In many applications, such as measuring the tightening force of high-power turbines or medicine containers, torque is the most important measurement. In principle, torque is the product of force and lever arm, but for high-precision torque measurement, especially in rotating applications, a high-precision torque sensor is required.
This paper focuses on torque testing of large turbine engines, particularly jet engines. The project aims to create a test bench to optimize turbine engines using the obtained torque data, thereby improving fuel efficiency. Therefore, obtaining accurate torque measurements is a crucial component of this project.
The test requires torque sensors with ranges of 200 N·m, 1 kN·m, 2 kN·m, and 130 kN·m. The three smaller range torque sensors have identical geometry and operate at speeds up to 22,000 RPM. The largest torque sensor operates at 4,000 RPM. Like the rest of the test bench, the torque sensors need to be extremely reliable and durable, as they are often intended to operate for several months. To prevent failure of any output, each sensor has two independent torque outputs with backup.
Previously, the test bench used non-rotational torque measurement technology—a force sensor and a lever arm, calculating the torque by multiplying the force by the lever arm. This testing technology, which has existed for half a century, has its own advantages. For example, calibration is simple, and overload protection is relatively easy. However, it has one major drawback: because the force sensor is not on the rotating shaft, accurate alignment cannot be achieved.
There is a large measurement error.
Another drawback of this method is its low dynamic response (only 20Hz). This is because the mass of the force gauge acts as a low-pass filter, increasing the uncertainty in torque measurement. Additionally, the force gauge must be mounted on a bearing, and rotation causes friction on the bearing, requiring regular maintenance.
The current measurement technology only requires the installation of a torque sensor , which consists of a rotor and a stator. It is powered and transmits digital signals through wireless telemetry technology, and because it uses non-contact measurement technology, it is maintenance-free.
Using an online torque sensor offers several advantages. For example, it provides high dynamics—its response frequency reaches up to 6kHz, allowing for the measurement of true dynamic torque. In contrast, traditional lever technology has a response frequency of only 20Hz.
Furthermore, there's no need to consider bearing friction and maintenance issues. In-line sensors offer higher dynamic response accuracy. However, in-line torque sensors also have their drawbacks: alignment is more difficult, and overload prevention is crucial. Especially when system calibration is required, the rotating shaft may need to be modified or the torque sensor removed.
For similar applications, more consideration is needed during the design and development phases. If the sensor rotor is made of titanium instead of stainless steel, the rotary torque sensor will have an advantage due to its lower moment of inertia. Lighter titanium and a shorter length will result in a lighter overall drive system. It also makes it easier to avoid the "critical speed" problem of the rotating shaft during testing. The critical speed (rotational speed) is a point where the rotating shaft becomes unstable, producing harmonic vibrations. A shorter, stiffer, and lighter weight is to avoid unnecessary vibrations and jumps, which increase measurement uncertainty and the likelihood of system failure. In-line torque sensors generally use AC excitation to improve the sensor's anti-interference capability. This will improve the accuracy of torque measurement, especially at very low speeds.
To meet diverse customer testing requirements, BIU Sensors can customize torque sensors, including those with higher accuracy, dual outputs, extended lengths, and boltless designs.
Bearingless design reduces customer maintenance costs. Two strain gauge circuits provide higher measurement accuracy. A titanium rotor reduces sensor weight and increases rotational speed. Customized length and boltless mounting exclude critical speeds from the measurement range. These features reduce measurement uncertainty and improve accuracy, allowing customers to obtain more reliable data to improve product efficiency. Recently, we have standardized our custom sensor solutions to meet diverse customer requirements for higher accuracy and higher rotational speeds.
