WF8002 Inductive Sensing Design Guide: PCB Sensing Structure, Conductive Metal Target and Mechanical Integration for Water & Gas Meter OEMs

WF8002-based metering solutions for smart water and gas meter applications.

1. How Does WF8002 Detect Mechanical Rotation?

In a compatible meter design, WF8002 works with a PCB inductive sensing structure to detect a conductive metal target moving with the mechanical metering mechanism.

As the conductive target enters, leaves or changes its overlap with the sensing area, the electrical characteristics of the PCB sensing structure change.

WF8002 detects and processes these changes, converting mechanical movement into pulse or digital metering information that can be used by the upper-level system.

Example of a WF8002-based sensing module integrated into a mechanical water meter. Final mechanical integration depends on the target meter design.

For a more complete explanation of the underlying inductive metering principle, see: Smart Water Meter Sensor Working Principle & Inductive Sensing Guide .

2. Why Must the Sensing Structure Be Designed Together with the Customer's Meter Mechanism?

In real OEM projects, WF8002 does not interact with one standardized mechanical target.

Different meter platforms may have significant differences in:

• rotor diameter;
• rotation center;
• target mounting method;
• available PCB space;
• mechanical height and structural tolerance;
• minimum and maximum operating speed.

Example WF8002 sensing PCB and conductive target mechanical relationship. The illustrated geometry and spacing are project-specific and should not be interpreted as universal WF8002 specifications.

For this reason, sensing-structure development should not be based on one fixed PCB geometry or one fixed mechanical distance.

To protect Weifeng's core technology and engineering know-how, this public guide does not disclose proprietary PCB coil routing, sensing-circuit parameters or detailed circuit implementation.

3. The Conductive Metal Target Does Not Have One Fixed Shape

A common misunderstanding is that WF8002 inductive metering requires one fixed metal target geometry.

In practice, the conductive metal target can be customized according to the customer's mechanical meter structure.

Examples of different conductive metal target geometries. Final target design depends on the customer's meter mechanism and project requirements.

Different projects may use:

• semi-circular conductive areas;
• sector-shaped targets;
• partial metal coverage;
• ring-shaped targets;
• custom irregular geometries;
• targets integrated with an existing pointer, rotor or mechanical element.

The final target design should consider:

• the customer's existing rotor structure;
• available installation space;
• target movement path;
• direction-detection requirements;
• PCB sensing-area arrangement;
• machining and assembly tolerance.

4. Sensing Distance Is Project-Specific, Not a Fixed WF8002 Value

The relative distance between the PCB sensing structure and the conductive metal target is an important mechanical parameter affecting detection stability.

However, this distance cannot be defined independently of the actual meter mechanism.

A dimension shown in an engineering illustration represents the mechanical relationship of that particular design example. It should not be interpreted as a universal sensing distance for all WF8002 solutions.

The practical sensing distance can depend on:

• the internal meter structure;
• conductive metal target geometry;
• PCB sensing structure;
• rotation path;
• available installation space;
• mechanical variation;
• required design margin.

5. Why Must Mechanical Tolerance Be Validated During the Prototype Stage?

A laboratory prototype working correctly does not guarantee that every mass-produced meter will behave identically.

The animation below shows the two tolerance checks used on the production line: radial eccentricity up to 0.50 mm while signal intensity holds at 60, and the allowed signal-intensity window of 30-300 with the coil centred.

Production can introduce multiple tolerance sources at the same time:

• shaft eccentricity;
• target-position variation;
• PCB installation-height variation;
• plastic-structure dimensional tolerance;
• component machining tolerance;
• long-term mechanical change or wear.

OEM validation should therefore include more than the nominal position. It should cover the realistic boundary conditions expected in production.

6. Why Should Low-Speed and High-Speed Conditions Be Validated Separately?

Mechanical operating speed can vary significantly depending on meter type, flow rate and application environment.

Low-speed validation should focus on:

• stable detection at very low flow;
• avoiding missed counts when the target moves slowly through the sensing area;
• correct behavior during stop and restart conditions.

High-speed validation should focus on:

• avoiding missed counts during continuous high-speed rotation;
• ensuring the signal response is sufficient for the required metering rate;
• maintaining stable forward/reverse recognition.

Residential, commercial and industrial meters may require different validation conditions, so one fixed test speed should not be used to represent every meter application.

For additional discussion of WF8002 low-power metering design, see: WF8002 Ultra-Low-Power Metering Design .

7. How Can WF8002 Support Forward and Reverse Movement Detection?

When the PCB sensing structure and conductive metal target produce direction-dependent signal changes, a WF8002-based design can support forward and reverse movement recognition.

Engineering validation should cover:

• forward movement;
• reverse movement;
• low-speed reverse movement;
• stop and restart conditions;
• target positions near the sensing boundary;
• mechanical vibration and direction changes.

WF8002 bidirectional pulse metering concept showing the relationship between sensing structure and forward/reverse pulse output.

Explore a WF8002-based bidirectional metering solution: WF8002 Bidirectional Metering Solution .

8. What Information Should an OEM Provide for a New Project?

To improve the efficiency of initial engineering evaluation, meter OEMs should provide as much mechanical and application information as possible.

9. Recommended WF8002 OEM Engineering Validation Workflow

A reliable production design should begin with the customer's real mechanical meter structure, not with a single IC or one ideal laboratory condition.

Mechanical Review -> Target Concept -> Sensing Structure Design -> Prototype -> Distance & Tolerance Test -> Low / High Speed Test -> Forward / Reverse Validation -> Environmental Test -> Production Validation

Testing one sample, one sensing distance or one speed is not sufficient to represent long-term stability under mass-production conditions.

For additional discussion of environmental reliability, see: WF8002 Smart Meter Reliability Design for Harsh Environments .

10. What Can Weifeng Support for Meter OEMs?

Hangzhou Weifeng supports smart water and gas meter manufacturers with WF8002 Metering MCU SoC and related metering solutions.

Typical project support includes:

• WF8002 Metering MCU SoC;
• WF8002-based non-magnetic inductive sensing solutions;
• standard pulse-output sensor PCBAs;
• initial review of customer mechanical structures;
• conductive metal target adaptation recommendations;
• sensing-structure matching support;
• forward / reverse detection solutions;
• OC / TTL output configuration;
• sample validation and project optimization;
• integration with M-Bus, RS485, Wireless M-Bus, LoRaWAN and NB-IoT communication architectures.

To protect Weifeng's core technology and customer project intellectual property, proprietary PCB sensing circuits, detailed circuit parameters and selected design details are discussed only as needed during specific OEM project cooperation.

Related Technical Resources

Frequently Asked Questions

Conclusion: There Is No Universal Dimension, Only a Properly Validated System Design

WF8002-based inductive metering is not simply a combination of one IC, one fixed metal plate and one fixed sensing distance.

Different customer water and gas meters have different mechanical structures. The conductive metal target, sensing structure, mechanical distance and tolerance conditions should therefore be adapted to the specific project.

For meter OEMs, the real engineering objective is to establish a validation system covering Mechanical Structure, Sensing Structure, Tolerance, Speed and Production Variation.