Submersible Sensor Installation Guide

Use this guide when the tank uses a submerged pressure/level sensor, such as an HDL300-style sensor, instead of a top-mounted ultrasonic sensor.

Important difference
An ultrasonic sensor measures the empty air distance from the sensor down to the fluid surface. A submersible sensor measures fluid level/depth from pressure while it is under the fluid. Because of this, submersible setup uses the tank overflow/full height as the sensor reference height.

Before You Start

• Create the Monitoring Device in the portal.
• Create or link the Main Tank first.
• If the site has a reserve tank, add the Reserve Tank after the Main Tank is created.
• Know whether the submersible sensor is being used on the Main Tank, Reserve Tank, or both.
• Confirm the tank shape and inside dimensions before installing the sensor.

Portal Setup

1. Open the tank setup form for the correct tank. Main Tank is Sensor A. Reserve Tank is Sensor B.
2. Choose the correct tank shape: Square / Rectangle, Vertical Cylinder, or Horizontal Cylinder.
3. Choose Submersible level sensor as the sensor type.
4. Enter the tank dimensions normally.
5. Enter O / High Water Overflow as the highest usable fluid level. If there is no overflow, use the full usable tank height.
6. Do not enter a separate sensor height for submersible setup. The system automatically treats Sensor Height as equal to High Water Overflow.
7. Enter F / Foot valve to floor only if you want the system to calculate usable fluid below the pickup point.

Physical Installation

• Lower the submersible sensor into the tank so the sensing end is near the bottom reference point used for level measurement.
• Keep the sensor off heavy sludge, sand, or debris where possible.
• Secure the cable so the sensor cannot swing into the wall, pump, inlet, ladder, or other obstruction.
• Route the cable cleanly and protect it from sharp edges, strain, and pump wiring.
• For vented pressure sensors, keep the vent/reference end dry and protected. Moisture in the vent path can cause unstable readings.
• Do not coil excess cable tightly at the wet end of the tank. Secure extra cable in a dry, serviceable location.

RS485 / Service Setup

• Connect the sensor to the Pebble RS485 service bus according to the supplied wiring label and the Pebble RS485 guide.
• Use the Pebble sensor setup/service page to confirm communication with the sensor.
• Confirm the Modbus address, baud rate, and live level reading before leaving the site.
• If multiple RS485 devices are on the bus, each device must have a unique address.

Testing

1. Power up the Pebble Unit and connect it to the site network.
2. Open Sensor Setup and verify the live reading changes in the correct direction as the fluid level changes.
3. Check the tank status page after the first report. The value should behave as a fluid level, not as a top-down air gap.
4. If the value is inverted or out of range, confirm the sensor type, high water overflow value, wiring, and sensor range.

Common Mistakes

• Do not use the ultrasonic sensor height rule for a submersible sensor.
• Do not mount a pressure sensor in air above the fluid. It must be submerged to read level.
• Do not leave the tank set as Ultrasonic if the installed sensor is submersible.
• Do not reuse the same RS485 address on two devices on the same bus.
• Do not confuse Main Tank and Reserve Tank. Sensor A is Main. Sensor B is Reserve.