LM 35

[vick5821]

Anyone here have experince using LM 35 Temperature sensor ? How does it able to sense heat ?

Can I use it without microcontroller ?

Thank you

 

[TedA]

vick5821,

The LM35 is an analog part. It does not require any microcontroller.

Have you looked at the data sheet?

http://www.datasheetarchive.com/dl/Datasheets-22/DSA-423890.pdf

"The LM35 series are precision integrated-circuit temperature
sensors, whose output voltage is linearly proportional to the
Celsius (Centigrade) temperature."

You can hook a voltmeter to the LM35 output and read off the temperature.

If you should want to use it with a microcontroller, you will need to involve an ADC or one or more voltage comparators.

The temperature is sensed using a special sort of band-gap voltage regulator circuit that is designed to have a very linear and predictable response to the temperature of the chip.

Ted

 

[vick5821]

Then can it performs the function like thermister or it just sense heat and display it ?

 

[(*steve*)]

It doesn't do any displaying, but in some sense it is like a thermistor.

An output voltage on the LM35 changes as temperature changes.

A thermistor, if supplied with a constant current will do a similar thing.

HOWEVER, the LM35 is far more linear and has an output voltage which is more tightly specified than a thermistor's change in resistance.

 

[vick5821]

It doesn't do any displaying, but in some sense it is like a thermistor.

An output voltage on the LM35 changes as temperature changes.

A thermistor, if supplied with a constant current will do a similar thing.

HOWEVER, the LM35 is far more linear and has an output voltage which is more tightly specified than a thermistor's change in resistance.

So I can do a heat detector circuit using LM 35?

 

[(*steve*)]

You can do a TEMPERATURE detector using an LM35 (a thermometer). Heat is a totally different thing.

 

[vick5821]

if heat i need to use thermister? but got heat the temperature increases right? so interelated?

 

[(*steve*)]

No, thermistors and other things detect temperature.

Heat is the total amount of thermal energy, temperature is the average thermal energy.

For example, consider a hot cup of tea and a warm bath. The first has a higher temperature, but the latter contains more heat.

I'm not sure there's a way to directly measure heat.

 

[vick5821]

i want to do a heat detector circuit, so can use LM35?

 

[(*steve*)]

You can do a TEMPERATURE detector using an LM35 (a thermometer). Heat is a totally different thing.

 

[vick5821]

I am doing a circuit that can detect open burning.When someone do open burning, it will sense the temperature rise and buzer will sounds. So is it apporpiate to use LM 35?

 

[(*steve*)]

It will only work if the temperature of the LM35 is increased by the radiated, convected, or conducted heat.

So if the hot air from the combustion is directed toward the LM35, it will detect it.

However, if you're wanting to detect temperature remotely then you may need a different device.

 

[vick5821]

It will only work if the temperature of the LM35 is increased by the radiated, convected, or conducted heat.

So if the hot air from the combustion is directed toward the LM35, it will detect it.

However, if you're wanting to detect temperature remotely then you may need a different device.

You mean I have to bring the heated thing near to LM 35 ? Or else it won detect the rise in temperature from a distance ?

 

[(*steve*)]

No, it reports its own temperature. Just like a thermometer.

This will tell you how to detect heat at a distance. Note that you're detecting black-body radiation, and not temperature directly. The temperature is related to the distribution of the wavelengths emitted.

Perhaps you should also read this.

 

[vick5821]

OMG..just like a thermometer..means have to bring quite near to the heat source to have a significant change i voltage

 

[(*steve*)]

Check my edits

 

[vick5821]

Using PIR sensor ? Isnt that it is used as to detect motion ?

 

[vick5821]

What other sensor that can be used to detect heat ?

 

[davenn]

The PIR would be the closes thing to be able to be used to detect heat ( temperature) at a distance

also have a look at this wiki page


Dave

 

[(*steve*)]

Using PIR sensor ? Isnt that it is used as to detect motion ?

Yes, but:

Designs have been implemented in which a PIR circuit measures the temperature of a remote object.https://en.wikipedia.org/wiki/Passive_infrared_sensor#cite_note-PIR_Thermometer_Tsai_2003-2 In such a circuit, a non-differential PIR output is used.