[SOLVED] Temperature measurement at: 120-165 °C

[saranaz]

you may use PTC or NTC thermistor it also works in this range. you may see this example

https://ibrahimlabs.blogspot.com/2013/07/temperature-sensor-using-thermistor-ptc.html

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you may use PTC or NTC thermistor it also works in this range. you may see this example

https://ibrahimlabs.blogspot.com/2013/07/temperature-sensor-using-thermistor-ptc.html

 

[FvM]

I found the relation that the voltage is changed as 1.4mV/°C. Depending on this I tried to calculate the voltage from the divider and then convert it to temperature dividing by 1.4mV. Unfortunately it shows data that is not accurate.

Pt100 is the industry standard solution for accurate measurements in the 0 to 400 °C range. It can be implemented as a simpled ratiometric measurement with a voltage divider, similar to post #19. But you can't achieve sufficient resolution and accuracy with a µC 10 bit ADC. You should have realized that the said 1.4 mV/°C (or a similar number) is only a fraction of the ADC LSB. Some options to get a better resolution:

- use an amplifier, e.g. x10
- use a higher resolution ADC
- use Pt1000 instead of Pt100

Reducing the reference resistor value isn't a solution because it would cause excessive self-heating of the Pt100 sensor. Only in some application with good thermal coupling, the sensor current might be exceptionally increased to 10 or even 20 mA.

In addition, the measurement with an µC internal ADC needs usually analog and software filtering to utilize the theoretical 10-Bit resolution. Slow ADCs, e.g. sigma-delta or dual-slope give need typically less filtering.

A disadvantage of the voltage divider circuit is the nonlinear characteristic of the R2/(R1+R2) function. It should be eliminated in software before the result is finally scaled. But it is worth doing because the overall accuracy depends only on Pt100 sensor, reference resistor and ADC, but no other components.

 

[Mithun_K_Das]

Thank you FvM for your very good suggestion. What I'm really want to do is your first suggestion. I want to use the voltage divider and an Op-Amp of X10 gain and then measuring it by ADC. But one problem is still remaining, the Rpt100/(R1+Rpt100) term. Its have a non-linearity nature. But I think it can be eliminated from the calculation.

Today I'll try this. Then lets see what happen.

 

[Mithun_K_Das]

Yes, Finally its working. What I did?

I used an Op-Amp Amplifier to amplify the voltage across the sensor, PT100 was feed by a CC source(5mA). And using a look-up table resistance is found and from that, calculating the temperature. I run the machine, and its running now....


Thanks all...
please visit: www.facebook.com/mlabsbd.

 

[abelt]

What sensor is better for measurement of temperature around 120-165 °C ? Will LM35 work at this high temperature?

Some NTC and RTC sensors work up to 300 degree centigrade. They are cheaper and do not need much signal conditioning for like taking ADC. ;-)They are resistors that vary resistance according to the temperature. However, it depends on the kind of uncertainty u can accept. I usually use them for temperatures like your measurement range. DO NOT USE LM35 FOR THIS TEMPERATURE.

 

[Mithun_K_Das]

Some NTC and RTC sensors work up to 300 degree centigrade. They are cheaper and do not need much signal conditioning for like taking ADC. ;-)They are resistors that vary resistance according to the temperature. However, it depends on the kind of uncertainty u can accept. I usually use them for temperatures like your measurement range. DO NOT USE LM35 FOR THIS TEMPERATURE.

You may not read all the post before you posted. Anyway thanks for your suggestion. The problem is solved now.