Hello everyone,
I have been conducted some experimental tests by the time and I have faced some measurement errors. I have 2 pyranometers which form different companies but much similar in terms of technical specifications, yet they show different solar power even if they are located right beside of each other! what is the problem? which one shall I trust?
Kind Regards,
Amin
Dear Amin,
Can you give us an example of yoru measurements? If the difference is small, of about 10-20 W/m2, then you can take the mean value as the most correct. If the deviation is greater, then you have to find which shows wrong results.
Best Regards,
E. Bellos
Dear Amin,
Can you give us an example of yoru measurements? If the difference is small, of about 10-20 W/m2, then you can take the mean value as the most correct. If the deviation is greater, then you have to find which shows wrong results.
Best Regards,
E. Bellos
I think the best thing to do is to calibrate your 2 pyranometers in front of a same standard source. It is the only way to obtain a right radiometric measurement.
You can also refer to the user manual provided by the constructor of your instruments to find the relative error referred by the manufacturers.
Best regards
Dr. D. Gillotay
Yes of course the calibration is the best way for taking the most accurate results
Please know that different instruments/ semsors made by different manufacturers have different accuracy levels as well as different reliability over time. Hence, you will never get the same measurements.
The only way around this issue is to use at least three sensors and use a voting logic that can compare the measurements and take an average value. The voting logic can also eliminate sensors that give outlier measurements.
Hope this helps answer your question.
Professor Yehia Khalil, Yale University, USA
Fellow of the University of Oxford, United Kingdom
There are a lot of discussions and publications about pyranometers on ResarchGate
Article Pyranometer Thermal Offset: Measurement and Analysis
Article Uncertainty calculations in pyranometer measurements and applications
Dear Mr. Amin.
1. Make the calibration of the 2 sensors from the same source.
2. Take the average of at least 10 readings.
3. From my experience when we have 2 instruments it will never give the same readings (ERROR %)
4. Check if one of them is fail.
5. Change the connection i mean replace the 2 sensors and notice the readings.
6. U can add % of reading to the sensor which we think its not wright.
Kind regards
As everyone knows, in a pyranometer, the measurement of solar radiation intensity is basically effected by measuring the temperature of the absorber plate. Thermopile (thermo couple) temperature sensors are usually used to measure the temperature. The thermocoules need frequent periodic calibration to ensure reliability of the measured value. In any case (+/-)2 to 3% uncertainty is expected. (The word error is not used because it is a misnomer in measurement science, at present. The appropriate word is uncertainty.)
If the difference between the two instruments is less than some 2 - 3%, as rightly said one may take the average.
But, always, the best approach is first calibrate the instrument and do the measurement. And while taking the measurement using a calibrated instrument, take multiple reading in identical conditions and finally take the average.
For calibration, one approach a temperature calibration facility. Alternately you may refer the paper available at "http://www.sciencedirect.com/science/article/pii/S0038092X03001245", also.
- Badges
- Science topic