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

[Mithun_K_Das]

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

 

[paulfjujo]

hello,

you need to use PT1000 (easier as PT100)
or themocouple type K.
and an amplifier..to get a voltage ouput of 0.. 5v
or 4-20mA on R=250 ohms

 

[nitishn5]

The LM35 has a specification up to 150°C. And if you take a look at the curves in the datasheet, it shows graceful degradation beyond 150°.

I think you should be OK.

 

[tpetar]

Use thermocouple.


**broken link removed**


Tables of Thermoelectric Voltages for All Thermocouple Types
http://www.ni.com/white-paper/4231/en/
http://www.omega.com/temperature/Z/pdf/z204-206.pdf


Also all depends what you measure and how long. LM35 case will melt in some situations of direct contact, but will survive air temp measurement.



Best regards,
Peter

;-)

 

[Mithun_K_Das]

Thanks all, I'm checking the local market. Then I will inform you all again....

 

[jayanth.devarayanadurga]

Use PT100. It can measure upto 800 deg C.

 

[Mithun_K_Das]

can you give me the calculation of PT100?

 

[jayanth.devarayanadurga]

https://www.edaboard.com/threads/252959/

 

[Mithun_K_Das]

Not negative. I need to measure 100-165 degree C.

 

[jayanth.devarayanadurga]

You can modify the code. Just remove the calculation used for negative temperatures.

 

[Mithun_K_Das]

I'm using LM35. Lets see what happen. Hopping a good result.

 

[jayanth.devarayanadurga]

LM35 range is -55 to +150 deg C. You can't use it.

 

[Mithun_K_Das]

I know. But I talked with the user. They says they will use around 100-125 C. But they want the capacity up to 150 degree C. I think it should work.

 

[Mithun_K_Das]

Having trouble with LM35. Its has melted!!! I think I've to use PT100. But the link you posted is not clear for calculation. I also trying from this: https://www.picotech.com/applications/pt100.html.

But I'm confused about how to measure. Its just a tiny change in resistance there. Should I use any Op-Amp to multiply by 10?

 

[paulfjujo]

hello,

yes you have to use constant current generator or a bridge to use Pt100.
You can also use PT1000 ( 10 times PT100) to avoid problem (less problem) wuth the length of cable.

View attachment Pt100_docu.pdf
you can see Instrumentation AOP or normal AOP to use Pt100 (Pt1000) in a bridge.
There is also some industrial converter to convert Pt100 to 4-20mA ..into R=250 gives 1-5V (cost is less than 80€ .. xx$)

what accuracy do you need ?
if not so critical you can use this example (schematic) with a classic Ampli OP ( used for hetaer control)
and adapt the range .

 

[jayanth.devarayanadurga]

Woo hoo. That is the formula for +ve temperatures. :grin:

Tell me the range of temp you are measuring. I will write the code. Post your project files.

 

[Mithun_K_Das]

I was fool. Tried to measure the temp using just voltage divider like: This. Just replacing the thermistor by PT100. But when the wrong data comes out I was confused. Still now I'm trying to do that calculation like a fool. But I'm looking for a simple solution...

 

[paulfjujo]

tell us what is the range of measurement ?
what accuracy do you need ?
so, maybe you can use a simple solution : a quasi-linear response formula type y =ax+b easy to code in C
Delta is less than 2% in the range 0 to 180°C

or more precise :with a polynome formula.

don't forget, Pt100 itself has a accuracy domain.. depending of the class A, B or C
model A for the best accuracy, but also more expensive cost.
also, what length of cable beetween sensor and electronic conditionner input ?

 

[Mithun_K_Das]

I need to measure in range 100-165°C. Need not so much accurate but not more than 5% tolerance. I tried with the code I posted.

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:-(.

Now suggest me what the way I can do a clean measurement?

 

[jayanth.devarayanadurga]

For accurate measurement you need Constant Current Source and amplifiers.

https://www.electro-tech-online.com...-constant-current-source-pt100-circuit-3.html