LM35 Temperature Recorder article.

The LM-35 device provides an ideal way to accurately measure temperature.

The LM-35 IC is a precision temperature measuring IC linearized to output 10mV per degree Centigrade.

Note: The LM34 IC (a companion device) outputs 10mV per degree Fahrenheit.

Packages

The LM35 comes in four different packages TO-46, SO-8, TO-92 and TO-220 and uses three pins (power ground and output).

The LM34 is not packaged in a TO-220 case only TO-46, SO-8 and TO-92.

The smallest packages TO-46 and TO-92 use the same space as a standard transistor. This makes the LM-35 or LM-34 easy to use since, along with a battery, you can just hook it up to a digital volt meter (DVM) and read the temperature directly.

Example output

For instance if the temperature was 25 degrees Centigrade then the LM-35 would output a voltage of 250mV so setting the DVM to a 2 volt range would allow you to see the current temperature directly (over the whole of the LM35 temperature range).

Power supply

The LM35 requires a voltage supply in the range 4V to 30V so it's just as easy to use in a 5V processor system as it is to use with a DVM and a standard 9V battery.

Range

The LM35 measures from -55º to +150ºC.
The LM34 measures from -50º to +300ºF

Note: You need to check the exact part number to get the full range as you can buy LM-35 that only cover the range 0º to +100ºC; similarly for the LM-34.

Accuracy

The LM35 is guaranteed accurate to ±¼ºC at 25ºC. And ±¾ºC over the range -55º to +150ºC.

The LM34 is guaranteed accurate to ±½ºF at 77ºF. And ±1½ºF over the range -50º to +300ºF.

These devices make temperature recorder measurements a trivial task since you don't need to linearize the output and they provide directly readable output on a DVM.

Temperature recorder

It's also quite an easy task to read the LM-35 (34) using an ADC and if you use one of the modern microcontrollers with a built in ADC you can make a temperature logging device. You can set this to measure temperature at timed intervals to give a picture of temperature fluctuations wherever the device is placed.

There's an LM35 project here to do just that.

The DS18B20

Another device that is worth considering is the DS18B20 which is a Dallas 1-wire device and although more costly than the LM-35 (34) it is a long distance networked sensor (you can have multiple 18B20's (or other 1-wire devices) attached to the same wire).

The 18B20 is more robust than the LM-35 since it outputs a purely digital signal in response to a master control query and it outputs this signal over extremely long distance which is impossible with the LM-35. Again a microcontroller is the ideal way to control it.