VWC Sensor Setup

The Aranet Soil Sensor WET150 measures root-zone conditions in soil and substrates.

It reports volumetric water content (VWC), temperature, and electrical conductivity (EC). Use these metrics to tune irrigation and nutrient dosing.

WET150 specs: WET150 Datasheet

Data flow is simple:

• WET150 measures in the substrate.

• The Aranet transmitter collects readings wirelessly.

• The Base Station calculates and displays configured metrics.

Working principle

The sensor measures volumetric water content (VWC), not substrate saturation.

• Saturation ranges from 0% (dry) to 100% (runoff starts).

• VWC is the % of substrate volume occupied by water.

The same saturation can produce different VWC values. It depends on substrate type and packing density. For example, perlite can saturate around ~30% VWC.

The sensor uses two electrodes in the substrate. It provides both direct and calculated values:

• Direct: dielectric permittivity (DP), bulk electrical conductivity (ECb), temperature (T)

• Calculated: volumetric water content (VWC), pore electrical conductivity (ECp)

Setting up the sensor

WET150 works in field soils and controlled-environment substrates. This includes rock wool, coir, peat, and perlite mixes.

Installation quality drives measurement quality. Exposed prongs or air gaps will read too dry.

Sensor placement

Proper sensor placement is essential for reliable VWC and EC readings. Most “bad data” problems come from installation.

Install the sensor in the main root zone. Avoid areas that stay saturated, dry out fast, or get exposed.

Choosing the installation location

Choose a representative location for your facility. Avoid areas that distort readings:

• Directly next to irrigation emitters

• Extreme slab ends

• Poorly mixed or uneven substrate

Ensure the prongs are surrounded by uniform, compact medium. Avoid large air pockets around the prongs. Keep placement consistent when comparing trials.

Key positioning principles

Moisture and roots are not uniform. Target the zone that stays moist between irrigations.

1. Container size

   • Place the sensor at 1/4–1/3 of substrate height from the bottom.

   • This avoids surface drying and drainage zones.

2. Substrate density

   • Loose media is sensitive to air gaps.

   • Ensure tight contact around the prongs.

3. Irrigation layout

   • Install a few cm from drippers.

   • Do not install directly underneath a dripper.

4. Crop stage

   • Young plants use shallower water.

   • Mature plants use deeper zones.

5. Avoid extremes

   • Too low → drainage and saturation bias.

   • Too high → surface drying bias.

Recommended installation location in slabs

Install from the side, around the slab’s mid-length. With one sensor, target the middle plant’s root zone. With two sensors, place them between three plants. Figure 3 shows example positions.

If you have one sensor per plant, place each in that plant’s root zone.

Positioning recommendations

Typical horticultural substrates

For slabs ~7.5–10 cm (3–4 in) high:

• Install horizontally, 32 mm (1.25 in) from the bottom.

• This matches Aranet substrate profile calibration conditions.

• On the installation bracket, this is Position 1 (TDAWSH01).

Added rigidity

Recommended installation location in containers and pots

Calibration is done at 32 mm from the bottom. In taller pots, install at the crop’s main uptake zone depth. If you use the installation bracket (TDAWSH01), start with these positions:

Accessory position	Container volume	Approx. height of container	Sensor height
1	1.9 gal / 3.8–7.2 l	7–8 cm / 2.76–3.15 in	32 mm (1.25 in)
2	3.9 gal / 7.6–14.75 l	18–23 cm / 7.09–9.06 in	51 mm (2.0 in)
3	7 gal (Standard) / 15.15–26.5 l	28–30 cm / 11.02–11.81 in	70 mm (2.75 in)
4	7 gal (Tall & Narrow) / 15.15–26.5 l	30–35 cm / 11.81–13.78 in	89 mm (3.5 in)

If possible, compare trends at 51/70/89 mm against 32 mm. This helps you understand vertical water distribution. For pots and blocks, install centrally and away from edges.

Installing the sensor

1

Inserting prongs into the substrate

Start installation after you choose the location.

• Push the prongs in fully. Do not leave any prong area exposed.

• Install from the side when possible. Keep prongs parallel to the substrate base.

• Keep height and position consistent across all samples.

• Do not reinstall into the same holes. Use a nearby fresh spot.

• Keep prongs at least 30 mm from container edges.

• Vertical (top-down) installation is possible. Expect lower VWC readings.

Interaction between multiple sensors

Keep sensors at least 100 mm apart. Measure between both bodies and prongs. This prevents electromagnetic interference and inaccurate readings.

Outdoor installation in soil

For field measurements, bury the whole sensor body in soil. Keep the prongs in undisturbed soil. This improves stability and protects from heat and impact.

Positioning the transmitter

Mount the transmitter body (white housing) above the plant canopy. This improves wireless link quality. If you need extra length, use the WET150 transmitter extension cable.

Taking initial measurements

After installation, run at least one full saturation cycle. Saturate to runoff to remove trapped air.

Resaturate after relocating or reinserting the sensor. This improves accuracy and stability.