I want to build a low cost (not very accurate but with allowable margin of errors) solar irradiance sensor for my weather station using a photo transistor, but I am looking for the method of calibration for it using certain algorithm to also find a correlation with the accurate solar cell based irradiance sensor. Or can I achieve the correct calibration using the data sheet of the accurate irradiance sensor? Need suggestions.
Dear Sambit,
May be the best mode of operation of the phototransistor is to add a small collector resistance in the collector path to sense the collector current. The voltage cross this collector resistance can be amplified and the voltmeter can be calibrated to measure the solar irradiance.Here there are two methods to calibrate this voltmeter either by using the data sheet information of the the collector current at different solar irradiance values or using a standard solar cell to measure directly the solar irradiance by sensing its photocurrent in the manner used with the transistor.
Using the standard solar cell for calibration is more realistic than data sheet as the light source used in the data sheet may have different spectral power distribution other than the incident solar radiation. I mean one important issue to consider for the calibration is that one has to consider the power spectral distribution of the light source.
Best wishes
As Abdekahim states, you have to be very sure of your spectral responses for your calibration to be meaningful. It is quite amazing how far out of calibration you can get if the spectral responses of the test and 'calibrated' cells are different! Best wishes!
The linearity of Yours transistor has a great value. You can test it's linearity by rotation detecor relative to sun beam direction with the help of stepper motor, or servo with simlplest Arduino circuit. Angel dependence will be near cosA.
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