Servo Motor / VFD Filters

PWM-driven motors - servo motors and variable frequency drives (VFD) - are a major source of electromagnetic interference (EMI) in equipment.  They also cause a number of problems in equipment, including damage to the motor’s bearings due to leakage current causing electrical discharge machining (EDM) and damage to motor’s insulation.  

"We tested the servo filter on another system, this time with Kollmorgen motors. We saw another significant reduction in noise on our signal"  (P.M.,U.K.)

OnFILTER’s patented SF-series filters servo and VFD motor filters substantially reduce high-frequency leakage currents in motors and in wiring, assisting in compliance with the requirements of IEC60034-17/-25 and NEMA MG 1-2016, as well as with NAMUR recommendations. They also reduce interfering high-frequency noise within the tool resulting from operation of PWM-driven motors.  

SF series filters greatly reduce high-frequency currents on equipment ground, as well as overall EMI in the tool, lowering risk of EOS and reducing errors in automated equipment and testers.

No Mechanical Fitting, No Wear, No Maintenance

OnFILTER' SF series filters have no mechanical coupling to the motors - all connections are electrical. 
Their cost of ownership is zero.​

We have all 3 filters installed on the machine. They seem to be working very well. It really suppresses the noise we were getting on the analog signals from the sensor (Director of Engineering, U.S.)

  • No mechanical attachments

  • No changes in software

  • No adjustments


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Basic Connection of Motor Filter
Basic Connection of Combo Motor/AC Filter
Servo/VFD Combo Filter Connectons
Reduction of EMI on AC power from servo/VFD drive with SF series filter
Servo / VFD Filter Connections
Servo/VFD Motor Ground Current Without Filter
Servo/VFD Motor Ground Current with SF Series Filter
Servo/VFD Drive Pulse Edge Modification

Ground Current Reduction with SF Series Motor Filters

Pulse Edge Modification

AC EMI Reduction

Application Notes
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Technical Articles

Interference Technology Magazine' Annual EMC Test and Design Guide, 2016

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