How to detect noise on a line and filtering - Page 1
Forum section: electronics / beginners

author: Yaro
author_rank: Contributor
timestamp: January 21, 2015, 10:23:14 am
content: 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.

author: HalfSpace
author_rank: Regular Contributor
timestamp: January 23, 2015, 08:17:03 pm
content: 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

author: Yaro
author_rank: Contributor
timestamp: January 24, 2015, 09:15:58 am
content: 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?

author: HalfSpace
author_rank: Regular Contributor
timestamp: January 24, 2015, 09:15:41 pm
content: 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

author: beauty2003tt
author_rank: Contributor
timestamp: March 26, 2015, 03:40:23 am
content: Could anyone reply me more information of Hantek6022BE? Is it good for a beginner? I'm considering to buy one.Thanks

author: codeboy2k
author_rank: Super Contributor
timestamp: March 26, 2015, 10:27:56 pm
content: Quote from: beauty2003tt on March 26, 2015, 03:40:23 amRead 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-20mhz-usb-dso/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/testgear/hantek6022bl-2ch16logic-compatible-with-saleae/

author: beauty2003tt
author_rank: Contributor
timestamp: March 27, 2015, 06:41:19 am
content: Quote from: codeboy2k on March 26, 2015, 10:27:56 pmThank you very much!