10 August 2011
7 Habits of Highly Effective Scientists
One of the most important things in any study is the fundamental quality of your measurements. So here are seven steps to help you make better measurements with your Apogee solar radiation sensors.
1. Situate sensors in ideal conditions
Special care needs to be taken when placing solar sensors for long-term outdoor measurements. Sensors need to be placed where they won’t be in the shadow of any surrounding objects such as trees or power poles. Avoid locations where dripping or splashing can occur on the sensors, or where birds may perch.
2. Correctly Mount the Sensor
Solar radiation sensors should be mounted level to help maintain accurate and consistent measurements from day to day, month to month, and year to year. The cable should be mounted pointing toward true north in the northern hemisphere or true south in the southern hemisphere to minimize azimuth error.
3. Verify wiring connections
Make sure that your wiring is secure and properly connected. Intermittent, and often frustrating, problems can arise when the wiring does not make a good contact with the controller/datalogger being used.
4. Ground the shield wire
Apogee’s solar radiation sensors all come with a cable shield that should be grounded to help mitigate electromagnetic interference (EMI). The shield wire is usually the clear or gray wire.
5. Clean Sensors
Our sensor has a round top to make it self-cleaning, but an occluded diffusion disk is still a common cause of low or erratic readings. Dust and dirt can be cleaned from the sensor’s disk using a non-abrasive cloth or cotton swab sprinkled with deionized water or rubbing alcohol. Calcium deposits, from irrigation water leave a thin white film on the surface that can be removed with a dilute acid such as vinegar.
6. Know what you are measuring
Being familiar with the sensor’s specifications, operation, and measurements will help you to recognize errors before days or even week’s worth of data becomes unreliable and unusable. Ensure your datalogger program is using the correct multiplier and that the channels in the program match the channels used for the sensor. Many applications benefit from 50 or 60 Hertz noise rejection. A simple method of troubleshooting the datalogger program is to swap a working sensor with a problematic sensor to see if the problem goes away.
7. Calibrate your sensors when needed
We recommend a recalibration cycle of every two to three years for our solar radiation sensors, particularly when using the sensor in extremely hot, outdoor applications. But rather than guessing when you might need a recalibration, we recommend a cheaper, faster method. Our Clear Sky Calculator is designed to calculate the intensity of radiation falling on a horizontal surface, at any time of day, in any location in the world. The calculator outputs a value that can be directly compared to the output of your sensor. For best accuracy, comparisons should be made on clear, non-polluted, summer days within one hour of solar noon. In these conditions the Clear Sky Calculator is within 2% of the actual radiation value.