1
RS485 Terminal Identification
Locate the RS485 terminals on the AGRI-SOIL-8F junction box — marked A and B (sometimes A+/B− or D+/D−). Terminal A is the positive differential line; terminal B is the negative. Swapping A and B is the most common wiring error and prevents communication entirely. The junction box also has separate 12V+ and GND terminals for power.
2
Single Sensor Wiring
- 1Run shielded twisted-pair cable from the sensor junction box to the HPzenAi Gateway.
- 2Connect: Gateway RS485 A → Junction Box RS485 A.
- 3Connect: Gateway RS485 B → Junction Box RS485 B.
- 4Connect: Gateway 12V output + → Junction Box 12V+.
- 5Connect: Gateway GND → Junction Box GND.
- 6Connect the cable shield to earth at the gateway end only — do not earth the junction box end.
3
Multiple Sensors on One Bus
- 1Daisy-chain all junction box A terminals together and all B terminals together — run the bus from the gateway to each sensor in sequence.
- 2Do not use a star topology — all sensors must be on a single linear bus.
- 3Each sensor must have a unique Modbus RS485 address (1–32) — configure via the sensor address switch or HPzenAi app configuration tool.
- 4Fit a 120 Ω termination resistor between A and B at the junction box of the furthest sensor on the bus.
- 5Maximum cable run: 1000 m at 9600 baud for reliable field communication.
4
Cable Specification
- 1Use 2-core shielded twisted-pair (STP) RS485 cable — Belden 9842 or equivalent outdoor-rated cable.
- 2Minimum conductor size: 0.5 mm² (20 AWG) for field runs — the larger size handles voltage drop over long distances.
- 3Use UV-resistant, direct-burial rated cable for permanently buried field runs.
- 4Route sensor cables in buried conduit or armoured duct to protect from cultivation machinery and rodents.
- 5Maintain at least 200 mm separation from high-voltage irrigation pump cables to prevent interference.
5
Powering the Soil Sensor
RS485 carries communication only — it does not supply power. Each AGRI-SOIL-8F sensor requires 12V DC at the junction box. For short runs, power can be supplied from the gateway's 12V output. For longer runs, use a separate DIN rail power adapter in the field enclosure to avoid voltage drop. Measure voltage at the junction box to confirm it is between 11V and 14V DC.
6
Connector & Weatherproofing
- 1The 7-pin waterproof sensor connector must be fully locked — align the keyway, push in, and rotate until it clicks.
- 2Inspect the connector O-ring before each installation — replace if it shows cracking or compression set.
- 3Apply dielectric grease to the O-ring for installations in very wet or submersible conditions.
- 4Ensure all cable gland entries on the junction box are tightened and rated for the cable diameter.
- 5Seal any unused junction box entries with blanking plugs to maintain the IP65 enclosure rating.
7
Modbus Address Configuration
- 1Factory default Modbus address is 1 — suitable for a single sensor on the bus.
- 2For multiple sensors, assign a unique address to each before connecting to the shared bus.
- 3Address configuration is done via the sensor rotary address switch on the junction box PCB.
- 4In the HPzenAi app, the RS485 Scan automatically detects addresses — no manual address entry is needed in the app.