I have a 55kW Danfoss variable speed drive to control a 440V / 3Ph / 3000 rpm motor. Wiring is exactly as in the manual including the last earth point.

I also have a Flowmeter (FM) near the drive at about 1M distance. The FM works by picking up pulses from a rotating gear ( 5 to 50 Hz range ) and the mounted electronics converts this to a 4-20mA signal.

Whenever I switch on the drive, the FM readings become unsteady. In fact as soon as the drive is switched on, the 0.00 lpm display of FM become 1.50 lpm. It is obvious that the pick up coil is picking up noise.

Any ideas to kill this noise ??

The FM is fed by 24Vdc from a MeanWell SMPS through a 2 core shielded wire. In such instances is it better to connect the shield to the DC ground ( 0 Volt terminal)of SMPS or to the panel earth ??

Thanks

Raghu