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Enabling better global research outcomes in soil, plant & environmental monitoring.

Apogee SQ-500 Quantum Sensor

Apogee Instruments' new Quantum Sensor, the SQ-500, has an improved spectral response, providing accurate PAR/PPFD measurements under all light sources, including LEDs.

Rugged Design: The head is submersible and suitable for use in all climate conditions. Patented domed shaped sensor head (diffuser and body) facilitate runoff of dew and rain to keep the sensor clean and minimize errors caused by dust blocking the radiation path. Sensors are housed in a rugged anodised aluminium body and electronics are fully potted.
Excellent Cosine Response: Sensors measure PPFD with a cosine response accurate within ±5% at 75° zenith angle.
Refined Spectral Response: The improved spectral response of the SQ-500 increases the accuracy of LED measurements, making it ideal for use with both natural and electric light sources.
Accurate, Stable Measurements: Calibration in controlled laboratory conditions is traceable to a NIST lamp. Quantum sensors are cosine-corrected, with directional errors less than ± 5% at a solar zenith angle of 75°. Long-term non-stability, determined from multiple replicate quantum sensors in accelerated aging tests and field conditions, is less than 2% per year.
Typical Applications: PPFD measurement over plant canopies in outdoor environments, greenhouses and growth chambers, and reflected or under-canopy (transmitted) PPFD measurements in the same environments. Quantum sensors are also used to measure PPFD in aquatic environments, including salt water aquariums where corals are grown.

Power Supply Self-Powered
Output Sensitivity 0.01 mV per μmol m-2s-1
Calibration Factor (reciprocal of output) 100.0 μmol m-2s-1 per mV
Calibration Uncertainty ± 5%
Output Range 0 to 40 mV
Measurement Range 0 to 4000 μmol m-2s-1
Measurement Repeatability less than 0.5%
Long-term Drift Less than 2% per year
Non-linearity Less than 1% (up to 4000 μmol m-2s-1)
Response Time less than 1 ms
Field of View 180°
Spectral Range 389 to 692 nm, ± 5 nm (wavelengths where response is greater than 50% of maximum)
Spectral Selectivity Less than 10% from 412 to 682 nm ± 5nm
Directional (Cosine) Response ± 5% at 75° zenith angle
Azimuth Error Less than 0.5%
Tilt Error Less than 0.5%
Temperature Response -0.11 ± 0.03% per °C
Uncertainty in Daily Total Less than 5%
Detector Blue-enhanced silicon photodiode
Housing Anodised aluminium body with acrylic diffuser
IP Rating IP68
Operating Environment -40 to 70°C; 0-100% relative humidity; can be submerged in water up to depths of 30m
Dimensions 24mm diameter, 35mm height
Mass 100g (with 5m of lead wire)
Cable 5m of shielded, twisted-pair wire; additional cable available in multiples of 5m; santoprene rubber jacket (high water resistance, high UV stability, flexibility in cold conditions); pigtail lead wires
Warranty 4 years against defects in materials and workmanship

Screen Shot 01-12-16 at 04.42 PM

Mean cosine response of seven Apogee SQ-500 quantum sensors. Cosine response measurements were made on the rooftop of the Apogee building in Logan, UT.

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Cosine response was calculated as the relative difference of SQ-500 quantum sensors from the mean of replicate reference quantum sensors (LI-COR models LI-190 and LI-190R, Kipp and Zonen model PQS 1). The red data are AM measurements; the green data are PM measurements.

Screen Shot 01-12-16 at 09.12 AM

Mean spectral response measurements of six replicate SQ-100 and SQ-500 series quantum sensors. Spectral response measurements were made at 10nm increments across a wavelength range of 300 to 800mm in a monochromator with an attached electric light source. Measured spectral data from each quantum sensor were normalised by the measured spectral response of the monochromator/electric light combination, which was measured with a spectroradiometer

Spectral Errors of Commercial Quantum Sensors

Radiation Source Apogee
SQ-500
Apogee
SQ-110
SQ-120
LI-COR
LI-190
Kipp & Zonen
PQS 1
Sun (Clear Sky) -2.2 0.0 -0.4 -1.0
Sun (Cloudy Sky) -1.7 1.4 -0.2 -1.3
Sun (Reflected from Deciduous Leaves) -2.0 4.9 -0.8 1.1
Sun (Transmitted below Wheat Canopy) -1.1 6.4 -0.1 -0.3
Cool White Fluorescent (TS) 0.0 0.0 0.0 0.0
Metal Halide 0.9 -3.7 0.2 -1.7
Ceramic Metal Halide -0.3 -6.0 0.4 -0.7
High Pressure Sodium 0.0 0.8 1.3 1.4
Red/Blue LED (16% 444nm, 84% 667nm peaks) -3.4 – 65.3 3.5 -1.8
Red/White LED (6.5% 436nm, 4.5% 531 nm, 89% 668nm peaks) -3.0 -60.3 2.6 -1.7

Spectral errors are theoretical errors calculated from sensor spectral responses (Apogee SQ-100 and SQ-500 series shown in graph above) and spectral output of radiation sources (measured with a spectroradiometer). Only spectral errors are listed in the table. Calibration, cosine, and temperature error can also contribute to measurement error.

Calibration Traceability

Apogee Instruments SQ-500 series quantum sensors are calibrated through side-by-side comparison the the mean of four Apogee model SQ-500 transfer standard quantum sensors under high output T5 cool white fluorescent lamps. The transfer standard quantum sensors are calibrated through side-by-side comparison the the mean of at least three LI-COR model LI-190 reference quantum sensors under high output T5 cool white fluorescent lamps. The reference quantum sensors are recalibrated on a biannual schedule with a LI-COR model 1800-02 and quartz halogen lamp, traceable to the National Institute of Standards and Technology (NIST).