SparkFun Forums

[aaaahern]

Hi,

I bought a Infrared Thermometer - MLX90614 sensor and want to use it to detect water temperature. In order to get accurate temperature, I put it below a paper cup and the sensor touch with the bottom of the paper cup. It works fine at beginning, but once the ambient temperature is higher than 97F, the read() operation will return fail. If I detach them and cool down the sensor, it works again.

Is it an individual problem? The description says it works find within -40~85C. https://www.sparkfun.com/products/9570

Have anyone meet this problem before?

[aaaahern]

The technique support didn't know the reason. So I post more detail and the data I got.

I put the sensor on the bread board. It works fine in room temperature.

1.jpg

I put the paper cup on top of the IR sensor. What inside the cup is just hot water. The temperature of hot water is up to 160F. The sensor possibly touch with the bottom of the paper cup. No water is leaked out.

2.jpg

The green dot and red dot represent the data of IR sensor. As you can see, it can detect high object temperature, but once the ambient temperature higher than 100F, it didn't work.

3.png

[DanV]

read this:
http://www.google.com/url?sa=t&rct=j&q= ... GC5LAWpg-g

it says:
It is very important for the application design to understand that these accuracies are only guaranteed and achievable when the sensor is in thermal equilibrium and under isothermal conditions (there are no temperature differences across the sensor package). The accuracy of the thermometer can be influenced by temperature differences in the package induced by causes like (among others): Hot electronics behind the sensor, heaters/coolers behind or beside the sensor or by a hot/cold object very close to the sensor that not only heats the sensing element in the thermometer but also the thermometer package.

[aaaahern]

read this:
http://www.google.com/url?sa=t&rct=j&q= ... GC5LAWpg-g

it says:
It is very important for the application design to understand that these accuracies are only guaranteed and achievable when the sensor is in thermal equilibrium and under isothermal conditions (there are no temperature differences across the sensor package). The accuracy of the thermometer can be influenced by temperature differences in the package induced by causes like (among others): Hot electronics behind the sensor, heaters/coolers behind or beside the sensor or by a hot/cold object very close to the sensor that not only heats the sensing element in the thermometer but also the thermometer package.

I tried to keep a small distance(~2cm) between the sensor and the bottom of the paper cup. The hot water still heating up the sensor and it still have the problem. If I need to use it to detect the ambient temperature, the thermometer package must be heated up right? How can it works in -40~125C temperature range without heating up the sensor package?

[jremington]

You need to mount the sensor in such a way that the sensor package is kept at ambient temperature, either by convective air flow or using a heat sink.

It is important to have a 100 nF bypass capacitor directly across the power pins of the sensor.

Your crude mounting arrangement is guaranteed to fail.