# Contact temperature sensor [closed]

I need a contact temperature sensor to get the temperature of a container.

Anything like LM35 which I found from google search gives me ambient temperatures. Can anyone suggest an easy to use contact temperature sensor? Accuracy as high as possible! I am going to use it with an Arduino Due, if that information is relevant.

## closed as off-topic by PeterJ, Null, Nick Alexeev♦Sep 11 '15 at 8:33

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• "Accuracy as high as possible!" That is not a requirement, that is a pipe dream. Are you realy prepared to pay \$ to get 0.01 degree accuracy? – Wouter van Ooijen Feb 8 '15 at 18:26

You can use the LM35 version that comes in a TO-220 and bolt it to the container, then thermally insulate the exposed side.

Note that the tab is electrically connected so you may need to add an (electrical) insulator pad.

There are many, many other ways of measuring surface temperature in specific circumstances (thermocouples, thin-film RTDs, etc.) but this is very simple and may work for you, absent specific requirement numbers.

• I want to measure temperature vs time for a metal glass which will have milk in it. It would be a 200 mL glass with 3 inch diameter approx. Could you suggest a better way? If there is something which gives better precision and accuracy? Thanks for advice – Cheeku Feb 8 '15 at 18:47
• @Cheeku You must define the accuracy and precision you require or I'm not going to waste time mentioning any of the literally thousands of alternatives. – Spehro Pefhany Feb 8 '15 at 18:57

The LM34 / LM35 (Fahrenheit / Centigrade, respectively) analog output thermometers should do fine, as will the DS18b20 digital output ones. The key is to make sure they are in intimate contact with the surface you want to measure, and if the surface and ambient air temperatures are much different, the leads of the device, especially the plastic packaged ones, will have have a large effect on the reading and need to be thermally insulated from the ambient air.

This is discussed in the section "Typical Applications" of National Semiconductor's datasheet for the LM34. It will apply to any plastic-packaged thermometer since the wire leads will be much more thermally conductive than the plastic.

LM35 will do the job. The issue is not the sensor, but the way you use it. You must have good thermal contact with the element that you want to measure and isolation from the rest.

One way to do it is to insert the LM35 in a radiator (same as you would use to cool a LDO) that is soldered to the element to be measured, and have quite thin wires connecting your LM35 to your evaluation board.