enter image description here A single-ended earth grounded PCI data acquisition board's analog inputs and outputs are controlled by a PC. The daq board has also analog outputs. One of the analog output is controlling the motor speed. It does that by controlling the 0-10V VFD drive input via an isolation amplifier which isolates the grounds of VFD and the daq system. I tried to draw the system above. The mootor and VFD are close to eachother and the DAQ system is 20m far away.

The fan motor is a 3-phase (3-50Hz) 22kW AC motor prim delta: 380V. This is the VHD drive in use.

I'm trying to prevent noise or common mode noise.

Recently I've been told to check the potential difference between the daq earth and the VFD earth grounds.

How should the system be properly grounded to earth?

Should the potential difference between the earths be zero?

Does anyone have experience with such system?

  • \$\begingroup\$ Assuming from your drawing that the ISO amp is near the DAC. \$\endgroup\$ – Chris Knudsen Dec 13 '17 at 13:38
  • \$\begingroup\$ Check the specs of the iso amp. Is it true 3-way isolation (power, input and output)? Many aren't. Perhaps consider a 4..20mA transmitter iso module from the DAC, with a 4..20mA to 0-10V receiver isolator near the VFD (all with 3-way isolation). 4..20 loops do well in noisy industrial environs. Yes, motor and VFD should be Earthed. Yes, PC & DAQ should be Earthed (IMO). There are ways to lift the PC from Earth with an ISO transformer. Try not to go there... \$\endgroup\$ – Chris Knudsen Dec 13 '17 at 13:44
  • \$\begingroup\$ Yes all grounds isolated here is the data sheet prelectronics.com/filearkiv/PDF/2200%20series/2284/Manual/… \$\endgroup\$ – Genzo Dec 15 '17 at 3:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.