Rotor unit
Mounted directly on the shaft, it powers the strain gauges, captures sensor signals and digitizes them at the rotating measurement point.
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Technology guide
Contactless torque measurement — principles, methods and industrial applications
Torque is the truth signal in the drivetrain. Contactless telemetry measures it directly on the rotating shaft — without slip rings, batteries, or mechanical signal pickup.
Strain gauge measurement directly on the rotating shaft
Inductive power transfer instead of batteries or slip rings
Digital signal acquisition on the shaft
Applications in automotive, test benches and industry
Principle
What is contactless torque measurement?
Contactless torque measurement captures torque on a rotating shaft without mechanical contact between the rotating measurement part and the stationary evaluation unit.
The proven sensor principle is still the strain gauge. Under torsion, the shaft deforms minimally, the strain gauge changes electrical resistance, and torque is calculated from that signal. The progress is in power transfer, digitization and data transmission.
In telemetric torque measurement, a stator antenna supplies the rotor electronics inductively. At the same time, the rotor unit sends digitized measurement data back to the control unit. No brushes, no slip contacts, no battery.
Stator unit
Creates the inductive field for power transfer and receives the digitally transmitted measurement data without contact.
Control unit
Controls power transfer, processes data and provides values as analog or CAN bus signals for test bench and vehicle use.
Slip ring vs. telemetry
Measurement methods compared
Industrial measurement tasks are not decided by lab values alone, but by performance at speed, with oil, temperature, relative motion and maintenance pressure.
Telemetry with strain gauges
- Principle
- Strain gauges on the shaft plus inductive power and data transfer
- Strength
- Precise, maintenance-free and robust at high speeds
- Limit
- Application and layout must match the specific shaft
- Fit
- Automotive, test benches, endurance testing, machinery
Slip ring
- Principle
- Strain gauge signal through mechanical contacts
- Strength
- Known method for clean lab conditions
- Limit
- Wear, signal noise and maintenance in real environments
- Fit
- Moderate speeds, short tests, simple lab setups
Magnetoelastic
- Principle
- Change of magnetic properties under mechanical stress
- Strength
- Contactless and no applied strain gauges
- Limit
- Only for suitable shaft materials and usually less flexible
- Fit
- Production-adjacent applications and condition monitoring
Optical
- Principle
- Torsion via light signals or phase shift
- Strength
- Theoretically precise in very clean environments
- Limit
- Sensitive to contamination, oil mist and vibration
- Fit
- Research and clean special setups
Benefits of contactless telemetry
Maintenance-free
No brushes, slip contacts or mechanical abrasion — important for endurance runs and long-term tests.
High rotational speed
Inductive telemetry avoids the mechanical limits of classical slip rings in dynamic drivetrains.
Robust in real environments
Oil, humidity, temperature, contamination and vibration are considered in application and protection.
No batteries
The rotor unit is inductively powered. Battery replacement and battery-related measurement failures are avoided.
Anti-EMC for e-drives
Measurements near inverters and high-voltage environments need interference-resistant data transfer.
On-shaft digitization
Tiny analog signals are digitized directly on the shaft before contactless transmission.
Air-gap tolerance
Larger transfer distances help when rotor and stator move relative to each other.
Operating data visibility
Temperature, supply status and signal quality help assess the measurement chain during tests.
Applications
Typical applications
Contactless torque measurement is strongest where the measurement point rotates, is hard to access, or must remain stable over long test durations.
Vehicle testing
Automotive & e-mobility
Torque measurement on side shafts, cardan shafts, transmission inputs and outputs, and e-drives — including transient states, recuperation and EMC-loaded environments.
Test bench
Test benches
Engine, transmission, component, brake and dynamometer test benches need reproducible torque data across many measurement cycles.
Machinery
Machinery & industrial drives
Torque traces support load spectra, condition monitoring and early detection of wear or misalignment.
Wind power
Wind, aerospace and high-end validation
High loads, relative movement and strict documentation requirements call for robust measurement chains with traceable operating parameters.
From measurement task to ready-to-use solution
AXON treats torque measurement as a complete measurement chain: sensor, telemetry, mechanical integration and calibration.
1. Define the task
Clarify shaft, speed range, torque range, temperature, media exposure, installation space and interfaces.
2. Design strain gauges and telemetry
Select strain gauges, rotor unit, antennas, control unit and protection for the application.
3. Integrate mechanically
Position rotor and stator sides so power transfer, data transmission and installation space work together.
4. Calibrate and commission
Check, calibrate, document and hand over the measurement chain for test bench, vehicle or machine.
System selection
Which AXON system fits the task?
The right system depends on whether the task needs torque only, multiple strain gauge channels, additional temperature or a measurement flange.
AXON J1DB
Universal 1-channel strain gauge telemetry transmitter for torque measurement.
Details
AXON J2D / J2DT
Two-channel strain gauge telemetry, optionally combined with temperature.
Details
AXON JXTH
Multi-channel telemetry for temperature measurement on rotating components.
Details
AXON AT10
Plug-and-play measurement flange for existing torque flange environments.
DetailsFAQ: contactless torque measurement
Why is contactless torque measurement more robust than a slip ring?
Because power and data are transmitted without mechanical contacts. There are no brushes, no contact wear and fewer signal issues from transition resistance.
Is torque measured directly?
The shaft torsion is measured via strain gauges. Torque is then determined through calibration and the measurement chain.
What data does AXON need for a layout?
Useful inputs include shaft or component data, expected torque range, speed, installation space, temperature, media exposure and the required interface to the test bench or vehicle.
Plan torque measurement for your rotating application
Describe shaft, installation space, speed, temperature and interface. AXON will assess which telemetry and strain gauge application makes sense.