Methods to resolve EMI from induction motor

Hello everyone,

I am facing an issue with the operations of a circuit that is already been designed. The problem occuring is that my circuit works in an area comprising of inuction motor. If my circuit is running and suddenly the motor starts, its electromagnetic field affects the operation of the circuit for an instance and then works properly back again. Similar kind of situation occurs when the motor is switched off. I merged the circuit ground with the body ground but to no avail. Also, i tried to merge the grounds of the motor as well as of my circuit. But the situation still persists. I have shield and filters also available on my circuit but, I guess, they are also not helping me with the issue.

Kindly suggest me some other preventive measures to avoid this interference.

Thanks in advance.

are you using motor driver IC? Is the motor DC or stepper or etc..?

"affects the operation of the circuit" is it resetting the MCU?

Hello thanks for the reply. The motor is not operated from the circuit. But the circuit is near that motor which produces a strong electromagnetic field around it on startup and stopping process. And it does not resets my MCU, but the problem arises as this field somehow affects the analog signals on the circuit. Due to its effect, as I am using op-amp and comparators on the circuit, a little change in the signal triggers my output. And the situation is such that I even cannot increase the difference between the signals given to the comparator.

You may need more shielding of the circuit and better decoupling and filtering of the power and signals. Post the circuit diagram and connections to the outside world.

Do you have oscilloscope?
Can you measure the frequency of noise?
What is the frequency of your analog signal?

You can assume that contact arcing of the motor starter generates the interferences. They will travel down the line, couple to ground connections and nearby cables.

Interferences of this kind have to expected in an industrial (an to some extent in a domestic) enviroment at any time. Electronic equipment that is commercially produced and marketed has to pass tests that prove a certain degree of noise immunity. See e.g. IEC 61000-4-4 "Electrical fast transient/burst immunity tests".

If you are new to this problems, it's very likely that your circuit isn't designed aware of EMI.

man
this is very simple
isolate the supply also.
or
try to use optocoupler for motor switching

Hi,

First you need to know if the problem is influenced with direct electromagnetic field to your circuit, or if it is influenced with te connected wires.

For direct pcb: A proper small layout with proper ground plane and no "antennas" receiving the emi.

For influence by wire: use differential signaling, emi filters, ferrite beads, or glass fiber or pov for signal transmission...


Hope this helps
Klaus