In the motor test system, the measurement of torque is often achieved by dynamic torque sensors.
The motor under test is connected to the dynamic torque sensor through the coupling, and the other end of the sensor is connected to the load motor through the coupling. When the system is operating, the motor under test works in the speed ring (or torque ring), the load motor works in the torque ring (or speed ring), and the sensor measures the torque and transmits the torque value to the measuring instrument through the signal.
After understanding the torque test process, we can find the key influencing factors of torque test accuracy: 1. The measurement accuracy of the dynamic torque sensor; 2. The measurement accuracy of the test instrument; 3. Torque loading accuracy of the motor (measured and loaded); 4. The mechanical installation accuracy of the system. Next, let's analyze each element point.
The first is the measurement accuracy of the dynamic torque sensor
Some people say that torque sensors are very simple, and each sensor has a nominal accuracy, which can be known by directly checking its manual. It is true that both domestic and foreign dynamic torque sensors have their nominal measurement accuracy, but torque sensors have their measurement range, and how to choose the right range is also a crucial element.
The so-called "three-five principle" is that when the test torque is within 1N.m, in order to ensure the measurement accuracy, it is advocated that the measurement scale is not less than one-third of the range, for example, the sensor with a range of 1N.m advocates the minimum measurement to 0.33N.m; When the measurement torque is more than 1N.m, in order to ensure the measurement accuracy, it is recommended that the measurement scale is not less than one-fifth of the range, for example, for the sensor with a range of 10N.m, the minimum measurement is 2N.m. This is the only way to ensure the measurement accuracy of the dynamic torque sensor.
The second is the measurement accuracy of the test instrument
The traditional motor test system is to use discrete instruments such as electrical parameter table and torque meter to measure the electrical parameters and torque speed parameters respectively, and the measurement accuracy can be ensured in the steady state, and the measurement accuracy will be greatly affected once the transient parameters are measured. Therefore, in the case of transient test, it is necessary to use high-precision measurement instruments such as power profiler to simultaneously measure the electrical parameters and torque speed test to maintain the accuracy of the measurement data.
Then there is the torque loading accuracy
When we can ensure the measurement accuracy, it is necessary to consider the loading accuracy of the system. For example, in the process of testing, when we want to test the 5N.m torque point, the controller sends instructions and controls the motor for loading, at this moment the system must be able to monitor the actual torque synchronously, and adjust it through the PID in real time to ensure that the output torque is 5N.m (the size of the error depends on the optimization degree of PID control).
Fourth, the mechanical installation accuracy of the system
The low accuracy of mechanical installation means that the mechanical alignment angle deviation of the test bench is large, and the motor test system will present problems such as test bench deformation, abnormal vibration, screw dropping, and coupling fracture during long-term operation. Therefore, it is necessary to ensure accurate alignment, otherwise everything that has been done up to the moment will be in vain.
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