Fan Aspirated Temperature Sensor

The temperature sensor for my weather station is a commercial wireless temperature/humidity sensor that I have mounted in a commercial solar radiation shield. It has been in operation for a couple of years and seems to be reasonably accurate. The humidity sensor part did fail and the sensor had to be replaced. Despite being in the radiation shield the outdoor environment is hard on humidity sensors.

radshld1

Above is a picture of the commercial solar radiation shield with the wireless temperature/humidity sensor inside.

Another approach to protecting the sensor for solar radiation is to use a fan to provide a steady flow of external air. Essentially blowing away the hot air around the sensor. The processor that I am using to read the wireless weather sensors also has provisions for a wired temperature/humidity sensor which I have been using to monitor the conditions inside the instrument cabinet. I thought it would be interesting to compare the passive radiation shield with a fan aspirated shield.

I build a simple shield out of some 2″ PVC pipe and fittings.

fantemp1

The picture above shows the parts of the sensor. In the middle is the actual sensor mounted on a small PC board with a RJ11 connector. Above that is a 12VDC wall wart to power the fan. The 40 mm computer  fan to the left is mounted in a short section of 2″ PVC and glued in place. A length of telephone cable is used to connect the sensor to the processor. A PVC U fitting and a longer piece of PVC completes the sensor.

fantemp2

Above is a picture of the completed sensor mounted on my instrument platform. The fan draws air up the long tube and out the short tube. With both ends to the tube facing down it should help keep the rain and snow out.  The sensor is located near the middle of the U fitting.  It remains to be seen how long the fan and humidity sensor will last in this environment.

After it runs for a few days I will compare the performance of the two sensors.

6/22/2016 Comparison data between the two sensors shows that the fan aspirated sensor is affected by the sun more than the sensor in the shield. Next I will try a simple sun shade for the fan aspirated sensor.

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