The Apogee Guardian is an elegant device that provides accurate measurements of important indoor environmental parameters. The SM-500 is a user-friendly datalogger with multiple integrated sensors to measure PAR, air temperature, humidity, vapor pressure deficit and dewpoint, CO2 concentration, barometric pressure, and daily light integral* and photoperiod* (*only accessible via Bluetooth). Graphical summaries of these measurements can be downloaded to dataloggers via Modbus or smartphones via Bluetooth with the Apogee Connect app (iOS/Android). While the SM-500 can take measurements as a stand-alone device mounted to a mast (AM-270, coming soon) or hung by thin wires, it can also integrate into systems for greenhouses, grow rooms, and vertical farms via Modbus or Bluetooth.

The SM-500 is constructed from high-quality ASA plastic with low thermal conductivity and a gloss white finish in selective areas to lower emissivity. The Guardian is filled with foam to provide additional thermal insulation. The internal airway utilizes a small venturi constriction to maximize airflow efficiency over the thermistor, which minimizes the thermal boundary layer’s influence on temperature measurements. Simultaneously, a separate module used to measure CO2, humidity, and pressure is aspirated by a passive, low velocity airstream using a “fluid entrainment” principle. Additionally, a quantum sensor is mounted on the top of the shield to measure PAR.

The Guardian comes in two model versions: the SM-500 and SM-600. The SM-500 and SM-600 models are identical in all ways (size, function, and appearance) except for the embedded light sensor. The SM-600 sensor measures extended photosynthetically active radiation (ePAR), while the SM-500 measures PAR (400-700 nm). For the ePAR option, please see our SM-600 model.