Rocky Mountain Chapter EMC Society |
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Our last meeting was.. The Mysteries of Grounding Download the
presentation here Presenter: Daryl Gerke, PE a principal in Kimmel Gerke Associates, Ltd Date : September 17th 2002 Location : Courtyard by Marriott,
Courtyard 948 West Dillon Road Louisville, CO What we saw: We had one of our most entertaining and informative meetings when Daryl Gerke went where most engineers fear to tread and unveiled the mysteries of grounding. In the very beginning of the talk Daryl pointed out what we knew all along but only whispered in dark corners; that is that grounding is like a sewer system and al lot of EMC Engineering is really sewer work! The sewer analogy actually worked very well as Daryl probed the eternal question of what actually is a ground and pointed out that used current, like used water, still want to flow. Naturally if there are any impedances in the ground (or holes) then the current will leak out and unwanted radiation will result. Daryl then went into the design requirements of different ground types such as safety, lightning, R.F, ESD and EMI with examples of each. (BTW - Crouch do NOT lie down if you are caught outside in a lightning storm - thanks Daryl). Daryl, then went into some detail in unraveling the concepts of single point grounding and multipoint grounding. But when to use which one? We then learned another secret to EMC Engineering - (i) look studious, (ii)stroke your chin and then (iii) say - "It depends". When reviewing a ground design, first review it at 60Hz and then review its performance at 100MHz and compare it to the desired grounding goal. As a rule of thumb use 10kHz as the dividing line between low frequency single point grounded signals and high frequency multipoint grounds. Daryl the presented a variety of system grounding problems with solutions ranging from balanced circuits at low frequencies, with optoisolators, transformer coupling, and grounding the return at only one end. At high frequencies Daryl recommends the use of multipoint grounding such as planes or grids with ground points spaced no further than 1/20 of a wavelength apart and bond straps with a length-to-width ratio no greater than 5:1. But Daryl saved the best for last. To really excel as an EMC Engineer, when presented with a problem, look studious, stroke your chin and say: " It must be a Grounding problem!" |
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