Author Topic: How to detect noise on a line and filtering  (Read 1933 times)

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Offline Yaro

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How to detect noise on a line and filtering
« on: January 21, 2015, 09:23:14 pm »
Hi All,

I want to ask how I can detect noise on a line and how to determinate when it may have effects on digital or analog connection quality. For example, I've a digital and an analog line and a 100Khz noise on this 2 lines. How I see this noise on oscilloscope? Also, I was interested in Hantek 6022be but i've read there is a noise of about 20mV on input signal, should this affect my noise detection?

I have also a question on filters, assume I want to use a low pass filter that suppress high freq. , but if I use this filter before an MCU  power supply that work at in Mhz range, there may be problems? Inductor may act like a resistance or something like this?

Thank you.
 

Offline HalfSpace

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Re: How to detect noise on a line and filtering
« Reply #1 on: January 24, 2015, 07:17:03 am »
Hi Yaro,

What do you mean by noise on a line? Are you talking about noise on a mains power line e.g. 110V / 240V  AC, a telephone line or something else?

HalfSpace :)
"He who asks a question is a fool for five minutes; he who does not ask a question remains a fool forever."
 

Offline Yaro

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Re: How to detect noise on a line and filtering
« Reply #2 on: January 24, 2015, 08:15:58 pm »
For noise I mean EMI noise and inside circuit noise like generated by a stepper motor. I want avoid to use external shield and want to use an inductor filter, but how this may affect digital parts of the circuit?
 

Offline HalfSpace

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Re: How to detect noise on a line and filtering
« Reply #3 on: January 25, 2015, 08:15:41 am »
Hi Yaro,

Using an oscilloscope to detecting EMI noise can be difficult; a spectrum analyzer is a better choice as it will display the frequency of the EMI so you design a low pass filter with the correct roll off frequency to suppress it. Here is a link to build some simple magnetic field probes that can be used with spectrum analyzer to detect EMI. http://www.compliance-club.com/archive/keitharmstrong/emc_testing1.html. The probes can be used with an oscilloscope if you wish but should be terminated into 50ohms.

Using an LC type low pass filter on a DC power supply rail is ok but use a PI type. For a driving circuit use a T filter. If the EMI is a radiated magnetic field LC filters may not work and a metal shield might be the best choice.

As to how these filters may affect the digital part of your circuit, we will need to see the design to make a judgment.

HalfSpace  :)
"He who asks a question is a fool for five minutes; he who does not ask a question remains a fool forever."
 

Offline beauty2003tt

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Re: How to detect noise on a line and filtering
« Reply #4 on: March 26, 2015, 02:40:23 pm »
Could anyone reply me more information of Hantek6022BE? Is it good for a beginner? I'm considering to buy one.
Thanks :)
 




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