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Level Sensors

Troubleshooting

Diagnosing and resolving common issues with HPzenAi LS-PRE level sensors — readings, connectivity, wiring, and installation.

Sensor Not Appearing in the App​

Cause: The gateway cannot detect the sensor — most commonly caused by reversed RS485 A/B wiring or missing 12V power to the sensor.

How to Fix​

  • Verify RS485 A and B wires are not swapped at the gateway terminal block — reversed polarity is the most common cause.
  • Confirm the sensor has 12V DC power by measuring voltage at the sensor power terminals with a multimeter.
  • Check that the sensor RS485 Modbus address is unique on the bus (factory default is typically 1).
  • Run a manual RS485 scan from the app: Gateway → RS485 Scan, and wait up to 60 seconds for results.
  • Inspect the cable for damage, cuts, or water ingress at the connector or junction box.

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Sensor Reading Zero Despite Water in Tank​

Cause: The sensor pressure port is blocked by sediment, the sensor is not fully submerged, or the RS485 connection is intermittent causing stale zero readings.

How to Fix​

  • Confirm the sensor body is fully submerged — a partially or non-submerged pressure sensor reads zero.
  • Lift the sensor slightly and check if the pressure port at the sensor tip is clogged with sediment or debris.
  • Rinse the sensor tip gently under clean water to clear any blockage.
  • Check RS485 terminal connections at the gateway — a loose wire causes intermittent data that may display as zero.
  • Verify the sensor Modbus address has not been reset to 0 — address 0 is reserved and will not respond to gateway polling.

Sensor Reading at Maximum (Full Scale)​

Cause: The sensor range is too small for the actual water depth, the sensor is resting on sediment, or the vent tube is blocked causing incorrect atmospheric compensation.

How to Fix​

  • Confirm the sensor range (2M/4M/6M/8M/10M) is greater than the maximum water depth in the tank — a reading pegged at maximum indicates the water depth exceeds the sensor range.
  • Check if the sensor is resting on the tank floor or buried in sediment — lift the sensor to 50–100 mm above the floor.
  • Inspect the vent tube at the cable exit — blockage causes the sensor to over-read due to incorrect atmospheric pressure compensation.
  • Ensure the vent end of the cable is in open air, dry, and not submerged.
  • If the tank is genuinely at maximum depth and the reading is correct, select a higher-range sensor model.

Erratic or Fluctuating Readings​

Cause: Water turbulence around the sensor, loose cable connections, or electrical interference on the RS485 bus causes reading instability.

How to Fix​

  • Position the sensor away from pump inlets and areas of high water turbulence — mount it in a calm area of the tank.
  • Check all RS485 terminal connections and tighten any loose screws.
  • Ensure the RS485 cable is not routed alongside 230V AC mains cables or motor wiring — separate signal cables by at least 200 mm.
  • Use shielded twisted-pair cable for the RS485 run and connect the shield to earth at the gateway end only.
  • If the cable run is long, install a 120 Ω termination resistor between RS485 A and B at the furthest sensor.

Sensor Shows Negative Reading​

Cause: The sensor is reading below its zero reference — this occurs when the sensor range is mismatched, the vent tube is kinked, or the sensor was calibrated at a different elevation.

How to Fix​

  • Confirm the vent tube is unkinked and unblocked — a partially blocked vent can cause the zero reference to drift negative.
  • Check that the sensor has not been installed inverted or at an elevation higher than the minimum water level.
  • Re-zero the sensor from the app when the tank is at its lowest expected level: Device → Settings → Calibration → Set Zero Point.
  • If the reading is consistently slightly negative (less than −0.1 m), recalibrate the sensor offset via the app calibration tool.

Sensor Offline After Power Interruption​

Cause: The sensor does not reconnect to the gateway because the RS485 address or power supply was not restored correctly after the power outage.

How to Fix​

  • Verify the 12V DC supply to the sensor has been restored and is within 11.5–13.5 V.
  • Wait up to 5 minutes after power is restored — the gateway re-polls all RS485 devices automatically.
  • If the sensor remains offline after 5 minutes, run a manual RS485 scan from the app.
  • The gateway buffers readings during connectivity outages and uploads them to the cloud once reconnected — check historical data in the app for any gap periods.
  • Inspect the RS485 cable for damage that may have occurred during the power event (e.g. from a power surge or nearby lightning strike).

Water Ingress into the Sensor Connector or Junction Box​

Cause: Condensation or direct water entry into the cable connector or junction box corrodes the RS485 terminals and disrupts communication.

How to Fix​

  • Inspect the cable gland where the sensor cable exits the tank — retighten or replace if sealing is compromised.
  • Check the junction box (if used for cable extension) for water inside — dry out and re-seal with weatherproof enclosure sealant.
  • Form a proper drip loop in the cable before it enters the junction box or gateway enclosure to divert water away from the connection.
  • Apply self-amalgamating tape over any exposed connector or splice area that may be exposed to moisture.
  • If terminal corrosion is severe, replace the corroded terminal block and re-terminate the cable ends.

Address Conflict — Multiple Sensors Not Detected​

Cause: Two or more sensors on the same RS485 bus have the same Modbus address, causing data collisions that prevent all affected sensors from being detected.

How to Fix​

  • Disconnect all sensors except one from the RS485 bus and scan — verify the single sensor is detected.
  • Note the address of the detected sensor, then disconnect it and reconnect the next sensor, scanning individually.
  • Set a unique Modbus address (1–32) on each sensor individually before connecting them to the shared bus.
  • Refer to the sensor address configuration section in the quick-start guide — address changes are made via a configuration tool or app command.
  • Once all sensors have unique addresses, reconnect them to the bus and run a full RS485 scan from the gateway.

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Sensor Reading Not Matching Known Tank Level​

Cause: The sensor needs calibration, the tank height parameter in the app is incorrect, or the sensor range model does not match the tank depth.

How to Fix​

  • Open the device tile in the app and go to Settings — confirm the tank height is correctly configured (the maximum water depth the tank can hold).
  • When the tank is at a known level (e.g. empty or full), use the app calibration tool to set the reference point: Device → Settings → Calibration.
  • Confirm the sensor model range (LS-PRE-2M/4M/6M/8M/10M) is appropriate for the tank — the sensor accuracy is rated to ± 0.5% of full scale.
  • Check that the sensor is at the very bottom of the tank — any gap between the sensor and the tank floor reduces the measured water column.
  • Inspect for sediment buildup above the sensor body that may reduce the effective water column being sensed.