Avoiding erroneous test results

In order to avoid erroneous test results, particular attention must be paid to the following:

  • Before starting a static brake test, SEW‑EURODRIVE recommends moving the axes that are to be tested slightly, for example, by moving a short distance forward or moving to a specific position at which the brake test will be performed. The motion ensures that the axis being tested can move freely and that the devices involved in the test are available and functioning properly. The motion can be performed by the machine's automation system or as part of the brake test.
  • A software-based brake test usually cannot directly determine the braking torque that is present at the brake. In addition to the braking torque, a torque determined by the test also includes applicative torques, such as friction. Measuring tolerances of the measuring equipment that is used and a temperature-dependent torque characteristic of the motor can also lead to measurement deviations.
  • These applicative torques and the different meaning of the braking torques M2 and M4,100 °C can lead to the brake slipping, even significantly outside the tolerance range for the nominal braking torque Mbr.
  • Because of possible measurement deviations and the different meaning of the nominal braking torque Mbr and the static braking torque M4,100 °C, brake slippage can and may occur, even significantly outside the tolerance range for the nominal braking torque Mbr.
Temperature-dependent torque characteristic of the motor

For frequency inverters from SEW‑EURODRIVE, the control mode with encoder feedback assumes a drive that is warm from operation. With an increasing deviation of the motor's operating temperature from this assumption, a difference develops between the torque assumed by the control system and the torque actually generated by the motor. This is especially true for applications in low ambient temperatures and can have significant effects (e.g. in cold storage applications at less than 0 °C). This effect also occurs in drives with a lower thermal load than normal ambient temperature.

In such use cases, the motor must be equipped with a temperature sensor, e.g. Pt1000 or KTY, and evaluated via the frequency inverter. Through the temperature sensor, the frequency inverter takes into consideration the real temperature of the drive and compensates for the temperature-dependent torque characteristic using the control system.