistance of the thermistor. (Highest anticipated temperature)

So, if (say) your thermistor has an Rlow of 1k at max anticipated temperature, use a 4k balance resistor.

Using this rule, with the thermistor connected to +5v, the balance resistor to 0v and the junction of the two connected to ADC, you should read about 4v at max temperature.

When the temperature is nominal (25c), and the thermistor resistance is about Rlow*5, you’ll read about 2.2v.

Whilst it is app dependent, don't go too low... self-heating.

From your list of possible thermistor values, 10K would be a good compromise between self heating and meeting the input impedance requirements of the PICAXE. To minimize errors the series resistance seen by the ADC should not exceed 10K. If you use a matching value for the potential divider resistor, the equivalent impedance seen by the ADC will only be 5K.

Thanks for your input guys.
Extra thanks to boris, for the maths.

Given, that I don't know the changing properties of the thermisters,
I'll use a 4.7K thermister with ~20K resistor for testing temperatures below 25 degrees c.
and
a 10k thermister with ~40K resistor for testing temperatures above 25 degrees c.


Screech.

Sorry if this post might be seen as offtopic.
But wile we are talking about thermistor's I tought I would ask how you go about reading thermistor datasheets.

I am intrested in thermistor from rs, part number is 528-8536, and here is the datasheet

95% of the info shown in the datasheet means nothing to me

I want to make a Temp vs Resistance chart for this thermistor, so that I can make a lookup table for my picaxe projects.

Thermistor vs Temp is non-linear.

Why not search on the Internet?
Better descriptions and pictures are shown there than we can post here.
Here are a couple of useful links.

http://www.capgo.com/Resources/Temperature/Thermistor/Thermistor.html
(includes a calculator for thie products).
Note the self-heat value.

http://en.wikipedia.org/wiki/Thermistor
for general stuff

... and then have a look at Steinhart-fart.

Or,if that does your head in then buy one and do your own calcs.
If you were cunning you'd do a function in a spreatsheet or VB so you could measure a few points and calculate the rest and produce a table.

Or take some measurements, then use EUREQA to work out an equation for you. No table required

Good luck with the Maths programming
How do I ... etc.?