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 over a 2 m M8 cable, with stainless steel rod sealed in IP68 epoxy.
Placing and Wiring the TerraLINK Substrate Probe for Crop Steering
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. The probe wires into a canopyLINK port via M8 — Pin 1 12V red, Pin 2 signal white, Pin 3 ground bare. It can also run to the Precision Irrigation Controller on the 30 ft (9 m) cable variant. 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 — the 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.
- SDI-12 V1.3 Output: Wires to canopyLINK over M8 or to the Precision Irrigation Controller (PIC) on the 30 ft cable variant.
- IP68, Stainless + Epoxy: Stainless steel rod sealed in epoxy resin holds up in coco runoff, rockwool slurry, and high-salt drainback.
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 / Connector | 2 m cable, M8 connector (canopyLINK); 30 ft / 9 m variant for PIC |
| M8 Pinout | Pin 1 = 12V (Red), Pin 2 = Signal (White), Pin 3 = Ground (Bare) |
| Build | Stainless steel rod, epoxy resin seal, IP68 |
| Compatible Hosts | Growlink canopyLINK, Precision Irrigation Controller (PIC), Crop Steering Copilot |
| Media Compatibility | Rockwool, coco coir, peat blends (avoid perlite/clay-pebble mixes) |