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# thermal response time of LM35 temp sensor??

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#### bhudu

##### Newbie level 3
HI...

I am thinking to use LM35 for temperature measurement of peltier element, where temperature will change rapidly. So, I need to use a sensor which will give fast response for change in temperature.
but I have seen the data sheet of lm35 for thermal response in still air graph, but I am not understanding clearly. so please can anyone help me...

what is the thermal repose time of lm35 and suggest some other temp sensor with fast response time.

thank you so much....

Hi,

I'd say the smaller the sensor ant the better the thermal connection, the faster the response time.

Although the LM35 is possible, there are other dedicated temperature sensors with more outout signal.

Klaus

Hi, thank you for the response

but It would be great if you give response time value..... I mean if temp is at 10 Celsius and suddenly the temperature changed 80 degrees, how long it will take to send the temperature value in seconds.

Hi,

With good thermal conductivity i'd expect a time constant of less than 2 seconds.

Klaus

Did you pay attention to the response time diagrams in the LM35 datasheet?

Thermal conductance, heat mass and fluid velocity all affect response time like an RC low pass filter. Fluid can be air (insulator) or oil (conductor)

Highest resistance is the TO-92 in still air of about 2 minutes, while the fastest in stirred oil s 2 seconds.

consider a 1 order approximation for step response as 1T to 63% 2T to 90% and 4T to 98% of the step.

Thank you all for enlightening me....Actually I am searching for this information in datasheet , but there is no graph stating about thermal response when the sensor is attached to metal. I need to show that LM35 have good thermal response for documentation. please can anyone suggest how do I can justify for using lm35.

What do you need it to be? Better than my previous answer?

Is the metal much heavier than the sensor attached to it?

Rise time index is a function of mass, area , specific heat and thermal resistance,
... which you dont have, so test it.
ok?

yogece

Points: 2