NTC thermistor Temp sensor

[Derrihj]

Atleast 500 degrees C should be the max of the sensor

[medelec35]

Thermisors can't measure temperature that high.
A RTD will be more suitable.
Since slope will be about 0.385R/C (depending the the RTD used) then an amplifier will be required.

[Derrihj]

Thanks for that info, now interfacing the RTD do you have a flowchat for RTD or is it smilar to that of the thermistor?

[medelec35]

No, the calculations will be different as slope will be linear, instead of logarithmic.
should be easier to calculate.

[Derrihj]

Ok I will look into it and if things put up a angry face on me i run back to you for help. But do you have a link for a good RTD in that temp range nice mounting for oven with a nice DataSheet that i can order?

[chad]

Hi Martin,

Yes I did! And after some initial testing it matches room temperature and an ice cube very closely. Looks like I lucked out with the NTC.
I also learned that a .in front of a variable is local to that macro? And also that you can just reuse it. I'm Still a noob.

Works Great!


Thanks!

Chad

[Derrihj]

Ok, i dont know how the thermistor component works but i really need to know how it works coz imagine i don't have the beta coefficient value and the only option is to use the thermistor component, i have tried it and am not getting good results.Temp value not changing with changing temp stuck on -20°C on real board but in my flowchat it does change, Reason is am not doing things the right way with the thermistor component.

[medelec35]

Yes I did! And after some initial testing it matches room temperature and an ice cube very closely.

That's great thanks for letting me know

I also learned that a .in front of a variable is local to that macro? And also that you can just reuse it. I'm Still a noob.

That's correct.We have all been there.
The fun is the learning part and have a working project at the end.

Temp value not changing with changing temp stuck on -20°C on real board

Just tried your flowchart and hardware is working ok with thermistor component.
Did not need to modify to get it to work.

Does the resistance value change and what is it showing for room temperature?

[Derrihj]

On my board room temp it shows 16k and resistance value is changing ( reduces when i press my fingers) but not the temperature (stuck on -25°C)

[Derrihj]

But i think also my R2 calculation is not right please look closely on it in my flowchat and see if its right

[medelec35]

Temp value not changing with changing temp stuck on -20°C on real board but in my flowchat it does change

It's because you have the wrong ADC channel selected within thermistor component properties.
It does not match the POT ADC pin connection.
You need to ensure both match.

[medelec35]

On my board room temp it shows 16k

That's not 16k that's 160k which will be wrong.
Looks like an hardware issue.
On my hardware using your code, the resistance is showing approximately 9k and temperature of approximately 36C
It's out to my room temperature as you have entered 12490 for 25C which should represent the actual thermistor resistance.
Mine is 10k

[Derrihj]

I don't get it ,did i post a different flowchat coz here i have it on An3 for both.

[medelec35]

Have you measured the voltage on pin AN3 with respect to GND?
If so what is it?

[Derrihj]

I can see 4 volts there

[medelec35]

I can see 4 volts there

What temperature are you expecting?
That does not make sence.
If VDD is around 5V and you have about 4V on the ADC pin then you should be seeing around 2C and 28k
If seeing -25 then does not look like correct pin with the 4V on it is being read.
Also if not expecting 2C then hardware is wrong as the voltage is not correct.

[Derrihj]

Ok 4 volts at the adc didn't make sensor to me even when i removed the NTC so i looked closely to the PCB since this PCB was not not for a temp project i just made loops on it some how one root got into contact with the 12v supply messing up all readings fixed that and everything seems ok now thanks Medelec35 for you being really patient with my mistakes.

[medelec35]

It's Ok Derrihj,
The main thing is we got to the bottom of the situation and it was resolved.
So you have a 12K thermistor?
If supposed to be 10k, I would take more samples of Temperature V resistance.
As said previously, the resistance at 25C is the actual themitor resistance.
So if 10k thermistor used, at 25C the resistance will be 10k.

[Derrihj]

Oh you don't know how much i like you Medelec35 you are really a problem solver now that is out of the way the remaining part is my mother's cake cooker since u told me RTD is the way to go,we have to look at that too,coz I've already finished the code for ther timer and it works greate i now only need calculations for the RTD

[medelec35]

Thank you Derrihj,
kind words that are appreciated.
I have added extra text to my previous post for you to read.

i now only need calculations for the RTD

That can only be completed after the RTD is chosen hardware has been designed.
The ideal would be to set amplifier so you get a change of say .1 C change for every 5/1024 = 4.88mV
I have no experience with RTD, but that is how I would do it.
If does not have to be too accurate then I would probably use the 2 wire RTD.
I'm sure there are members on here who have more experience with RTD's and can better guide you?

[Derrihj]

Ok i will do some research on the RTD first and see the best way to go then the rest of the members will come in and help.

[Derrihj]

Got another 10k Thermister and works really nice "right on the money" with your Beta version Medelec35.

[Derrihj]

I moved the RTD research to a new topic ( RTD temperature Reading) which in my thinking was that it will be easy for people out there searching for RTD knowledge in flowcode rather than it being hiden in a different topic which is the NTC thermistor.

[medelec35]

Glad the beta version works.
Thanks for letting me know.
Good call with RTD moving to a new topic.

[Derrihj]

Yes Medelec35 i thought using the Steinhart and Hart equation was the best way to go with more accuracy but am having second thoughts, your Beta version is right on the money just like " an angry female lion with cubs to feed"