Rotary encoder, monitoring function is actuated by mistake

Which products are concerned?
8400 StateLine
8400 HighLine

What happens?
Due to the monitoring logic of the speed encoder, it may happen that the encoder evaluation responds although the encoder has not failed and is not defective. In these cases, the frequency inverter will erroneously generate an error message although no error has occurred. This response is activated by a short-time exceedance of the difference between set and actual speed.

When does the problem occur?
The problem occurs when:

• short drive acceleration times are required (e. g. for very dynamic start or braking processes)
• short-time, sudden load conditions occur on the motor shaft (sudden rise of the load torque)
• dynamic positioning processes (only 8400 HighLine) are selected in which the P position controller provides for a very fast rise of the speed setpoint and the actual speed cannot follow this setpoint correction

Diagnostics options?
Monitoring the actual speed (C00051) during operation.

Short-term measures/recommendations?
Set the speed encoder monitoring to  'WARNING' (C00586 = 5) or deactivate it completely (C00586 = 0). Set the frequency limitation (C00910) of the frequency inverter to the maximum system frequency to avoid possible damage to the system.

Conclusion:
When the monitoring function is deactivated (or 'WARNING' is set), the frequency inverter cannot be destroyed because other monitoring functions protect it from overload. The speed encoder can, however, no longer be monitored by the frequency inverter. If the plant design requires this monitoring function, it must be provided externally. Possible components are, e. g. available from Motrona GmbH.