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

SP-212 0-2.5 Volt Pyranometer

The SP-212 is an amplified sensor with a 0-2.5 volt output and exhibits excellent cosine response. All Apogee pyranometers incorporate a silicon-cell photodiode that measures total shortwave radiation with a sensor housing design that features a fully potted, domed-shaped head making the sensor fully weatherproof and self-cleaning. Total shortwave radiation is an important component in determining evapo-transpiration rates, energy balance, net radiation as well as monitoring solar power panels.

Sensitivity: 2.0 mV per W m-2
Calibration Factor: 0.5 W m-2 per mV (reciprocal of sensitivity)
Calibration Uncertainty: ± 5%
Measurement Repeatability: < 1%
Non-stability (Long-term Drift): < 2% per year
Non-linearity: < 1% (up to 1250 W m-2; maximum radiation measurement is 1250 W m-2)
Response Time: < 1 ms
Field of View: 180°
Spectral Range: 380 nm to 1120 nm (wavelengths where response is 10% of maximum)
Directional (Cosine) Response: ± 1% at 45° zenith angle
± 5% at 75° zenith angle
Temperature Response: -0.04 ± 0.04% per °C
Operating Environment: -40 to 60°C, 0 to 100% relative humidity
Dimensions: 2.4 cm diameter and 2.8 cm height
Mass: 70g (with 5m of lead wire)
Power Supply: 5-24 VDC with a nominal current draw of 300 µA
Warranty: 4 years

Solar radiation at Earth’s surface is typically defined as total radiation across a wavelength range of 280 to 4000 nm (shortwave radiation). Total solar radiation, direct beam and diffuse, incident on a horizontal surface is defined as global shortwave radiation, or shortwave irradiance (incident radiant flux), and is expressed in Watts per square meter (Wm-2, equal to Joules per second per square meter). Pyranometers are sensors that measure global shortwave radiation.

Apogee SP series pyranometers are silicon-cell pyranometers, and are only sensitive to a portion of the solar spectrum, approximately 350 – 1100 nm (approximately 80 % of total shortwave radiation is within this range). However, silicon-cell pyranometers are calibrated to estimate total shortwave radiation across the entire solar spectrum. Silicon-cell pyranometer specifications compare favourably to specifications for World Meteorological Organization (WMO) moderate and good quality classifications and specifications for International Organisation of Standardisation (ISO) second class and first class classifications, but because of limited spectral sensitivity, they do not meet the spectral specification necessary for WMO or ISO certification.

Typical applications of silicon-cell pyranometers include incoming shortwave radiation measurement in agricultural, ecological, and hydrological weather networks, and solar panel arrays.

Apogee Instruments SP series pyranometers 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 total shortwave radiation measurement on a planar surface in outdoor environments. SP series sensors output an analogue voltage that is directly proportional to total shortwave radiation from the sun. 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.

Apogee offer these amplified versions of Pyranometers to allow for easy integration into systems that cannot measure small millivolt signals. There are two options: 2.5V and 5V. The voltage listed is the maximum output at the maximum light for which the sensor is calibrated. It is also the minimum input voltage required to power the sensor. For example: the SP-215 has an output of 5V when the solar radiation is at its maximum of 1250 W/m2. If the voltage supplied was only 4V the maximum output would be 4V which means that the sensor would output the same for any light level over 1000 W/m2. This is something to watch for if you are supplying the voltage with batteries.

These sensors have been designed to have all the circuitry inside the head, the same as Apogee’s non-amplified sensors. This means they are rugged and there is no worry about water damage to the circuit board. The circuitry is a basic non-inverting configuration of an operational amplifier (op-amp). The op-amp has been specifically chosen to have a low voltage offset and be physically small enough to fit inside of the current sensor body head. The op-amp has a max voltage specified at 5V which is why the maximum output of our amplified sensors is 5V. Included in the circuitry is a Zener diode that will short to ground if a voltage higher than 6V is applied. This keeps the main circuitry from getting destroyed if the sensor is wired incorrectly.