ASTM E816 is the standard test method for calibration of pyrheliometers by comparison to reference pyrheliometers. This test method covers two types of calibrations. One is calibration of a secondary reference pyrheliometer, and the second is transfer of calibration. This method provides calibration procedures and details the calibration hierarchy. It is especially used for reference pyrheliometers with field angles of 5 to 6 degrees.
ASTM E816 Standard Test Method for Calibration of Pyrheliometers by Comparison to Reference Pyrheliometers
What is ASTM E816?
What is the Scope of ASTM E816?
The ASTM E816 test method covers calibrating pyrheliometers by comparison to reference pyrheliometers. It uses only sunshine for calibration. Measurements from this method are used for quality control, safety assurance, performance evaluation, and research. The specifications and working capabilities of the materials can be determined. This helps specify their applications and enhance their products to meet global standards.
ASTM E816 Equipment and Sample Preparation Guide
Primary and secondary reference pyrheliometers that are not field instruments are used for calibration. Exposure of these instruments to sunlight is kept limited to calibration or intercomparisons. These reference instruments are stored in an isolated cabinet or room equipped with standard laboratory temperature and controlled humidity conditions.
Specimen size should be as per the requirements. In this case, the reference and field pyrheliometers shall be nonselective over a range from 0.3 to 4-μm wavelength.
ASTM E816 Testing Procedure and Requirements
The test apparatus is set up by mounting the self-calibrating absolute cavity pyrheliometer on the sun-tracking mount. The distance between the pyrheliometers must not exceed 20m. The instruments are then connected to the digital voltmeter. Pyrheliometers are adjusted properly, and the quartz aperture of the secondary pyrheliometer is cleaned. The output voltage and irradiance are measured within a 1-sec interval. The standard deviation of the measured values is determined, and the zero offsets of all pyrheliometers are recorded.
ASTM E816 Analysis Results and Interpretations
The calibration factors are determined by applying the equation in which E stands for the irradiance values, and V stands for the voltage signals.
Updated on August 23, 2026
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