AGND+DGND+EARTH=NOISE....true or false?

Hi All,
In our Hurco Milling Servo drives are such that
digital and analog grounds are internally shorted i.e
DAC output of STG,tacho of motor ,limit switches and
encoder have common grounds which are then tied up to
Machine's body which is connected to earth, We are
facing problems of Noise I was wondering if this is
the reason ??

Thanks
Babar

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