Cause : Encoder fault comes when  he drive is unable to receive a valid signal from the speed encoder, hindering its ability to control the motor speed accurately.

F051 fault in siemens master drive indicate a speed encoder fault. The speed encoder, also known as a tachometer, is a crucial sensor that provides feedback on the motor shaft's rotational speed. This information is essential for the drive to maintain precise motor control.

1. Check the following parameters:
   - P130 Src SpdActV
   - P151 Pulse #
   - P138 AnalogTachScale
   - P109 Motor #PolePairs
   The product of P109 and P138 must be smaller than 19200.
2. Check or replace tachometer.
3. Check connection to tachometer.