Level Sensors

RS485 Wiring

Connecting HPzenAi LS-PRE level sensors to the gateway over an RS485 bus — cable selection, terminal wiring, multi-sensor daisy-chain, and termination.

How RS485 Wiring Works for Level Sensors

HPzenAi LS-PRE level sensors use RS485 Modbus RTU for communication. The sensor cable is a 3-wire vented cable: 12V DC power, RS485 A (positive differential signal), and RS485 B (negative differential signal). The gateway provides the RS485 bus master function, polling each sensor by its Modbus address. Sensors can be connected individually or daisy-chained up to 32 devices on a single RS485 bus port.

RS485 Terminal Identification

Identify the correct terminals on both the sensor cable and the gateway terminal block before wiring. Incorrect polarity on RS485 A/B prevents all communication.

Wire / Terminal	Label	Function
Red or Brown	+12V	12V DC power supply to the sensor
Black	GND	Power supply ground / negative return
Yellow or White	RS485 A	RS485 differential signal — positive
Green or Blue	RS485 B	RS485 differential signal — negative
Shield / Drain	Shield	Cable shield — connect to earth at gateway end only

Cable Selection

Use the correct cable type for reliable RS485 communication over the full sensor cable run.

Steps

• Use shielded twisted-pair (STP) cable with a minimum 0.5 mm² conductor cross-section.
• For runs up to 10 m, the sensor's pre-attached cable is sufficient — no extension needed.
• For runs from 10 m to 100 m, extend using shielded RS485 cable (e.g. Belden 9841 or equivalent).
• Maximum recommended cable run: 100 m for LS-PRE sensors at 9600 baud.
• For longer runs, reduce the bus baud rate to 4800 or 2400 baud in the gateway RS485 settings.
• Do not use unshielded cable (standard twin-and-earth or speaker wire) for RS485 runs in environments with electrical machinery.

Single Sensor Wiring

For a single level sensor connected directly to the gateway, make the following connections at the gateway terminal block.

Visual reference coming soon

Steps

• Sensor +12V wire → Gateway +12V output terminal (or separate 12V PSU positive).
• Sensor GND wire → Gateway GND terminal (or separate 12V PSU negative).
• Sensor RS485 A wire → Gateway RS485 A terminal.
• Sensor RS485 B wire → Gateway RS485 B terminal.
• Connect the cable shield to the gateway earth terminal — leave the far (sensor) end of the shield unconnected.
• Tighten all terminal screws to 0.5–0.6 Nm — overtightening can damage terminal spring contacts.

Multiple Sensors on One Bus (Daisy-Chain)

Up to 32 LS-PRE sensors can share a single RS485 bus on one gateway port. Use a daisy-chain topology — run the bus from the gateway to the first sensor, then on to the second, and so on. Do not use a star topology (individual cables from each sensor back to the gateway).

Visual reference coming soon

Steps

• Run the RS485 bus cable from the gateway terminal block to the first sensor, then on to the second sensor, and continue to the furthest device.
• At each sensor, break out the A, B, and power wires to the sensor's terminals and continue the bus cable to the next sensor.
• All RS485 A terminals are connected together on the shared bus; all RS485 B terminals are connected together.
• Each sensor must be configured with a unique Modbus address (1–32) before connecting to the shared bus.
• Install a 120 Ω termination resistor between RS485 A and B at the terminals of the furthest sensor only.
• Do not install termination resistors at intermediate sensors — only at the end of the bus.

Powering Multiple Sensors

The 12V DC power and RS485 signal are carried in the same cable for LS-PRE sensors. However, the gateway's onboard 12V output has a limited current capacity. For installations with many sensors, use a separate DIN rail 12V power supply.

Steps

• Each LS-PRE sensor draws approximately 50–80 mA at 12V DC during normal operation.
• The gateway's onboard 12V output supports up to 500 mA total — suitable for up to 6 sensors from the gateway supply.
• For 7 or more sensors, use a dedicated DIN rail 12V power supply (rated 2A or higher) for sensor power.
• Connect the power supply negative (GND) to the gateway GND terminal to ensure a common reference for RS485 communication.
• Use an HPzenAi SPD (surge protection device) on the power supply mains input for outdoor or lightning-exposed installations.

RS485 Wiring Checklist

Verify all wiring before powering on and scanning for devices.

Steps

• RS485 A and B wires connected to correct terminals (not swapped).
• All terminal screws tightened firmly.
• Cable shield connected to earth at gateway end only.
• Bus topology is daisy-chain — no star wiring.
• 120 Ω termination resistor installed at the furthest sensor only.
• Each sensor has a unique Modbus address (1–32).
• Total cable run does not exceed 100 m.
• Power supply capacity is sufficient for the number of sensors installed.
• Cable routed away from high-voltage and motor wiring by at least 200 mm.