I love the "ohms per square" term. It drives the non-EE nuts. John Shinn, P.E.
From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Conway, Patrick R (Houston) Sent: Friday, June 23, 2006 9:22 AM To: Sudhakar Wasnik; John Woodgate; emc-p...@ieee.org Subject: RE: [JunkMail] 1500 ohms 100 pF gun? If the clear, logical explanation does not work, then try my fall-back plan: If it is an ME try this: "Oh, think of ESD as the electrical equivalent to the study of thermal gradients in non-homogeneous stratified media". (or pick another incomprehensible subject in their area of expertise- but you gotta do it with a straight face!!) My favorite story about the EE / ME rift is about units. I know more than a few ME's who just cringe when they hear the term from shielding: "Ohms per square". They are left hanging, waiting for you to complete the sentence. "Ohms per square... WHAT?" they ask. They just can't conceive a system of measurement that has a variable in the units! Can't help but find humor in that. Best Regards, Patrick Conway, NCE. 281.514.2259 281.524.5473 (fax) p.con...@hp.com From: Sudhakar Wasnik [mailto:swas...@sandisk.com] Sent: Friday, June 23, 2006 3:58 AM To: Conway, Patrick R (Houston); John Woodgate; emc-p...@ieee.org Subject: RE: [JunkMail] 1500 ohms 100 pF gun? Thank you Sir, I have toughest time of my career explaining this to my co-workers (Mechanical engineers: I apologize for If unknowing I will hurt the feeling of any mechanical engineer) who possess mysterious thinking about ESD. Sudhakar Wasnik From: Conway, Patrick R (Houston) [mailto:p.con...@hp.com] Sent: Thursday, June 22, 2006 12:47 PM To: Sudhakar Wasnik; John Woodgate; emc-p...@ieee.org Subject: RE: [JunkMail] 1500 ohms 100 pF gun? Ah, ha. Glad to find another engineer who thinks like I do - unconventional! anecdote- One time I visited a large, well respected IT company who was having an ESD problem with a new product. They could not release to production because they could not pass the ESD test. I made one change to their test procedure and they were able to pass. Nothing spectacular really, just a little applied unconventional thinking! I observed that their test engineer was doing the test and then discharging the EUT after each strike (battery operated EUT). The EUT passed each and every strike, but had an upset during his connection of the discharge wire. The discharge wire had no resistors in line. It was a straight dump to the horizontal coupling plane. I explained to the team, showed them the failures were only during post-test charge dump. I explained that the discharge event is uncontrolled. It could have more ore less rise time, more or less fall time, more or less peak amplitude. It is uncontrolled. If they wanted to test with that waveform- no problem. But it is not required for CE Mark (their target). Everyone was happy! Much rejoicing. Anyway- clear evidence that even the post-test discharge needs to be done correctly. And, evidence that more training is always a good thing! Best Regards, Patrick Conway, NCE. 281.514.2259 281.524.5473 (fax) p.con...@hp.com From: Sudhakar Wasnik [mailto:swas...@sandisk.com] Sent: Friday, June 23, 2006 3:14 AM To: Conway, Patrick R (Houston); John Woodgate; emc-p...@ieee.org Subject: RE: [JunkMail] 1500 ohms 100 pF gun? You are correct sir, The current flow is from higher potential to lower potential. So with repetitive zaps, the system accumulates the charge (potential) higher than Gun potential, So current will flow from Object being zapped to the Gun (Source). That's why standard requires removing the unspent charge from the EUT by manual discharge before applying next zap. If we consider this is same as lightening event, Then John is correct. It is mysterious even to think that the earth (Load) (earth) will pump current in to Clouds (Source) during repetitive lightening strikes. Sudhakar Wasnik Phone. : 408-542-2928 From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Conway, Patrick R (Houston) Sent: Thursday, June 22, 2006 11:15 AM To: John Woodgate; emc-p...@ieee.org Subject: RE: [JunkMail] 1500 ohms 100 pF gun? <q> I wonder if Michael would explain how the discharge energy gets back >from the equipment being zapped to the source. It seems very mysterious. <q> Actually, not mysterious at all. But does require some thinking outside of what is considered "normal" current flow. A simple experiment (real or just a thought experiment) can show the answer. Try this experiment- run a normal ESD test for table top equipment. For this, doesn't matter what test standard. Must use a battery operated EUT. Make sure the EUT power cord is disconnected. Now discharge the ESD simulator to the EUT one time. Discharge works fine, no observable variance in the ESD. But, continue to zap the device. Notice that the observable characteristics of the ESD pulses become less severe. Smaller "pop" sound, plus the simulator tip has to get closer to the device to discharge. Eventually, you can no longer discharge to the EUT. So, what was happening? For all of those discharges what was the "Return path", since the EUT cord was removed? Why is it that the simulator no longer discharges? Those last two questions have the same answer. Maybe the normal loop model, "source-destination-return-to-source", does not apply? Hmm. Best Regards, Patrick Conway, NCE. 281.514.2259 281.524.5473 (fax) p.con...@hp.com - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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