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Eppley Precision Infrared Radiometer (PIR)

Eppley PIR The Eppley Precision Infrared Radiometer, or pyrgeometer, is designed for the measurement of downward or upwelling longwave irradiatance. There is no official ISO/WMO classification of pyrgeometers that are designed to measure the longwave (infrared) irradiance from the sky. The PIR has the same wirewound thermopile detector and temperature compensation circuitry as found in the Eppley SPP pyranometers. The Eppley PIR pyrgeometer has a shield and a body that is similar to the SPP. The dome is coated to filter the shortwave radiation. This thermopile detector is used to measure the "net" incident longwave irradiance and a case thermistor is used to determine the outgoing longwave radiation from the case. A dome thermistor is also included to measure the dome temperature to adjust for the thermal bias and provide more accurate results. The Eppley PIR pyrgeometer has a shield and a body that is similar to the Eppley SPP. The measurements from the PIR include, downward longwave irradiance, sky temperature, case temperature, and dome temperature.

Specifications

• Sensitivity: approximately 3 µV/Wm-2.
•
Spectral Range: approximately 4,000-50,000 namometers.
•
Temperature Response: ±.5% over ambient temperature range -30 to +50°C.
• Linearity: ±0.5%-2.
•
Response time: 5 second (95%).
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Weight: 7 pounds.
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Orientation: Change in tilt response is less than 0.5%.
Calibration change (stablity) is about 1% per year or better;.

For a PIR, the calibrations are done against the World Infrared Standard Group (WISG) International Practical Temperature Scale (IPTS). Getting an exact value for the downward irradiance is under discussion, although a more precise value is being defined. For now, these values are to be considered a best estimate.

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© 2022, UO Solar Radiation Monitoring Laboratory.
Last revised: March 29, 2022.

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