NTC temperature reading

NETMF & Gadgeteer
1

Hi all,

i am having some troubles with converting a NTC value to a temperature.

The ntc is connected to one of the analog inputs of our emx module. There is a resitor in serie with it of 10K. The ntc also is a 10K type. So this means that it’s resistance is 10K at 25 degrees (celcius). We are measuring between the resistor and the ntc, so at 25 degrees the voltage will be devided in half (half of the supply voltage, which is 3,3v).

Now i am measuring 1,325v. I can calculatie the milli amps that is running through the 10K resitor. With that i can calculate the resistance of the ntc at that moment and that should 7,7K ohms.

But now i need to convert this to a real temperature. All the normal formulas require Log() functions, which the .net micro framework standard doesn’t have. I have tried elzes math libary, but i can’t seem to get it to work…

Anybody that has worked with temperatures in this way before with .net micro? So NTC, or PT1000 & PT100?

Regards,

Per

2

Go here
http://www.ghielectronics.com/downloads/NETMF/Library%20Documentation/Index.html

Find GHIElectronics.NETMF.System Namespace and then MathEx class :slight_smile:

3

I’m also interested if anyone has any experience with those sensors. My friend asked me to do a solar water heating system monitor and I want to use a FEZ for that. Right now all I know is that the system using this controller:

http://www.solar-water.co.za/downloads/SR868C8%20Manual.pdf

that has both kind of sensors connected:

NTC10K
PT1000

I don’t know yet how to split the sensors so that they can be read by both, the controller and FEZ, but i will ask about that in a separate thread.