For the test system, when it comes to test accuracy, people will ask how much the system accuracy can achieve. Because we all know that the accuracy of the test system is affected by many factors, by no means can the simple measuring meter accuracy be guaranteed. Today, let's talk about how to ensure the torque measurement accuracy in the motor test system.
In the motor test system, the measurement of torque is often achieved through torque sensors. The following is a typical motor torque test method:
The motor under test is connected to the torque sensor through the coupling, and the other end of the torque sensor is connected to the load motor through the coupling. When the system is working, the motor under test works in the speed loop (or the torque loop), the load motor works in the torque loop (or the speed loop). The torque sensor measures the motor torque and transmits the torque value to the measuring instrument through electric signal.
After understanding the torque testing process, we can find the key factors of torque testing.
- The measurement accuracy of the torque sensor.
- The measurement accuracy of the test instrument.
- The torque loading accuracy of the motor (the load under test).
- The mechanical installation accuracy of the system.
Next, we analyze every factor point in turn.
1. The measurement accuracy of the torque sensor.
Some people say that the torque sensor is very simple. Each sensor has a nominal accuracy. You can know it directly by looking at its manual datasheet. It is true that all the torque sensors have their nominal measurement accuracy. But torque sensors have their measurement ranges. And how to choose the appropriate measuring range is also a crucial factor. Here we recommend a "three-five principle". 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 recommended that the measurement range is not less than one-third of the range. For example, the measuring range of a torque sensor is 1Nm, it is recommended to measure a minimum value of 0.33Nm. When the measuring torque is above 1Nm, in order to ensure the measurement accuracy, it is recommended that the measurement range is not less than one-fifth of the measuring range. For example, if the torque sensor has a range of 10Nm, it is recommended to measure a minimum value of 2Nm. Only in this way can the measurement accuracy of the torque sensor be guaranteed.
2. The measurement accuracy of the test meter.
The traditional motor test system uses different instruments such as electrical parameter meters and torque meters to measure the power, torque and speed parameters separately. The measurement accuracy can be guaranteed in the steady state. Once the measurement of transient parameters is carried out, the measurement accuracy will be greatly affected. Therefore, in the case of transient testing, high-precision measuring instruments such as digital torque meter must be used to simultaneously measure power, torque and speed to keep the measurement data accurate.
3. The torque loading accuracy.
When we can guarantee the measurement accuracy, the loading accuracy of the system must be considered. For example, in the test of the system, when we want to test the 5N.m torque point, the controller sends instructions to control the motor to load. At this time, the system must be able to monitor the actual torque synchronously, and adjust it in real time through PID to ensure the output torque at 5Nm (the size of the error depends on the degree of PID control optimization). The fourth point is the mechanical installation accuracy of the system. The low mechanical installation accuracy means that the deviation of the mechanical centering angle of the test bench is large. During the long-term operation of the motor test system, the test bench will be deformed, abnormal vibration, screw off, coupling broken, etc. Therefore, the alignment accuracy of the test system including torque sensor and motor must be guaranteed, otherwise everything done before will be in vain.