Technical Note — Decagon VP-4 Temperature, Humidity and Pressure Sensor

Larry Pitts

Created: ; updated: .

The Decagon VP-4 is a microclimate sensor. 

The VP-4 sensor can be used in microclimate and evapotranspiration studies. As part of the Observant Global system, the device can monitor:

  • air temperature
  • relative humidity
  • barometric pressure
  • vapor pressure 

Connection to Field Unit Ports

For a C3 unit, the sensor's bare wires can be connected to the RS232/SDI port directly:

Port Terminal Sensor Wire Colour Alternate Sensor Wire Colour
Power   White Brown
 Tx  Not connected Not connected
 Rx  Red Orange
 Ground  Ground (Bare) Ground (Bare)


For a Solo, the Solo Sensor Accessory Pack (Item #10124) is needed. 

Please refer to the C3 User Guide or Solo User Guide for further cable routing options and information. 


The VP-4 can be mounted to the same pole as the field unit. Cabling can be routed internally or externally. If external routing is preferred, ensure all cabling is contained within suitable UV stable conduit and secured to the pole and VP-4. A drain hole may be added to the lowest point of the conduit if there is a chance of moisture ingress. Please refer to the C3 or Solo User Guides for further cable routing options and information. 

The VP-4 is housed in a solar radiation shield to prevent the possibility of sunlight on the sensor causing false readings of elevated temperatures. The radiation shield is most effective when located where there is adequate ventilation.

Contact Observant if you wish to connect more than one such sensor to a single field unit.


The EnviroPro Soil Probe device should be added via Manage Equipment with the following configuration: 


Manuals, Links and Downloads

Manufacturer's Product Page

Decagon VP-4 product page


The Tech Notes, OBS-USR-TN012-R1-LTR and OBS-USR-TN012-R1-A4, Decagon VP-4 Temperature, Humidity and Pressure Sensor, are available for printing and downloading.

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