-68-
v7.2
Sensors probes
4.11.1.
Specifications
General specifications
•
Operating temperature: -40 to 60 ºC
•
Dielectric measurement frequency: 70 MHz
•
Measurement time: 150 ms
•
Dimensions: 10 cm x 3.2 cm x 0.7 cm
•
Prong length: 5.2 cm
•
Cable length: 5 m
Volumetric water content
•
Range: Apparent dielectric permittivity (ε
a
): 1 (air) to 80 (water)
•
Resolution:
-
0.1 ε
a
(unitless) from 1 to 20,
-
< 0.75 ε
a
(unitless) from 20 to 80
-
0.0008 m
3
/ m
3
(0.08% VWC) from 0 to 50% VWC
•
Accuracy: ε
a
: ±1 εa (unitless) from 1 to 40 (soil range), ±15% from 40 to 80 (VWC)
Temperature
•
Range: −40 to 60 ºC
•
Resolution: 0.1 ºC
•
Accuracy: ±1 ºC
4.11.2. Measurement process
The 5TM sensor provides a digital signal using the SDI-12 protocol.
Reading code:
{
// 1. Declare an object for the sensor
Decagon_5TM mySensor(XTR_SOCKET_A);
// 2. Turn ON the sensor
mySensor.ON();
// 3. Read the sensor. Values stored in class variables
// Check complete code example for details
mySensor.read();
// 4. Turn off the sensor
mySensor.OFF();
}
Volumetric water content (VWC) calculation
The 5TM sensor provides the dielectric permittivity (εa) of the surrounding medium. The dielectric permittivity
value must be converted in your code to your particular substrate volumetric water content by a calibration
equation specific to the media you are working in.
The calibration equation for mineral soil (Topp equation) is: