EEVblog Electronics Community Forum

Electronics => Beginners => Topic started by: Yaro on January 21, 2015, 10:23:14 am

Title: How to detect noise on a line and filtering
Post by: Yaro on January 21, 2015, 10:23:14 am
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.
Title: Re: How to detect noise on a line and filtering
Post by: HalfSpace on January 23, 2015, 08:17:03 pm
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 :)
Title: Re: How to detect noise on a line and filtering
Post by: Yaro on January 24, 2015, 09:15:58 am
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?
Title: Re: How to detect noise on a line and filtering
Post by: HalfSpace on January 24, 2015, 09:15:41 pm
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. (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  :)
Title: Re: How to detect noise on a line and filtering
Post by: beauty2003tt on March 26, 2015, 03:40:23 am
Could anyone reply me more information of Hantek6022BE? Is it good for a beginner? I'm considering to buy one.
Thanks :)
Title: Re: How to detect noise on a line and filtering
Post by: codeboy2k on March 26, 2015, 10:27:56 pm
Could anyone reply me more information of Hantek6022BE? Is it good for a beginner? I'm considering to buy one.
Thanks :)

Read these links here on the forum.  Others have already discussed it well.

https://www.eevblog.com/forum/testgear/hantek-6022be-will-it-work-for-me/ (https://www.eevblog.com/forum/testgear/hantek-6022be-will-it-work-for-me/)
https://www.eevblog.com/forum/testgear/hantek-6022be-20mhz-usb-dso/ (https://www.eevblog.com/forum/testgear/hantek-6022be-20mhz-usb-dso/)
https://www.eevblog.com/forum/testgear/hantek-6022be-20mhz-usb-scope-review-ish/ (https://www.eevblog.com/forum/testgear/hantek-6022be-20mhz-usb-scope-review-ish/)
https://www.eevblog.com/forum/beginners/hantek-oscilloscopes/ (https://www.eevblog.com/forum/beginners/hantek-oscilloscopes/)
https://www.eevblog.com/forum/testgear/hantek6022bl-2ch16logic-compatible-with-saleae/ (https://www.eevblog.com/forum/testgear/hantek6022bl-2ch16logic-compatible-with-saleae/)
Title: Re: How to detect noise on a line and filtering
Post by: beauty2003tt on March 27, 2015, 06:41:19 am
Could anyone reply me more information of Hantek6022BE? Is it good for a beginner? I'm considering to buy one.
Thanks :)

Read these links here on the forum.  Others have already discussed it well.

https://www.eevblog.com/forum/testgear/hantek-6022be-will-it-work-for-me/ (https://www.eevblog.com/forum/testgear/hantek-6022be-will-it-work-for-me/)
https://www.eevblog.com/forum/testgear/hantek-6022be-20mhz-usb-dso/ (https://www.eevblog.com/forum/testgear/hantek-6022be-20mhz-usb-dso/)
https://www.eevblog.com/forum/testgear/hantek-6022be-20mhz-usb-scope-review-ish/ (https://www.eevblog.com/forum/testgear/hantek-6022be-20mhz-usb-scope-review-ish/)
https://www.eevblog.com/forum/beginners/hantek-oscilloscopes/ (https://www.eevblog.com/forum/beginners/hantek-oscilloscopes/)
https://www.eevblog.com/forum/testgear/hantek6022bl-2ch16logic-compatible-with-saleae/ (https://www.eevblog.com/forum/testgear/hantek6022bl-2ch16logic-compatible-with-saleae/)


Thank you very much!