Advancing Strain Gage–Based Force and Torque Measurement with FlexCircuits and EMC

1. Introduction

Strain gage–based force and torque sensors have long been the gold standard for precision measurement across industries such as automotive testing, aerospace, industrial automation, and materials research. Despite decades of refinement, one aspect of sensor manufacturing has remained stubbornly complex: wiring.

As highlighted by Yuval Hernik, traditional strain gage sensor assembly relies heavily on manual processes—cutting, stripping, soldering, routing, and balancing lead wires. While functional, these methods introduce variability, increase labor costs, and limit scalability, particularly in high-volume production environments.

This case study examines how the transition from conventional hand-wiring to flex circuit–integrated strain gage assemblies, combined with Effective Modulus Compensation (EMC), is reshaping sensor manufacturing. The approach not only improves consistency and thermal performance but also unlocks new sensor design architectures previously constrained by

wiring limitations.

2. The Traditional Challenge: Wiring as a Hidden Source of Error

In a conventional strain gage-based Wheatstone bridge configuration, precision depends not only on gage placement but also on electrical symmetry. Equal-length lead wires, proper solder joints, and carefully selected adjustment resistors are critical to achieving:

• Bridge balance

• Zero temperature coefficient (TC)

• Span TC compensation

As Yuval points out, achieving these conditions through manual wiring is labor-intensive and error- prone. Even skilled technicians face challenges such as:

• Inconsistent solder joints affecting resistance

• Thermal gradients introduced by uneven lead lengths

• Wiring errors during assembly or rework

• Signal variability between nominally identical sensors

In low-volume prototyping, these challenges are manageable. In scaled manufacturing, however, they become costly—driving rework, calibration time, and scrap rates.

3. Process Innovation: From Hand Wiring to Flex Circuits

The innovation described by Yuval replaces discrete lead wires with flex circuits directly integrated into the strain gage assembly. This shift fundamentally changes how sensors are built.

Key Characteristics of Flex Circuit Integration

• Automated wire bonding replaces hand soldering

• Fixed, repeatable conductor geometry eliminates lead-length variation

• Predefined routing paths remove assembly ambiguity

• Compact form factor improves packaging efficiency

By removing manual wiring steps, manufacturers achieve process consistency by design, not by inspection.

As several industry professionals commented on the original post, reduced soldering alone dramatically improves reliability—since solder joint quality is one of the most common failure points in precision sensors.

4. Manufacturing Efficiency Gains

One of the most immediate benefits of flex circuit integration is labor reduction.

Traditional wiring requires:

• Skilled technicians

• Multiple manual steps

• Visual inspection and electrical verification

• Rework loops for wiring-related defects

Flex circuit–based assemblies eliminate many of these steps entirely.

Additionally, the self-adhesive backing integrated into the flex circuit further streamlines manufacturing. As noted by Yuval, this removes the need for:

• Mixing and storing adhesives

• Managing chemical shelf life

• Waiting for air-dry curing cycles

Instead, the process becomes:

Clean → Clamp → Heat Cure → Done

The result is faster throughput, lower variability, and improved shop-floor ergonomics.

5. Thermal Accuracy Without Electrical Compromise

Thermal effects remain one of the most challenging aspects of strain gage sensor performance. Historically, designers relied on external resistors to compensate for temperature-induced errors—adding further wiring complexity.

This case study highlights the use of strain gages with Effective Modulus Compensation (EMC), a technology emphasized by Yuval as a critical enabler.

Benefits of EMC Integration

• Intrinsic compensation for temperature-induced modulus changes

• Reduced reliance on trimming resistors

• Improved stability across fluctuating thermal environments

• Simplified bridge design

  
  

When EMC-enabled gages are paired with flex circuits, thermal performance improves without adding electrical complexity. This combination delivers consistent accuracy across wide temperature ranges—a key requirement in torque and force sensing applications.

6. Design Freedom: Rethinking the Wheatstone Bridge

Beyond process improvements, flex circuits introduce a more profound benefit: design freedom. Traditional wiring often constrains sensor geometry. Closely packed gage arms and short routing paths are chosen for practicality, not necessarily for optimal measurement.

As Yuval explains, flex circuits enable distributed Wheatstone bridge architectures, allowing:

• Increased spacing between gage arms

• Optimized placement for pure torque measurement

• Reduced sensitivity to bending and parasitic loads

Properly positioned and electrically connected strain gages can isolate desired signals while automatically rejecting unwanted inputs—such as bending or direct axial stress.

This capability is particularly valuable in torque sensors, where cross-sensitivity has historically been a major challenge.

7. Reliability and Signal Integrity

Removing hand soldering has a direct impact on long-term sensor reliability. Flex circuits provide:

• Uniform conductor resistance

• Stable connections under vibration

• Reduced risk of cold joints or solder fatigue

Commentary on the original post repeatedly emphasized how clean, repeatable assembly translates into better signal quality and fewer field failures.

For manufacturers, this means:

• Lower warranty exposure

• Fewer customer complaints

• Greater confidence in sensor-to-sensor repeatability

8. Connectivity and Future Integration

The discussion around Bluetooth connectivity and telemetry systems points toward the future. While the case study focuses on mechanical and electrical integration, the platform created by flex circuits makes advanced features easier to implement.

Depending on whether the sensor is rotating or stationary, options include:

• Hardwired connections

• Battery-powered telemetry

• Wireless data transmission

As Yuval notes, removing traditional wiring opens the door to space-saving, integrated electronics, enabling smarter sensors without compromising measurement integrity.

9. Industry Impact and Applications

The implications of this approach extend well beyond a single torque sensor design.

Potential applications include:

• Load cells for industrial weighing

• Embedded sensors in automation systems

• Aerospace force measurement

• Motorsports and drivetrain testing

• Structural health monitoring

By reducing assembly complexity while improving accuracy, flex circuit–integrated strain gage sensors provide a competitive advantage in both performance and manufacturability.

Conclusion

This case study demonstrates that innovation in sensor technology does not always come from new materials or exotic physics. Sometimes, it comes from rethinking the manufacturing process itself.

As articulated by Yuval , the combination of flex circuit integration, automated bonding, self adhesive assembly, and Effective Modulus Compensation represents a meaningful evolution in strain gage sensor design.

The result is a rare win-win-win:

• Lower manufacturing cost

• Higher reliability and repeatability

• Greater design freedom for future sensors

In an industry where precision is everything, simplifying the path to accuracy may be the most powerful innovation of all.

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