Sensorscope: Technology

Sensors

Sensorscope stations includes a sensor interface board accommodating seven external sensors, which makes the station capable of measuring nine different data inputs: ambient temperature and humidity, infrared surface temperature, solar radiation, wind speed and direction, precipitation, soil moisture, and soil pressure. The system has been tested with external multiplexers which allow for multi-sensor configurations for each parameter. This page presents each sensor specifications and callibration procedure.

 

Air Temperature and Humidity

Sensor and Vendor:

  • SHT75, Sensirion [1]

Measurement Type:

  • Temperature Digital (14 bits)
  • Humidity Digital (12 bits)

Unit:

  • Temperature: °C
  • Humidity: % (relative humidity)

Range:

  • Temperature: -20 – 60
  • Humidity: 0 – 100

Accuracy:

  • Temperatue: ± 0.3°C
  • Humidity: ±2%

Conversion Formula:

  • Temperature: T = -39.6 + 0.01 * rawValue
  • Humidity: Rh = (temperature (in °C) – 25.0) * (0.01 + 0.00008 * rawValue) + RHlin, where Rhlin = -4.0 + 0.0405 * rawValue – 2.8 * 10^-6 * rawValue^2

where rawValue is the 14/12 bits value provided by the sensor

Additional info:

  • Sensirion SHT7x and SHT1x: Specifications [2]
  • Filter for SHT1x: Specifications [3]

 

Infrared Surface Temperature

Sensor and Vendor:

  • TN901, Zytemp [4]

Measurement Type:

  • Digital sensor: 16 bits

Unit:

  • °C

Range:

  • -20 – 70

Accuracy:

  • ±0.6°C

Conversion Formula:

  • Tir = (rawValue / 16.0) – 273.15,

where rawValue is the 16 bits value provided by the sensor

Additional info:

 

Anemometer

Sensor and Vendor:

  • Davis Anemometer [5]

Measurement Type:

  • Wind Speed: Interrupts. Stations send the number of revolutions in the last measured period (16bits)
  • Wind Direcction: Analog sensor (potentiomenter) (12 bits ADC max: 3.64v)

Unit:

  • Wind Speed: m/sec
  • Wind Direcction: °

Range:

  • Wind Speed: 1 – 10
  • Wind Direcction: 0 – 360

Accuracy:

  • Wind Speed: ±5% (valid only for speeds > 1m/s)
  • Wind Direcction: ±7°

Conversion Formula:

  • Wind Speed: 1600 revolutions per hour for each MPH
  • Wind Direection: Wdir = Vout*360/Valim, where Vout is the voltage read from the sensor (in V), and Valim = 3.3V (vinput to the sensor)

Additional info:

  • Installation Manual [6]
  • Specifications [7]

 

 

Solar Radiation

Sensor and Vendor:

  • Davis solar Radiation [8]

Measurement Type:

  • Analog Sensor (12 bits ADC max: 3.64v)

Unit:

  • W/m2

Range:

  • 0-1500

Accuracy:

  • ±5%

Conversion Formula:

  • 1.67 mV per W/m2

Additional info:

  • Instruction Manual [9]
  • Specifications [10]

 

Pluviometer

Sensor and Vendor:

  • Davis Rain Collector II [11]

Measurement Type:

  • Interrupt: Station sends the cummulative tips since last reboot (8 bits)

Unit:

  • mm

Range:

  • x0.2mm

Accuracy:

  • ±10% (experimentally)

Conversion Formula:

  • one tip = 0.2 mm

Additional info:

  • Instruction Manual [12]
  • Specification Sheets [13]

 

Soil moisture

Sensor and Vendor:

  • ECH20 EC-5 probe, decagon [14]

Measurement Type:

  • Analog value (12 bits ADC max: 2.5v)

Unit:

  • % (relative humidity)

Range:

  • 0-55

Accuracy:

  • ±10%

Conversion Formula:

  • Rh = 1.19 * Vmea – 0.4

where Vmea voltage read from the sensor in V

Additional info:

 

Soil pressure

Sensor and Vendor:

  • Watermark, Irrometer [15]

Measurement Type:

  • Analog (adaptation needed) (12 bits ADC max: 2.5v)

Unit:

  • kPa

Range:

  • -200 – 0

Accuracy:

  • Not data found

Conversion Formula:

  • Interpolated graph

Additional info:

  • SMX Electrical Interface for Watermark™ or Gypsum Block Sensors. [16]
  • Calibration for the watermark 200SS Soil Water Potential Sensor to fit the 7-19-96 “Calibration #3” Table from Irrometer, Rick Allen Univ. of Idaho October 13, 2000. [17]
  • Installation of the watermark. [18]

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