Using Your Apogee Instruments Pyranometer

Conversion Factors

The pyranometer sensor uses a silicon cell to yield a millivolt output. This output is multiplied by a conversion factor to yield W m-2.

Amplified pyranometer sensors use smaller conversion factors to match their increased mV outputs. For 5 V models, the conversions factor is 0.25; for 2.5 V models the conversion factor is 0.5.

Pyranometer sensors measure the shortwave radiation reaching the Earth's surface, measured in Joules m-2 s-1 or Watts m-2.

Taking Handheld Readings

1. Press the Power button once to turn the pyranometer meter on (indicated at right inside red box).

2. Handheld meters should be held with top of meter level to horizon careful not to shade the sensor in any way. Separate pyranometer sensors should be mounted on a horizontal surface.

3. The number displayed is in Watts m-2.

ClearSky Calculator

The ClearSky Calculator is a free web-based tool that estimates the intensity of shortwave radiation under a clear sky, falling on the Earth’s surface at any time of day in any location around the world. The calculator is primarily used to determine the need for recalibration of solar radiation sensors. Radiation estimates produced by the calculator are most accurate near solar noon during summer months. In a recent study, calculator accuracy was reported to be ± 3 percent when used under optimal conditions∗; sensitivity to required input parameters was also reviewed in the study. The calculator is found at

∗ASCE Standardized Reference Evapotranspiration Equation. American Society of Civil Engineers. Reston, Virginia, USA. 2005.

Wiring the Sensor

Attach the sensor to a meter or datalogger capable of displaying or recording a mV output.

The model, serial number, production date, and conversion factor are located on the sensor cable.

*Please see the actual product manual for the wiring diagram for the SP-214

Mounting the Pyranometer

Mount the pyranometer sensor to a solid surface with the nylon mounting bolt. The sensor should be mounted level for the most accurate measurements. We recommend using our leveling plate (AL-100).

The pyranometer sensor should be mounted with the cable pointing toward true north in the northern hemisphere or true south in the southern hemisphere to minimize azimuth error. The azimuth error is typically less than 1%.