Removing Noise From Power Line

[rhnrgn]

I made a motor driver card, which include dsPic30f015 and DRV8711 motor driver.

In factory where my customer going to use this card there are solenoid valves and when their solneoid valves activating there is a noise occurs. And this noise couses the mcu reset itself.


I attached my card's power stage and the osilloscope view of noise.

Do you suggest anything else to do or add to power stage.

I used chokes, ferrite beads but nothing has changed.






- - - Updated - - -

About oscilloscope view:

1_Each division refers to 1V. I took that voltage form 5V line after DC to DC converter. That means, voltage rises to 6.2 Volts at MCU power line.

 

[mrinalmani]

I have heard of similar complains before, a simple solution is to shield the MCU unit with a conductor.

 

[rhnrgn]

i think it is conducted noise, shielding is only a protection against Radiated noise

 

[Velkarn]

In your shematic i see no Y-capacitors. maybe this noise is from ground... what is your device housing (box)?

 

[rhnrgn]

I am also thinking about noise from ground, because when i searched internet i saw that solenoid relays couses Back EMF that means apply voltage to GND line.

Tomorrow i will try put a diode between 24V and GND line.

By the way, i have no cases and no earth ground. Because of my card will work at factory, i am not trust that factories earth ground system. There are alot of 3 fase motors and relays working at the same time.

Velkarn, can you explain a little bit about Y capacitors. I know that they are used between Power lines and earth ground.

 

[Velkarn]

Y-caps are built into your fn406 filter, but why you do not connect its "earth" contact?
and what you mean writing "i am not trust that factories earth ground system"?

 

[mrinalmani]

Oh, I thought you were speaking of radiated noise. If your problem is through conduction noise, first thing you should try is to add a filter capacitor on the input side.

 

[rhnrgn]

Oh, I thought you were speaking of radiated noise. If your problem is through conduction noise, first thing you should try is to add a filter capacitor on the input side.

I am not sure at all just investigating.

What do you mean filter capacitor on the imput side. Do you think that capacitors which i already put are not enough?

Y-caps are built into your fn406 filter, but why you do not connect its "earth" contact?
and what you mean writing "i am not trust that factories earth ground system"?

I mean, at that factory where i am working, they are not much concerned about earthing system.

I thought that, if i connect my card to that earth system, much more problem will may occur :roll:

- - - Updated - - -

 

[Velkarn]

on you shematic there is a earth ground symbol? where is this net connects?

 

[rhnrgn]

that is the ground of 5V stage

 

[schmitt trigger]

"I thought that, if i connect my card to that earth system, much more problem will may occur "

Then a dedicated ground for your system must be used. A ground spike driven into earth is required. If the factory has a solid concrete foundation, that may not be easy, but you could weld a cable to the steel columns.

Commercially available noise suppressors work very good, as long as they are properly earthed.
Another thing...I would not rule out radiated noise. If you have long wires coming out from your controller board, they will act as antennas.

 

[rado]

what about using a narrow band filter?

 

[rhnrgn]

you may right, earth ground is the last opportunuty to apply in order to get rid of that noise.

Here is another question, while i am searching internet i saw many power systems which has BJTs, power mosfets and diodes in it. Should i build a system which uses BJT and mosfet in order to remove that noise?

high voltage protection, high current protection etc.

Noise is very fast, above 10MHz. Can BJT and Mosfet power protection systems work?

Or am i understanding the prupose of that BJT and Mosfet systems wrong.



For example, The engineer before me designed that system. is it better? (He had problem too :razz



- - - Updated - - -

what about using a narrow band filter?

actually i prefered low pass filter, only need dc. there is a 1 ampere current to motor driver, 200ma current flow to MCU and Resistor is a problem there because of wattage issue.

What do you prefer? Can you explain a little?

 

[Velkarn]

in this shematic earth contact of EMC filter is connected, but image is cutted
one more thing, you writed that have no cases, and where is your device placed?

 

[mrinalmani]

Well I think I got it. Your motor itself is probably creating electromagnetic noise due to PWM which is tripping the MCU. This is a common problem with MCUs controlling inductive load.
SOLUTION:
Use a co-axial cable to drive the motor and connect the body (outer metal cover) of the motor to the neutral of the cable.

 

[rhnrgn]

in this shematic earth contact of EMC filter is connected, but image is cutted
one more thing, you writed that have no cases, and where is your device placed?

we are producing laser positioning systems to tire factories.

**broken link removed**

this photo of our system. my card is in it. System is hanging on a huge chasis and chasis has no connection to earth ground.

Between laser system and world only 3 cables. 1 power cable(shielded), 1 RS-232 cable, 1 Parallel port cable from PLC.

Shield of power cable is not connected anywhere =)

we are using rs232 cable only when we go to factory, otherwise rs-232 cable is npt connected.

Between pararllel port cable and MCU there are optocouplers. Pararlel port cables ground and MCU ground are isolated.

Between MCU and outside of the card there is only that power stage i sent.

Now, it is funny, while system working correctly, o solenoid relay activated which is away 10 meters away from our system, our MCU resets itself.

Solenoid relay and our system uses different AC to DC power supplys, only same thing is main 220V AC power line.

For me, this situation is very complicated and very thank you to read ti hole stuff.

They are loughing to my system, one of that workers told me that " we found a remote controler which resets your system" =) i like funny people hehe =)

- - - Updated - - -

Well I think I got it. Your motor itself is probably creating electromagnetic noise due to PWM which is tripping the MCU. This is a common problem with MCUs controlling inductive load.
SOLUTION:
Use a co-axial cable to drive the motor and connect the body (outer metal cover) of the motor to the neutral of the cable.

actualy not, because problem occurs while only solenoid valves activates.

 

[Velkarn]

Noise is very fast, above 10MHz. Can BJT and Mosfet power protection systems work?

imho it`s bad idea. because capacitor have to remove the noise. if capacitor do not work, mosfet or bjt shem would not help

- - - Updated - - -

System is hanging on a huge chasis and chasis has no connection to earth ground.

if this chasis made of metal, you should try to connect "earth" terminal of EMC filter to it

- - - Updated - - -

Between MCU and outside of the card there is only that power stage i sent.

ok, the connection is: AC line > AC/DC Supply (24V) > your power stage > your MCU ?

 

[rhnrgn]

ok, the connection is: AC line > AC/DC Supply (24V) > your power stage > your MCU ?

Yes, it is.

- - - Updated - - -

Another important point is, the source of noise is "i think" Back EMF. Because noise occur while de-energising solenoid valve. So solenoid valve may pumping voltage to notr line while de-energising.

- - - Updated - - -

Today, i will concentrate on grounding and post the results =)

2 questions,

1_what should be the size of Y caps? My EMC filter has 2.2 nF, is it enough?

2_Is there any special type of cable for grounding or can i use regular ones?

 

[mrinalmani]

I still suspect it is an electromagnetic noise arising from demagnetizing solenoids. The power cables are picking up the noise. Use a shielded power cable, such as a co-axial type.

 

[rhnrgn]

I still suspect it is an electromagnetic noise arising from demagnetizing solenoids. The power cables are picking up the noise. Use a shielded power cable, such as a co-axial type.

I will, and connect shield to earth ground from one end. i will share results