Torque, moment, torque difference and measurement

　　The three words moment, torque and torque are often used interchangeably by engineers in the industry. Everyone thinks that these three are the same concept, and only pays attention to their rated value and peak value during testing. Today, let's briefly analyze the differences between the three and the related test items.

　　1. The source and difference of moment, torque and torque

　　When we talk about torque, we immediately think of levers. The product of the force and the distance perpendicular to the direction of the force is called torque. The unit of torque is Newton-meter.

　　Figure 1 Lever torque

　　Torque is the moment of rotation. For a rotating object, if the center of the axis is regarded as the fulcrum, the product of the force on the circumference of the rotating object and the distance perpendicular to the center of the axis and the direction of the force is called torque. When a cylindrical object is subjected to force but does not rotate, the object only undergoes elastic deformation due to torsion after being subjected to force. The torque at this time is called torque.

　　Figure 2 Torque and moment

　　Therefore, strictly speaking, the running motor can only be called "torque". "Moment" or "torque" are not very appropriate. However, these three names have been used for a long time, at least sixty or seventy years, so no one deliberately corrects them.

　　2. Methods and trends of motor torque measurement

　　At present, the torque of motors in the industry is generally measured directly by torque meters. There are also many cutting-edge measurement items for motor torque, such as torque-angle characteristics, torque fluctuation, cogging torque, friction torque test, etc.

　　For stepper motors or switched reluctance motors, the angle θ between the stator magnetomotive force FS and the rotor magnetomotive force Fr is of particular concern, rather than the power angle σ that is well known in ordinary synchronous motors. In stepper synchronous motors, the angle θ is a very important parameter, called the torque angle, and the relationship between the motor torque and the torque angle is called the torque angle characteristic. The figure below is the torque angle characteristic curve obtained by the MPT1000 motor test system of Zhiyuan Electronics.

　　Figure 3 Zhiyuan Electronics moment-angle characteristic test

　　The output torque of the motor changes with the armature angular position, showing a small fluctuation value △M. The torque fluctuation coefficient is usually used to measure this quality of the torque motor. Zhiyuan Electronics uses a load motor to apply the maximum torque specified in the continuous working area to the motor under test, controls the motor to run at the lowest speed, and uses a torque sensor to record the torque of the motor when it runs for one cycle. By recording the maximum torque and minimum torque, the torque fluctuation coefficient can be calculated.

　　Figure 4 ZLG Zhiyuan Electronics Torque Ripple Test

　　3. MPT Hybrid Motor Test System

　　With its in-depth understanding and long-term accumulation in the fields of power analysis and motor measurement, ZLG Zhiyuan Electronics has integrated the concepts of instrument design and system integration to launch the epoch-making MPT hybrid motor test system, which has achieved a comprehensive innovation in the motor test system in terms of control accuracy, analysis capabilities and international standard support. It is used to meet the in-depth requirements of motor testing in different industries and realize more professional and user-friendly functional customization services. At present, the MPT hybrid motor test system supports the following test items, and can also provide users with customized test functions.

　　Figure 5 MPT1000 test items