Calibration heat flux sensor HFP01SC

Overview
HFP01SC self-calibrating heat flux sensor is a heat flux sensor for use in the soil. It offers the best available accuracy and quality assurance of the measurement. The on-line self-test verifies the stable performance and good thermal contact of sensors that are buried and cannot be visually inspected and taken to the laboratory for recalibration. The self-test also includes self-calibration which compensates for measurement errors caused by the thermal conductivity of the surrounding soil (which varies with soil moisture content), for sensor non-stability and for temperature dependence.

Key features
• On-line self-test and self-calibration: Incorporated film heater activates at regular intervals to perform a self-test, verifying sensor-to-soil contact and generating a newly measured sensitivity valid for immediate local conditions.
• Compensates for deflection errors: Corrects for errors caused by the mismatch between soil and sensor thermal conductivity, variations in soil moisture content, temperature dependence, and sensor aging.
• No removal needed for recalibration: Designed to be left in the soil long-term so soil properties remain representative, eliminating the need to excavate sensors and take them to a laboratory to verify stable performance.
• Low thermal resistance: Features low thermal resistance (81 x 10⁻⁴ K/(W/m²)) to minimize disturbance to the natural heat flow.
• Standardized guard area: Equipped with a large passive guard area around the sensing region, adhering to ISO 9869 requirements.
• High sensitivity and low electrical resistance: Offers a nominal sensitivity of 60 x 10⁻⁶ V/(W/m²) for a high signal-to-noise ratio in low-flux environments, paired with low electrical resistance to prevent electrical noise pickup.
• Outdoor ruggedness: Rated IP67 with heavy-duty cabling and robust potted covers, providing essential durability for permanent underground installations.
• Traceable factory calibration: Calibrated traceable to international standards following the recommended practice of ASTM C1130.

Applications
• High-accuracy scientific measurement of soil heat flux requiring top-tier data quality assurance.
• Surface energy balance and surface energy flux experiments.
• Long-term agricultural and climatological soil monitoring networks.
• Soil thermal property and soil moisture dynamics research.

Specifications
• Measurand: Soil heat flux [W/m²]
• On-line functionality testing: Self-test including self-calibration
• Measurement range: -2000 to 2000 W/m²
• Sensing area: 8 x 10⁻⁴ m²
• Sensor thermal resistance: 81 x 10⁻⁴ K/(W/m²)
• Sensitivity (nominal): 60 x 10⁻⁶ V/(W/m²)
• Rated operating temperature range: -30 to +70 °C
• IP protection class: IP67
• Film heater resistance: 100 Ω ± 10 %
• Film heater rated power supply: 9 to 15 VDC
• Interval between self-tests: 6 hr
• Heating interval duration: 180 s
• Power consumption (daily average): 0.02 W
• Calibration traceability: Traceable to international standards (ASTM C1130 practice)
• Data acquisition and control requirements: 1 x millivolt measurement (heat flux), 1 x current measurement or voltage over current-sensing resistor (heater current), 1 x relay with 12 VDC nominal output (heater switching)
• Standard cable length: 2 x 5 m

Cable length options
• Standard cable length: 2 x 5 m (both cables)
• Longer cable options: In multiples of 5 m (10, 15, 20 m) and multiples of 10 m (30, 40 m) for both cables