Mechanical Power Measurement at the Power Take-Off of an Agricultural Vehicle

Client

The client, a player in the agricultural sector specializing in the design and maintenance of agricultural machinery, sought to validate the mechanical performance of its tractors. Specifically, it needed to assess the power transmitted by the power take-off (PTO) – a critical element to ensure the efficiency of attached implements (mowers, shredders, etc.). Tests had to be conducted under real-world conditions, with requirements for traceability and repeatability of measurements to meet certification standards and farmers' expectations in terms of reliability.

Problem and Challenges

Simultaneous measurement of torque and rotational speed on a PTO presents several technical challenges:

• Harsh environment: vibrations, dust, and temperature variations typical of field testing.
• Required precision: evaluating mechanical power to the nearest watt (1 W), with a calibrated and linear measurement chain across the entire operating range (from 0 to 540 or 1,000 rpm, depending on PTO standards).
• Mechanical integration: adapting the measurement system to standardized transmission shaft interfaces without modifying the tractor or attached implement structure.
• Data acquisition and analysis: centralizing real-time measurements with clear display and logging capabilities for post-processing (curves, test reports).

PM Instrumentation Solution

PM Instrumentation proposed a turnkey solution, factory-calibrated and ready for use, combining:

• A bearingless torque sensor T27 (hollow flange model), designed to integrate directly onto the PTO shaft. Its bearingless technology eliminates parasitic friction and ensures high-precision dynamic measurement (class 0.1%).
• A dynamometer provided by the client, coupled at the output to simulate the load of the attached implement.
• An INF3-USB acquisition module, connected to a PC or tablet, enabling real-time visualization, curve plotting (torque/speed/power), and data export via dedicated software (included with the solution).
• Custom mechanical adapters, compatible with ISO standards for agricultural PTOs (series 1, 2, or 3), for plug-and-play installation.

The architecture features shielded cable data transmission (wireless option available upon request), with automatic compensation for thermal drift to maintain precision during extended test cycles.

Results and Client Benefits

The solution enabled the client to:

• Validate compliance of its tractors with manufacturer specifications, with a measurement uncertainty of less than 0.5% for mechanical power (kW).
• Automate test reports using integrated software, reducing data analysis time by 60% compared to manual methods (stopwatch + Excel calculations).
• Detect early anomalies in certain models (e.g., belt slippage at high speeds), avoiding post-sale warranty costs.
• Reuse the system for other applications, such as energy optimization of attached implements or the development of new transmissions.

The solution, delivered calibrated with a certificate, was deployed in less than 2 days without modifying the tested tractors. The client highlighted the robustness of the T27 sensor (IP67) and the simplicity of the software interface, suitable for both field technicians and R&D engineers.