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

SQ-320 Series Electric Calibrated Line PAR Sensors

Apogee line quantum sensors measure a spatial average of photosynthetically active radiation. The SQ-321 has a sensor bar with 10 sensors and is calibrated for use with electric lights. The sensor housing design features an integrated bubble level and is fully potted making the sensor weatherproof. 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.

Sensitivity: 0.2 mV per µmol m-2 s-1
Calibration Factor: 5.0 µmol m-2 s-1 per mV (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; maximum PPF measurement is 2500 µmol m-2 s-1)
Response Time: < 1 ms
Field of View: 180°
Spectral Range: 410 nm to 655 nm
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 30 m
Dimensions: 70 cm length, 1.5 cm width, 1.5 cm height
Mass: 375 g (with 5 m of lead wire)
Cable: 5 m of shielded, twisted-pair wire. Santoprene rubber jacket (high water resistance, high UV stability, flexibility in cold conditions). Pigtail lead wires
Power Supply: Self Powered
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 700 nm. PAR is often expressed as photosynthetic photon flux (PPF): 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 700 nm (total number of photons from 400 to 700 nm). While Einsteins and micromoles are equal (one Einstein = one mole of photons), the Einstein is not an SI unit, so expressing PPF as µmol m-2 s-1 is preferred.

Sensors that measure PPF 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.

Typical applications of quantum sensors include incoming PPF measurement over plant canopies in outdoor environments or in greenhouses and growth chambers, and reflected or under – canopy (transmitted) PPF measurement in the same environments.

Apogee Instruments SQ series quantum sensors consist of a cast acrylic diffuser (filter), photodiode, and signal processing circuitry mounted in an anodised aluminium housing, and a cable to connect the sensor to a measurement device. Sensors are potted solid with no internal air space, and are designed for continuous PPF measurement in indoor or outdoor environments. SQ series sensors output an analogue voltage that is directly proportional to PPF under sunlight (e.g. model SQ-110) or electric lights (e.g. model SQ-120). The voltage signal from the sensor is directly proportional to radiation incident on a planar surface (does not have to be horizontal), where the radiation emanates from all angles of a hemisphere.