Pyranometer ventilation unit VU01

Overview
VU01 is a high-quality ventilation unit for use with pyranometers and pyrgeometers. Its purpose is to improve the dependability of the measurement. Measurement accuracy improves, because offsets are reduced.

Key features
• Offsets reduction: Promotes thermal equilibrium between all radiometer components, reducing the "zero offset a" of an SR20 pyranometer to 2.5 W/m² (at 0 W heating).
• Dew, frost, and snow mitigation: Continuous airflow prevents dew and frost deposition; optional heating accelerates droplet evaporation and snow sublimation.
• High airflow performance: High ventilator power generates a strong, reliable airflow over both the instrument body and dome.
• Optional two-level heating: Equipped with two onboard heaters providing 5 W or 10 W heating power at 12 VDC, activated via external relays or datalogger control.
• Fan rotation monitoring: Includes a fan status signal output allowing users to remotely monitor fan rotation and operation.
• Accessible maintenance: Features a removable dust filter accessible directly from the bottom of the unit for straightforward cleaning and replacement.
• International standards compliance: Built according to the recommendations of ISO/TR 9901 ("Field Pyranometers—Recommended practice for use") and the Baseline Surface Radiation Network (BSRN operations manual v2.1).
• Compact, snow-shedding footprint: Small footprint diameter of 0.17 m minimizes surface area and prevents snow accumulation.

Applications
• Photovoltaic (PV) system performance monitoring.
• High-accuracy scientific meteorological observations.
• Baseline Surface Radiation Network (BSRN) stations.
• Operations in extreme climates (tropical and polar environments).

Specifications
• Compatible instruments: SR20, SR20-D2, SR22, SR25, SR25-D2, IR20, IR20WS
• Compliance with standards: ISO/TR 9901, BSRN operations manual v2.1
• Rated operating power (unheated): 7.8 W at 12 VDC
• Rated operating voltage range: 10.8 to 13.2 VDC
• Heaters (optional use): 5 W and 10 W at 12 VDC
• Increase of air temperature: 0.5 °C (at 0 W heating), 1.0 °C (at 5 W heating), 1.5 °C (at 10 W heating)
• Zero offset a (SR20 ventilated): 2.5 W/m² at 0 W heating
• Additional offset by heating (SR20): -2 W/m² at 5 W heating; -4 W/m² at 10 W heating
• Additional offset by heating (IR20): 0 W/m² at 5 W heating; 0 W/m² at 10 W heating
• Fan status signal: Available (optional use)
• Rated operating temperature range: -40 to +70 °C
• Cable resistance: 0.3 Ω/m (2 x 0.15 Ω/m)
• Voltage drop at 10 W heating power: 0.12 V/m
• Footprint diameter: 0.17 m
• Standard cable length: 5 m

Options and accessories
• Standard cable length: 5 m
• Longer cable options: Available in multiples of 5 meters (taking cabling voltage drop into account)
• Replacement filter pack: Pack of five filters (model VU01F)