Use a WET150 meter to connect directly to the WET150 sensor and measure the “RAW” soil type setting: Permittivity, ECb and Temperature
Press the SET button on the WET150 meter.
Scroll down to “Soil type”, press SET.
Scroll to “RAW” press SET
Air test:
Hold sensor with rods pointing up in the air.
Press the “Read” button.
Permittivity (ɛ) should = 1 (+/- 0.5)
ECb should = 0 (+/- 1mS.m-1).
Tap water test:
Fill a 1 litre container of tap water.
Insert the WET150 sensor into the middle of the water container, rods facing down into the water. Ensure the rods are covered by the water but not too deep – the water should not reach the side screws in the body of the WET150.
Ensure there is sufficient water around the rods (at least ~2cm from side walls and bottom of container).
*note this is very important! If the rods are too close to the side walls or bottom of the container, the sensing field will breach the container and you’ll be reading air/container material as well as the water. This will reduce the reading significantly.
Press the “read” button on the WET150 meter and note down the temperature and permittivity readings.
Using the temperature reading (in degC), work out what the estimated permittivity should be using: 87.48 – 0.365(T) where T is the temperature in degC:
87.48 – (0.365 x 24.7) = 78.5
WET150 permittivity (ɛ) should be reasonably close to the estimated value worked out using the temperature value above. Note: this is a rough test so the accuracy is not a strict limit.
The results from the temperature calculation above are 78.5 compared to the sensor reading of 79.5.
This is just a check to see if the sensor is in the correct region but, even with the published accuracy of +/-5%, the sensor is responding very closely.
Hanna fluid test:
Obtain a bottle of Hanna conductivity calibration fluid, for example the 1413uS/cm-1 (HI-70031P 1413µS/cm Conductivity Solution, x25 Sachets (hannainstruments.co.uk)
You will need enough fluid to fill a container so that, when the WET150 rods are inserted, they have a sufficient amount of fluid between the rods and the side and bottom of the container (at least ~2cm).
As above, insert the sensor into the middle of the fluid, rods facing down, water level no higher than the screws in the side of the body. Please note warnings about the sensor being too close to the side/bottom of the container – this will significantly reduce the reading.
ECb should match Hanna fluid +/- 5% +/-100uS.cm-1. However, take note of the temperature! The Hanna 1413 fluid specification is at 25degC. If the temperature is different from 25degC, use the look-up table on the side of the bottle to see what the reading will be at different temperatures
For example, at 24degC, the 1413uS/cm-1 solution should be 1386uS.cm-1 but, given the accuracy of the WET150, this means that any reading between 1216 and 1555uS.cm-1 is acceptable. In reality, we would expect it to be closer though:
*Note: pay attention to the units. You can change the units on the WET150 meter so you can read the same units as the Hanna solution (uS.cm-1).