Sensor And Probe FAQs
Your questions answered about Sentek’s moisture, salinity and temperature sensors.
Sentek sensors measure soil moisture content by emitting an electric field from each sensor in the soil. The frequency of this electric field changes in response to the soil’s dielectric properties providing measurements that are calibrated into volumetric water content.
Each sensor can be programmed with the Sentek default calibration or a user defined calibration. Our sensors can be used on a wide range of soil types and applications.
The raw data each probe measures is converted via a calibration equation into volumetric soil water content. This is reported as the volume of water per unit bulk volume of soil:
1 millimetre = 1 millimetre height per square meter soil area = 1 litre.
If one sensor reads 1 millimetre, that means there is 1 millimetre of water content in a 100 millimetre thick soil slice on a volume basis. For that layer only, this equals a volumetric soil water content of 1 per cent.
Our probes are configured to operate at temperatures between -30°C and 85°C. While measuring frozen soil is possible, the dielectric properties of ice are significantly lower than water. This means measuring permafrost will yield lower soil moisture content readings.
There are several reasons why water can enter an access tube. It may be because the tube is cracked or because the seal in the bottom stopper or top cap is broken or damaged. Use a water bailer to remove pooled water from inside an access tube and follow up with a clean rag, attached to a pole, to dry the inside of the tube. Clean the tube with another rag soaked in methylated spirits before reinserting the probe.
Soil water sensor depths are generally determined by the root zone depth, soil profile and water table. For growing vegetable crops, for example, we typically recommend a 60 centimetre probe length and 90 to 120 centimetres for trees and vines.
The EnviroSCAN probe allows for the adjustment of sensor locations, while the Drill & Drop sensors are fixed in place within the sealed probe.
In commercial operations, we recommend our factory default calibrations for sensors measuring relative changes in soil water dynamics.In situations where absolute volumetric soil water content information is required, it is essential to program each probe sensor with a soil specific, calibration. Read our calibration manual for more information about Sentek probe calibration.
A failed scan commonly occurs when the probe length is shorter than the depth of the profile. To fix this, verify that the soil profile is correct and ensure the full depth of the profile is being reached during the scan. If problem persists, check the condition of the probe cap or the cable connector for damage.
We recommend changing your silica gel bags annually depending on environmental conditions or, alternatively, as soon as the crystals inside the bags turn pink. A change in the colour of the crystals means the bag cannot absorb any more moisture and components of your equipment are at risk of being damaged.
Each probe is fitted with multiple sensors located at a range of depths. These sensors can be customized and changed as needed. The probe rod comes in different lengths to suit a range of crops and monitoring situations.
The sensors utilize electrical capacitance to measure soil moisture. The changing ratio of air and water at each soil depth can be measured very quickly and accurately. Readings are converted to soil moisture measurements using a calibration equation that takes the varying soil types into account.
A cable connects the solar, or battery powered, logging system to the probes at each monitoring site. You can set your system to record data at regular intervals. Data can be downloaded or uploaded to the cloud and viewed on a computer or mobile phone.
Use the matching Sentek auger (e.g. pair a 30 centimetre auger with a 30 centimetre probe) and the installation tripod to make a tapered pilot hole that fits the exact shape of the probe. By following this recommended installation technique, you can insert the probe quickly and easily without disturbing the soil profile. No slurry required!. Watch our video here.