SQ-421 SDI-12 Digital Output Quantum Sensor

The SQ-421 is a digital sensor that uses SDI-12 communication protocol.

  • Product Name: SDI-12 Digital Output Quantum Sensor
  • Item No.:SQ-421
  • Manufacturers:Apogee
  • Country of Origin:USA

The SQ-421 is a digital sensor that uses SDI-12 communication protocol. The sensor is calibrated for sunlight and electric lights, selectable through SDI-12 commands, and has a command that automatically applies the immersion effect correction factor for underwater measurements. The sensor features a rugged, self-cleaning sensor housing design. Typical applications include PPFD (Photosynthetic Photon Flux Density) 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 PAR (Photosynthetically Active Radiation)/PPFD in aquatic environments, including salt water aquariums where corals are grown.


Input Voltage Requirement    4.5 to 24 V DC

Current Drain    0.6 mA (quiescent), 1.3 mA (active)

Calibration Uncertainty    ± 5 %

Measurement Repeatability    Less than 0.5 %

Long-term Drift (Non-stability)    Less than 2 % per year

Non-linearity    Less than 1 % (up to 4000 µmol mˉ² sˉ ¹)

Response Time    0.6 s, time for detector signal to reach 95 % following a step chang, fastest data tranmission rate for SDI-12 circuitry is 1 s

Field of View    180˚

Spectral Range    410 to 655 nm ( wavelengths where response is greater than 50 % fo 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 30 m

Dimensions    44 mm height, 23.5 mm diameter

Mass    177 g (with 5 m cable)

Cable    5 m of two conductor, shielded, twisted-pair wire, additional cable available in multiples of 5 m; TPR jacket (high water resistance, high UV stability, flexibility in cold conditions); pigtail lead wires