# Why there are different types of LM temperature sensors

Hey guys, what's up?

I've been making the same question for about a month: why there are 3 different types of temperature sensors that displays temperature in differente scales?

Just like the LM35 = Celsius, LM34 = Fahrenheit and the LM335 = Kelvin.

Why did they make those kinds of sensors?

Best regards.

Because there is a market for each?

Any range can easily be converted to any other range, especially digitally.
Kelvin - 273.15 = Celsius
((Kelvin - 273.15) * 9/5) + 32 = Fahrenheit
(Celsius * 9/5) + 32 = Fahrenheit

Analog-wise, like a mercury thermometer, it is just markings on a scale next to each other.

I live in the US. 32F is cold, but not bad if the wind is not blowing. 0F is cold!
If you were to say is is 273K, I’d have to see what that was in F to make sense of it.

If I were conducting scientific experiments, or doing engineering studies, than a range of 0C +/- 273C might make sense.
(For example, when I re-flow solder, I start at room temperature, ~23, level off for solder paste activation at 125-150C, then actually reflow at 183C to 195C. Bigger F numbers would work just as well, the solder paste itself doesn’t care).

For normal living, 0F to 100F matches my expected external temperatures. 72F to 76F is pretty confortable. A degree or two combined with humidity makes a big difference.

For those outside the US, that range might be -18C to 38C. 22.2 to 24.4 seems like a mouthful to describe the comfortable range to me. Guess it depends on what you grew up with. Saying “23.5 and 60% humidity” just seems awkward to me.

Also, with those types of sensors, you only need a voltmeter and 4 or 5 volt power supply to read temperature, if your LM35 reads 0.28 volts, multiply that by 100 and you have 28 degrees C, if your LM34 reads 0.72 volts, X 100 = 72 F.

JCA34F:
Also, with those types of sensors, you only need a voltmeter and 4 or 5 volt power supply to read temperature

Yep, those sensors were designed in and for the analogue times (50 years ago).
Best to NOT use them in the digital world.

There are much better and easier to use digital (I2C, One-wire) sensors now.
Leo…

Yep, those sensors were designed in and for the analogue times (50 years ago).

But I still have a Simpson 260.

frbabos:
I've been making the same question for about a month: why there are 3 different types of temperature sensors that displays temperature in differente scales?

Why are there different rulers and scales and for metric and imperial? Obviously because people use
and want both.

This is also the reason very few temperature sensors use degrees Newton, because no-one uses that
scale any more.

Yes you can always convert the output, having a human-meaningful output scale makes it easier to
work with (you can check a bunch of sensors with a multimeter easily for instance)

There are also many temperature sensors that have an output dependent on the technology used,
such as PT100 and thermcouples, thermistors...

As to why some people cling onto non-SI units at all, that's another question...