LumeLevel RS485 Sensor Bus v1 — M12 Installation Guide

The Bus v1 standard

The installer works with complete connectors and approved adapters rather than constructing the normal RS485 trunk conductor-by-conductor in the field.

M12 4-pin A-coded All standard trunk, T-distributor, sensor-drop and bus-end connections use the keyed four-contact M12 Sensor Bus interface.

Four conductors only Bus v1 carries protected +12 V field power, 0 V/common, RS485 D−/B and RS485 D+/A. Bus v1 does not add a fifth shield conductor.

Linear trunk Build one continuous trunk from the Pebble through the required T-distributors to the far-end terminator. Do not create a passive star.

Short sensor drops A sensor branch leaves the trunk through the sensor port of a T-distributor. Each M12 sensor drop is limited to 2 m maximum.

100 m maximum trunk The Bus v1 trunk from Pebble to the far-end terminator is limited to 100 m maximum.

Terminate the physical far end The Pebble provides the controller-end 120 Ω termination. Install one removable M12 120 Ω terminator at the final trunk-out port and nowhere else.

Installer objective: A normal Bus v1 installation should be connect, route, secure, terminate, configure and test — not strip, splice and field-terminate the RS485 trunk.

Components the installer will handle

1

Pebble RS485 bus port

The Pebble presents the female M12 Bus v1 connection and forms the controller end of the RS485 trunk.

2

M12 trunk cable

Use approved M12 4-pin A-coded male-to-female trunk extension cables between the Pebble and T-distributors and between successive T-distributors.

3

M12 T-distributor

The T-distributor has a male trunk-in connection, female trunk-out connection and female sensor-branch connection. The trunk passes straight through the T.

4

M12 sensor drop

Use an approved male-to-female M12 drop from the T-distributor sensor port to the sensor or sensor adapter. Maximum drop length is 2 m.

5

Sensor adapter

Where the selected sensor does not itself present the LumeLevel M12 Bus v1 interface, use the approved sensor-specific adapter. The adapter presents a male Bus v1 connection to the drop cable.

6

120 Ω M12 bus-end terminator

The removable male M12 terminator plugs into the unused female trunk-out port of the final T-distributor. It terminates the physical far end of the bus.

Illustration

Illustrated component reference

Illustrative component reference — component appearance may vary by approved supplier.

Supported RS485 ultrasonic sensor · Sensor adapter

Supported RS485 submersible level sensor · Sensor adapter

Illustrations are for component recognition and installation context. Connector pinout and topology diagrams remain authoritative.

Correct physical topology

Use one T-distributor for each standard sensor location. The trunk continues through every T; the sensor leaves the trunk on the short drop.

Pebble

Female M12 bus port · controller-end 120 Ω termination

→

M12 trunk

Male → female

→

T-distributor

Trunk continues · sensor drop branches here

→

Next trunk / T

Repeat only as required by the installation

→

Final T trunk-out

Install male M12 120 Ω bus-end terminator

Correct
Pebble → trunk → T → trunk → T → final M12 terminator, with each sensor connected on a short drop from its T-distributor.

Not Bus v1
One point feeding several long passive branches, a T-distributor installed on another sensor drop, or multiple terminators placed at sensor locations.

M12 4-pin A-coded electrical assignment

This pin assignment is fixed across LumeLevel RS485 Sensor Bus v1 components. Connector keying and the standard conductor colors are used to keep every manufactured cable and adapter consistent.

Pin	Standard color	Bus v1 signal	Function
1	Brown	+12 V	Protected field-power rail
2	White	LL-D− / RS485 B	RS485 negative / B data conductor
3	Blue	LL-0V / GND	Field-power return and common reference
4	Black	LL-D+ / RS485 A	RS485 positive / A data conductor

Bus v1 is four-wire and unshielded. Do not add a fifth shield/drain connection to the standard connector system and do not substitute an RJ45 or Ethernet pin convention.

Model and bus limits

Item	Bus v1 limit
Pebble Eco 2	Maximum 2 supported RS485 nodes
Pebble Plus	Maximum 6 supported RS485 nodes
Trunk length	100 m maximum
Individual sensor drop	2 m maximum
Controller-end termination	120 Ω termination provided by the Pebble RS485 hardware
Far-end termination	One removable male M12 120 Ω terminator at the final trunk-out port

Field installation sequence

Confirm the design before mounting. Identify the Pebble model, sensor count, sensor types, T-distributor locations, drop locations, trunk route, power source and final terminator location.
Confirm the components. Use the correct M12 4-pin A-coded trunk cables, T-distributors, sensor drops, approved sensor adapters and one far-end 120 Ω terminator.
Route before final connection. Keep the cable supported and protected from sharp edges, crushing, repeated movement, standing water where the component is not rated for it, and avoid unnecessary parallel routing beside high-current pump or mains conductors.
Connect with power isolated. Align the A-code key before engagement. Never force or cross-thread the connector. Seat the connector fully and secure the threaded coupling without allowing cable weight to load the connection.
Build the linear trunk. Connect the trunk through each T-distributor in sequence. Connect the sensor on the dedicated short drop port. Do not install another T-distributor on a sensor drop.
Install the far-end terminator. Fit the male M12 120 Ω terminator to the unused female trunk-out port of the final T-distributor.
Power and configure systematically. Where device addressing is required, configure or verify addresses methodically so every active node on the bus has a unique address.
Verify the complete bus. Confirm every required node responds, every configured sensor matches the real installation, readings are plausible, and communication remains stable with the complete intended bus connected.
Secure and document. Complete final cable support and weather protection, then record the sensor/address/tank relationship and any installed sensor adapters for future service.

What not to build on Sensor Bus v1

No RJ45 / Ethernet bus parts Do not use RJ45 patch leads, Ethernet splitters, Ethernet T-connectors or RJ45 terminators as Bus v1 field components.

No improvised trunk junction boxes Do not replace the standard M12 trunk and T-distributors with loose field-spliced trunk conductors in generic junction boxes.

No passive star Do not split one bus point into several long trunk branches.

No T on a sensor drop A sensor drop serves one supported node or one approved sensor adapter. Do not branch it again.

No intermediate terminators Do not add termination at each sensor, adapter or T-distributor. Bus v1 is terminated only at its two physical ends.

No unapproved pinout changes Do not swap A/B, power or ground by modifying a standard trunk cable to make an incompatible sensor work. Use the correct approved sensor adapter.

Sensor adapters and non-M12 sensors

Some supported sensors or interface modules may use their own native pigtail, terminals or connector. That does not change the Sensor Bus v1 trunk.

Boundary rule: The M12 trunk ends at the approved sensor adapter. Any sensor-specific conductor termination belongs on the sensor side of that adapter and must follow the adapter and sensor instructions. Do not expose or splice the Bus v1 trunk to avoid using the approved adapter.

Supported sensor examples

Pebble-A01 RS485 ultrasonic

Mount and aim the sensor for the required measurement geometry. Connect it to Bus v1 using its approved M12 interface or sensor adapter rather than modifying the trunk.

Supported short blind-zone RS485 ultrasonic sensor

Pebble-A02 RS485 ultrasonic

Use where the selected tank geometry requires the supported shorter blind-zone ultrasonic option. Preserve the same M12 Bus v1 topology.

Pebble-300 submersible

Protect the sensor cable and any vent/reference arrangement required by the selected sensor. Use the approved Bus v1 sensor adapter where the sensor does not provide the standard M12 interface.

Bus v1 commissioning check

A bus that communicates once is not automatically a commissioned installation. Confirm the complete physical and configured system.

Pebble model and permitted node count match the installed system.
The trunk is linear and remains within the 100 m Bus v1 limit.
Each sensor is connected from a T-distributor on a drop no longer than 2 m.
No T-distributor has been added to a sensor drop.
The final trunk-out port contains the removable M12 120 Ω terminator.
Every required RS485 node has the correct unique address and supported communication settings.
Every M12 connection is correctly keyed, fully seated, secure and appropriately protected for its installation environment.
Each physical sensor, portal sensor type, tank relationship and live reading agree.
The complete bus remains stable after final cable routing and securing.

Bus v1 troubleshooting order

1. Inspect connectors Check M12 keying, seating, coupling, damaged contacts, damaged cable and the affected sensor adapter.

2. Confirm the terminator Verify that the single removable 120 Ω M12 terminator is installed at the physical far-end trunk-out port.

3. Confirm topology Check for a passive star, an over-length drop, a T installed on a drop, an omitted trunk section or an unintended extra terminator.

4. Confirm node configuration Check the affected node address, sensor type and supported communication settings.

5. Isolate systematically If necessary, reduce the bus to a known-good node and reconnect sections in sequence until the failing component, adapter, drop or node is identified.

6. Check electrical conditions safely Where power or signal measurements are genuinely required, use the approved service method and only perform energized electrical work when competent, authorized and equipped to do so safely.

Do not bypass the connector system during troubleshooting. Cutting open a standard Bus v1 trunk cable, substituting an RJ45 adapter, or temporarily field-splicing the trunk can introduce a second fault and is not an accepted commissioning repair.

Safety and stop-work boundary

Isolate power before altering connectors, replacing damaged bus components, opening an approved sensor adapter for conductor-level work, or performing work that does not require energized operation.
Do not probe energized conductors unless the person performing the work is competent, authorized and using an appropriate safe electrical work method.
Stop and escalate when diagnosis or repair exceeds the installer’s qualification, site authorization, equipment or safe access.
An intermittent bus, damaged M12 connection, missing termination, unresolved power problem, unreliable reading or unexplained communication fault is not a commissioned condition.

Component identification standard

LumeLevel installer material for Sensor Bus v1 should show the hardware an installer actually handles: the Pebble, M12 4-pin A-coded trunk cables, M12 T-distributors, short M12 sensor drops, approved sensor adapters and the removable M12 120 Ω far-end terminator.

Visual exclusion: RJ45 plugs, Ethernet patch cables, Ethernet splitters, generic network terminators and loose-conductor junction-box imagery must not be used to illustrate the standard Bus v1 installation.