LM35 temperature sensor for human body temperature measurement

[Lathas]

How can I measure body temperature using LM35; should I touch the package body of LM35 directly to measure the temperature? How long do I need to keep touching the part before it gives a change in voltage output?

 

[andre_luis]

Re: body temperature measurement using LM35

I would not recommend using an analog output based sensor for temperature measurement in 'long' distances - not onboard, specially if the A/D conversion is not performed locally in the probe itself.

I suggest to consider the possibility of using a model based on SPI communication standard, or even I2C, although this one is more suscptible to electromagnetic interference induced in wiring.

 

[ravindragudi]

Re: body temperature measurement using LM35

It is required for the medium to be in contact with the package of the sensor to accurately measure the temperature of the medium. The time required by the sensor to provide stable and correct output varies with medium. Attached is the snapshot from DS. So it may be expected that (my own guess ) one has to wait for more than a minute to have a stable output from LM35 for the human body temp measurement. But this can be experimented against a known surface of definitive temp.

But in my view, instead of using a LM35 for human body temp measurement, thermistor is better suited. That too with carefully selected and designed probe having the thermistor in it.

I think the standard medical devices use max of 60 sec to finish measuring the temp.

 

[andre_luis]

Re: body temperature measurement using LM35

I still find some drawbacks on using analog sensors for remote sensing for that application, unless cabling is properly shielded and twisted. The LM35 provides 10mV/C degrees, and considering that the resolution for human temperature is normally assessed in the range of 0,1C degrees, this means that the noise expected should not exceed 1mV.

 

[vfone]

Yes, for body temperature measurement the package sensor should touch the body.
The metal case LM35 works better in this regards than the plastic package type. But they are more expensive.

http://www.digikey.com/product-search/en?mpart=LM35DH/NOPB&vendor=296

http://danyk.cz/lm35_en.html
**broken link removed**

 

[chuckey]

You need to do some serious work in making the probe and cabling, so that it can be sterilised. You would not want your gizmo to transfer diseases, would you?
Frank

 

[John Mossbacher]

Simple latex or poly-plastic compounds can be bought at medical wholesale sites for an usually affordable price if you shop around.