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

SQ-214: Amplified 4-20 mA Sun Calibration Quantum Sensor

The SQ-214 is an amplified sensor with a 4-20 mA output and exhibits excellent cosine response. The sensor was designed for use in environments with significant background electrical noise that can be found in many industrial applications.

The sensor measures photosynthetically active radiation and is calibrated for use in sunlight. The sensor housing design features a fully potted, domed-shaped head making the sensor fully weatherproof and self-cleaning. Photosynthetically active radiation (PAR), or photosynthetic photon flux (PPF), is the wavelength range from 400 to 700 nanometers and is strongly correlated with plant growth. Gardeners, greenhouse managers, growth chamber users and salt-water aquarists measure PAR to insure optimal specimen health.

Power Supply: 5-36 V DC with a maximum current drain 22 mA (2 mA quiescent current drain)
Sensitivity: 0.0064 mA per µmol m-2 s-1
Calibration Factor: 156 µmol m-2 s-1 per mA (reciprocal of sensitivity)
Calibration Uncertainty: ± 5%
Measurement Repeatability: < 1%
Non-stability (Long-term Drift): < 2% per year
Non-linearity: < 1% (up to 2500 µmol m-2 s-1)
Response Time: < 1 ms
Field of View: 180°
Spectral Range: 410 nm to 655 nm (wavelengths where response is greater than 50% of maximum)
Directional (Cosine) Response: ± 5% at 75° zenith angle
Temperature Response: 0.06 ± 0.06% per °C
Operating Environment: -40 to 70°C, 0 to 100% relative humidity, Can be submerged in water up to depths of 30m
Dimensions: 2.4cm diameter and 2.8cm height
Mass: 140g (with 5m of lead wire)
Cable: 5m of shielded, twisted-pair wire. Santoprene rubber jacket (high water resistance, high UV stability, flexibility in cold conditions). Pigtail lead wires
Warranty: 4 years

Radiation that drives photosynthesis is called photosynthetically active radiation (PAR) and is typically defined as total radiation across a range of 400 to 700nm. PAR is often expressed as photosynthetic photon flux density (PPFD); photon flux in units of micromoles per square meter per second (µmol m-2 s-1, equal to microEinsteins per square meter per second) summed from 400 to 700nm (total number of photons from 400 to 700nm). While Einsteins and micromoles are equal (one Einstein = one mole of photons), the Einstein is not a SI unit, so expressing PPFD as µmol m-2 s-1 is preferred.

The acronym PPF is also widely used and refers to the photosynthetic photon flux. The acronyms PPF and PPFD refer to the same parameter. The two terms have co-evolved because there is not a universal definition of the term “flux”. Some physicists define flux as per unit area per unit time. Others define flux only as per unit time.

Sensors that measure PPFD are often called quantum sensors due to the quantised nature of radiation. A quantum refers to the minimum quantity of radiation, one photon, involved in physical interactions (e.g: absorption by photosynthetic pigments). In other words, one photon is a single quantum of radiation.