I have to select NTC for below temperature range :

Temperature range: -5°C until +35°C
Accuracy: ± 1%

So could anybody guide me how to select NTC and what could be NTC resistance value and accuracy.
I want to interface this circuit to microcontroller to read the temperature.
What could be design circuit and design calculation for it.

Thanks in Advance !!!

Regards,

 

hi 87,
Are you considering a NTC Thermistor.?
E

 

hi 87,
Are you considering a NTC Thermistor.?
E

Yes, NTC Thermistor.
Application is to measure the water temperature.

 

Application is water temperature measurement as per above range and accuracy but I am not pretty sure which devices is suited for this application

 

hi,
You can get glass enclosed NTC thermistors, suitable for immersing in a water surface.
As you may know their response is not linear.
E

 

hi,
You can get glass enclosed NTC thermistors, suitable for immersing in a water surface.
As you may know their response is not linear.
E

Could you suggest the part number and schematic for the same.

 

Is this a school/college assignment?

 

Is this a school/college assignment?

No, its practical application not assignment.
You can assume it freezer which is having option for hot and cold water.

 

Could you suggest the part number and schematic for the same

Hi,
Don't you have a draft design in mind.? that you could post.
E

 

Hello,

Here is an application note for thermistor to adc application.

Bertus

 

Hi,
Don't you have a draft design in mind.? that you could post.
E

No I do not have any draft design. I think , we can interface with MCU as per below.
NTC selection is critical for me for above specification

 

hi 87,
Are you going to program a MCU to correct/adjust for the non linearity of Temp versus Resistance.?
We need to know more detail about the project.
E

 

hi 87,
Are you going to program a MCU to correct/adjust for the non linearity of Temp versus Resistance.?
We need to know more detail about the project.
E

Our intention is only to read ADC value and based on that software will calculate the temperature.

I do know how to tackle non linearity of temperature sensor

Pl guide me to design temperature sensor.

 

https://forum.allaboutcircuits.com/threads/precision-thermistors.64095/

Temperature range: -5°C until +35°C
Accuracy: ± 1%

1% of what?

 

https://forum.allaboutcircuits.com/threads/precision-thermistors.64095/



1% of what?

1% is accuracy of measurement.

 

1% is accuracy of measurement.

That's just repeating what you've already said and does not answer the question.
You are parroting something you've heard without understanding what it means.
1% accuracy has to be 1% of some value.
For example it could be 1% of the temperature range.

 

That's just repeating what you've already said and does not answer the question.
You are parroting something you've heard without understanding what it means.
1% accuracy has to be 1% of some value.
For example it could be 1% of the temperature range.

Yes,Mr crutschow you are correct.

1% of temperature.

I do not have much idea about NTC and its practical implementation that is why I posted in the forum to get some idea of component selection and design. I am beginner not expert.

Probably expert people do not post such questions. So pl consider me a novice and give your inputs so that I will be able to select NTC and implement it.

Thanks !!!

 

The choice of NTC thermistor isn't critical if you are prepared to calibrate your system at two or three known temperatures.
Check the datasheet of a sample thermistor to get a feel for its temperature/resistance characteristic. From that you can decide on the value of R0 needed in your post #11 circuit.

 

The choice of NTC thermistor isn't critical if you are prepared to calibrate your system at two or three known temperatures.
Check the datasheet of a sample thermistor to get a feel for its temperature/resistance characteristic. From that you can decide on the value of R0 needed in your post #11 circuit.

Thank you so much for your reply actually that is what I wanted to understand.
Now I have two more questions to be answered:
1. How to select NTC for water application over temperature range of -5degC to 35degC for 1% temperature measurement accuracy. i.e. what could NTC resistance, NTC type, what all parameters need to be taken into consideration.

2. Which is appropriate circuit to linearize NTC over a temperature of above.

Answer of these two questions will give me clear perception to me and I will be selection and design NTC circuit.




Thanks in Advance !!!

 

Generally you want a thermistor that has about 1kΩ to 10kΩ resistance at the center of your temperature range.
Pick one that is rated for 1% accuracy of value over the range.

If you connect the thermistor in the feedback circuit of an op amp in a quasi-bridge connection which maintains a constant current through the thermistor, then the output voltage is a linear function of the thermistor resistance.
The LTspice of such a circuit is shown below for a typical thermistor:

The values shown give an output of zero volts at 20°C.
For your circuit you would likely want zero output at -5°C.

The gain is a function of the bridge reference voltage, Vb, which should be a stable voltage from a reference circuit, such as a TL431.

If you need more gain to match the micros input scale, than add a non-inverting op amp with gain at the bridge output.