Reading the Root Zone with the Growlink TerraLINK Substrate Sensor
The Growlink TerraLINK Substrate Sensor reads volumetric water content, bulk EC, and root-zone temperature directly inside coco or rockwool. The probe runs as a TDR substrate probe — Time Domain Reflectometry — so EC drift doesn't corrupt the VWC number during aggressive drybacks. VWC reads 0.0–1.0 m³/m³ at ±0.02 from 0–53% and ±0.04 above. Bulk EC spans 0–20,000 µS/cm at ±(5% + 10 µS/cm) up to 10,000 µS/cm. Temperature lands inside ±0.3 °C across the active grow range. Output is SDI-12 V1.3 on a 30 ft (9 m) pre-terminated cable, with stainless steel rod sealed in IP68 epoxy.
Wiring the TerraLINK Substrate Probe Direct to the PIC
This is the PIC-cable variant. The conductors land directly on the Precision Irrigation Controller's screw terminal block, no M8 connector required. Placement is what makes or breaks the read. In rockwool blocks and slabs, slide the rod in 1 inch from the bottom, equidistant between two plants. In 1-gallon coco pots aim for 2 inches up from the bottom. In 2-gallon and larger, 3 inches. If the 30 ft factory cable doesn't reach, splice with 18 AWG 3-conductor cable for the extension. Keep the total run under 175 ft from probe to controller. Growers running Crop Steering Copilot pair this TerraLINK substrate probe with the controller's irrigation logic for shot-by-shot dryback targeting. Avoid mediums mixed with perlite or expanded clay. Air pockets confuse the waveform. Recalibrate the medium profile in Growlink OS when switching between rockwool, coco, and peat blends.
Key Features
- True TDR Substrate Read: Time Domain Reflectometry keeps the VWC number honest even at high bulk EC and aggressive dryback.
- VWC ±0.02 Accuracy (0–53%): Tight enough to dial in crop-steering shot volumes through veg, transition, and stretch.
- Bulk EC 0–20,000 µS/cm: Reads the full feed range — ±(5% + 10 µS/cm) up to 10,000 µS/cm, ±8% above.
- 30 ft (9 m) Pre-Terminated Cable: Wires straight to the Precision Irrigation Controller's screw terminal block — no M8, no adapter.
- Extendable to 175 ft Total Run: Splice with 18 AWG 3-conductor cable for longer reach to far-corner tents and benches.
Technical Specifications
| Specification | Value |
|---|---|
| Technology | Time Domain Reflectometry (TDR) |
| VWC Range / Accuracy | 0.0–1.0 m³/m³ — ±0.02 (0–53%), ±0.04 (53–100%) |
| Bulk EC Range / Accuracy | 0–20,000 µS/cm — ±(5% + 10 µS/cm) to 10,000; ±8% above; 1 µS/cm resolution |
| Temperature Range / Accuracy | -40 to 85 °C — ±0.4 °C (-40 to 0), ±0.3 °C (0 to 85); 0.10 °C resolution |
| Output Interface | SDI-12 V1.3 |
| Power Supply | 3.6–16 VDC |
| Cable | 30 ft (9 m), pre-terminated — no M8 connector |
| Maximum Total Run | 175 ft (factory cable + 18 AWG 3-conductor splice) |
| Build | Stainless steel rod, epoxy resin seal, IP68 |
| Compatible Host | Growlink Precision Irrigation Controller (PIC) |
| Media Compatibility | Rockwool, coco coir, peat blends (avoid perlite/clay-pebble mixes) |