Re: [Elecraft] Anti Static Mats
On 04/13/2014 04:54 PM, Fred Townsend wrote: > The argument has been made that when a high voltage charge it > is discharged through the mat that the discharge must not be > too fast nor too slow. It must be just right. To Goldilocks > and her followers I say no it’s not so. Not "just right" but within an acceptable range. > A RC of 47 ohms and 1500 pf is often used to model the human body. The human body model I am familiar with is 100 pf / 1500 ohms http://en.wikipedia.org/wiki/Human_body_model . If the human body is charged to 10kV, then when when you touch something grounded a current of 6.7A flows for 150 ns. That's too short a time to injure you but definitely enough to wake you up. If you are holding an electronic device and touch it to something grounded then that current will flow through the device. That's why you really don't want to use a metal plate in place of an anti-static mat. The mat has a high resistance in order to limit the current from an electro-static discharge. Even if the metal plate is not grounded directly it still has some capacitance to ground. Assuming, let's say, 10 pF then you still get 6.7A but it flows for only 15 ns. That's still more than enough to destroy a sensitive electronic device. So you don't want the mat resistance to be too low. If the mat resistance is too high, then it can't perform its other task of equalizing the voltage on all the devices placed on the mat (and the body of the operator, connected through the wrist strap). So yes, the mat resistance needs to be within a certain range. That is why industry standards have been created to specify that. Alan N1AL __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Anti Static Mats
Don, if you mean by ‘developed’ a charge is generated then no, the triboelectric effect doesn’t work that way. See http://en.wikipedia.org/wiki/Triboelectric_effect. If you mean the previously, developed by friction on the body, charge is transferred then yes, but then in only in a very limited way. A RC of 47 ohms and 1500 pf is often used to model the human body. The charge transferred will be in proportion to the surface capacity of the touched object. Small objects tend to have a very small surface capacity so little or no charge is transferred. Back to the subject at hand. What part do the antistatic mats play? The argument Alan seems to make is there is an optimal resistance for the anti-static mat and that is critical to maintain the mat within that range. To that I say the Emperor has no clothes. There are really two issues here. 1. How do I prevent static from being developed in the first place? 2. How is a developed charge going to hurt my component? With regard to mats, just about any soft rubber mat will not react to the triboelectric effect so it is passes item 1 above. Hard rubber, plastic or other dielectric materials such as Formica or Varathane tabletops are questionable. With regard to item 2) components are damaged when either their dielectric limits or their current carrying capacity are exceeded. By definition antistatic mats do not build up a charge so exceeding dielectric limits seems improvable and so that brings us down to exceeding current limits. The argument has been made that when a high voltage charge it is discharged through the mat that the discharge must not be too fast nor too slow. It must be just right. To Goldilocks and her followers I say no it’s not so. I think a proof here is beyond the scope of this forum. However, an examination of the human body model (47 ohms and 1500 pf) will easily lead to that proof. For those still not convinced I offer this except from the first TI data sheet I picked up. It states: “ESD Protection Exceeds JESD 22”. Yes there is a manufacture’s requirement for antistatic endurance. If they don’t exceed JESD22, then special packaging and markings are required. You’ll know to take extra special precautions when you see the labels. 73 Fred, AE6QL -Original Message- >From: Don Wilhelm >Sent: Apr 7, 2014 10:37 PM >To: elecraft@mailman.qth.net >Subject: Re: [Elecraft] Anti Static Mats > >When one touches it, a charge is developed - then when it comes in >contact with a fully conducting surface, damage can occur. If instead >you are working on a proper anti-static mat, the charge from your body >and the part is dissipated slowly, no damage will be done and everything >will be at the same potential. > >73, >Don W3FPR > >On 4/8/2014 12:47 AM, Fred Townsend wrote: >> That would mean the part was charged. How would that happen? >> >> __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Anti Static Mats
http://en.wikipedia.org/wiki/Antistatic_agent - Chuck, KE9UW -- View this message in context: http://elecraft.365791.n2.nabble.com/Anti-Static-Mats-tp7586727p7587021.html Sent from the Elecraft mailing list archive at Nabble.com. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Anti Static Mats
Hard to figure out what he is trying to prove. Finally on the antistatic mat issue, his point was that it doesn't affect measurements made with circuits lying on the mat. I guess I was thinking that he would show us how the mat is antistatic, as he did with the bags. Greetings, all. Dave Jones, who runs the EEVblog, has a few videos relating to anti-static bags and mats. The first one that talks about anti-static bags is worth watching. It shows the difference between the common pink anti-static bags and the silvery static shielding bags. Those pink bags and the related "anti-static" chip carriers don't do as much to protect your components as you might think. http://www.eevblog.com/2012/02/25/eevblog-247-anti-static-bag-myth-revisted/ http://www.eevblog.com/2012/03/01/eevblog-250-anti-static-mat-myth/ http://www.eevblog.com/2014/03/02/eevblog-585-lab-bench-esd-matting-upgrade-tagarno-hd-microscope/ The first part of the third video (mainly starting around 2.5 minutes in) talks about ESD matting that Dave was putting down on his lab benches. -- Cheers! Kevin. http://www.ve3syb.ca/ |"Nerds make the shiny things that distract Owner of Elecraft K2 #2172 | the mouth-breathers, and that's why we're | powerful!" #include| --Chris Hardwick - Chuck, KE9UW -- View this message in context: http://elecraft.365791.n2.nabble.com/Anti-Static-Mats-tp7586727p7586918.html Sent from the Elecraft mailing list archive at Nabble.com. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Anti Static Mats
Greetings, all. Dave Jones, who runs the EEVblog, has a few videos relating to anti-static bags and mats. The first one that talks about anti-static bags is worth watching. It shows the difference between the common pink anti-static bags and the silvery static shielding bags. Those pink bags and the related "anti-static" chip carriers don't do as much to protect your components as you might think. http://www.eevblog.com/2012/02/25/eevblog-247-anti-static-bag-myth-revisted/ http://www.eevblog.com/2012/03/01/eevblog-250-anti-static-mat-myth/ http://www.eevblog.com/2014/03/02/eevblog-585-lab-bench-esd-matting-upgrade-tagarno-hd-microscope/ The first part of the third video (mainly starting around 2.5 minutes in) talks about ESD matting that Dave was putting down on his lab benches. -- Cheers! Kevin. http://www.ve3syb.ca/ |"Nerds make the shiny things that distract Owner of Elecraft K2 #2172 | the mouth-breathers, and that's why we're | powerful!" #include | --Chris Hardwick __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Anti Static Mats
When one touches it, a charge is developed - then when it comes in contact with a fully conducting surface, damage can occur. If instead you are working on a proper anti-static mat, the charge from your body and the part is dissipated slowly, no damage will be done and everything will be at the same potential. 73, Don W3FPR On 4/8/2014 12:47 AM, Fred Townsend wrote: That would mean the part was charged. How would that happen? __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Anti Static Mats
The human body can store quite a bit of charge. When you lay a part on a conductive surface, charge flows between your body and the surface, through the part. That's why (if you don't have an anti-static mat and wrist strap) you should always touch the chassis, PC board, whatever with your other hand before placing a part on it. Alan N1AL On 04/07/2014 09:47 PM, Fred Townsend wrote: That would mean the part was charged. How would that happen? -Original Message- From: "Lawrence D. Lopez" Sent: Apr 7, 2014 5:23 AM To: Alan Bloom Cc: elecraft@mailman.qth.net Subject: Re: [Elecraft] Anti Static Mats if you put a sensitive part on a something that conducts well then you get a static discharge and damage. __ __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Anti Static Mats
That would mean the part was charged. How would that happen? -Original Message- >From: "Lawrence D. Lopez" >Sent: Apr 7, 2014 5:23 AM >To: Alan Bloom >Cc: elecraft@mailman.qth.net >Subject: Re: [Elecraft] Anti Static Mats > >if you put a sensitive part >on a something that conducts >well then you get a static >discharge and damage. >__ __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Anti Static Mats
If I got such an answer from a fire department, I would tell them that the dead cat may well be hidden in the tree, and once dead would likely attract nature's sanitation team and they would likely remove the dead cat with at least as much efficiency as the fire department can muster. If the cat is injured, it may need help that it can not provide for it's self. I'm not a cat lover, I just don't think this analogy is worth much. (And, not trying to start a budget discussion--I would not call the fire department, but a five-year old kid might). A bad anti-static mat may relate more to the sick cat than the dead cat. When you pull on the tail of the sick cat you may get a weak mew that may eventually go silent, returning this thread back to radio through reference to an old wireless metaphor. YMMD Richard Hill On 4/6/2014 10:16 PM, Fred Townsend wrote: Alan if you call the fire department about a cat up a tree they will ask if you have ever seen a dead cat in a tree inferring that the cat will find its own way down from the tree without help. If the resistance and maintenance of the mat are so critical don't you think we would reports of dead mats by now? 73 Fred, AE6QL -Original Message- From: Fred Townsend Sent: Apr 6, 2014 9:24 PM To: Sam Morgan , elecraft@mailman.qth.net Subject: Re: [Elecraft] Anti Static Mats I was once asked if the mats on my assembly line were antistatic. I thought they were but I wasn’t sure since I didn’t buy them. The mats took a beating and only lasted a year or two. Some were new and some were in tatters. I flipped over a new mat. It clearly said antistatic but the older mats didn’t have any labels and they looked different. I took an ohmmeter, stabbing the probes in about an inch apart. No reading. No reading for the new mats or the antistatic bags we used by the thousands. After rubbing with fur, a triboelectric meter (a meter used for measuring static charge) was used on the mats and bags without measuring a charge. My conclusion was surfaces could be antistatic without measuring any resistance. Same for bags. If you have one from your Elecraft kit, try measuring it with an ohmmeter. 73 Fred, AE6QL -Original Message- From: Sam Morgan Sent: Apr 6, 2014 7:21 PM To: elecraft@mailman.qth.net Subject: Re: [Elecraft] Anti Static Mats oops never mind, I just reread the pdf on the Sierra FS and it's made in China, where as the Desco is made in the US (or so they say) On 4/6/2014 9:00 PM, Alan Bloom wrote: I recommend against using a mat that has no specifications other than asserting it is an "anti-static mat." I found that the two I bought and tested both had too high a resistance to do any good. -- GB & 73 K5OAI Sam Morgan __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to reh...@ix.netcom.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Anti Static Mats
if you put a sensitive part on a something that conducts well then you get a static discharge and damage. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Anti Static Mats
Alan if you call the fire department about a cat up a tree they will ask if you have ever seen a dead cat in a tree inferring that the cat will find its own way down from the tree without help. If the resistance and maintenance of the mat are so critical don't you think we would reports of dead mats by now? 73 Fred, AE6QL -Original Message- >From: Fred Townsend >Sent: Apr 6, 2014 9:24 PM >To: Sam Morgan , elecraft@mailman.qth.net >Subject: Re: [Elecraft] Anti Static Mats > > >I was once asked if the mats on my assembly line were antistatic. I thought >they were but I wasn’t sure since I didn’t buy them. The mats took a beating >and only lasted a year or two. Some were new and some were in tatters. I >flipped over a new mat. It clearly said antistatic but the older mats didn’t >have any labels and they looked different. I took an ohmmeter, stabbing the >probes in about an inch apart. No reading. No reading for the new mats or the >antistatic bags we used by the thousands. After rubbing with fur, a >triboelectric meter (a meter used for measuring static charge) was used on the >mats and bags without measuring a charge. > >My conclusion was surfaces could be antistatic without measuring any >resistance. Same for bags. If you have one from your Elecraft kit, try >measuring it with an ohmmeter. >73 >Fred, AE6QL > > >-Original Message- >>From: Sam Morgan >>Sent: Apr 6, 2014 7:21 PM >>To: elecraft@mailman.qth.net >>Subject: Re: [Elecraft] Anti Static Mats >> >>oops never mind, I just reread the pdf on the Sierra FS and it's made in >>China, where as the Desco is made in the US (or so they say) >> >>On 4/6/2014 9:00 PM, Alan Bloom wrote: >> >>> I recommend against using a mat that has no specifications other than >>> asserting it is an "anti-static mat." I found that the two I bought and >>> tested both had too high a resistance to do any good. >> >>-- >>GB & 73 >>K5OAI >>Sam Morgan > __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Anti Static Mats
On 04/06/2014 09:24 PM, Fred Townsend wrote: ...I flipped over a new mat. It clearly said antistatic but the > older mats didn’t have any labels and they looked different. > I took an ohmmeter, stabbing the probes in about an inch apart. > No reading. You can't measure the mat resistance with an ohm meter. Or to be more accurate, if you get a reading on the meter, then the resistance is way too low. The resistance between a pair of meter probes would typically be in the range of 100's of megohms or more, which is too high to measure with a multimeter. At the bottom of this message is a description of the test procedure I used: http://www.mail-archive.com/elecraft%40mailman.qth.net/msg94407.html Alan N1AL __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Anti Static Mats
I was once asked if the mats on my assembly line were antistatic. I thought they were but I wasn’t sure since I didn’t buy them. The mats took a beating and only lasted a year or two. Some were new and some were in tatters. I flipped over a new mat. It clearly said antistatic but the older mats didn’t have any labels and they looked different. I took an ohmmeter, stabbing the probes in about an inch apart. No reading. No reading for the new mats or the antistatic bags we used by the thousands. After rubbing with fur, a triboelectric meter (a meter used for measuring static charge) was used on the mats and bags without measuring a charge. My conclusion was surfaces could be antistatic without measuring any resistance. Same for bags. If you have one from your Elecraft kit, try measuring it with an ohmmeter. 73 Fred, AE6QL -Original Message- >From: Sam Morgan >Sent: Apr 6, 2014 7:21 PM >To: elecraft@mailman.qth.net >Subject: Re: [Elecraft] Anti Static Mats > >oops never mind, I just reread the pdf on the Sierra FS and it's made in >China, where as the Desco is made in the US (or so they say) > >On 4/6/2014 9:00 PM, Alan Bloom wrote: > >> I recommend against using a mat that has no specifications other than >> asserting it is an "anti-static mat." I found that the two I bought and >> tested both had too high a resistance to do any good. > >-- >GB & 73 >K5OAI >Sam Morgan __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Anti Static Mats
oops never mind, I just reread the pdf on the Sierra FS and it's made in China, where as the Desco is made in the US (or so they say) On 4/6/2014 9:00 PM, Alan Bloom wrote: I recommend against using a mat that has no specifications other than asserting it is an "anti-static mat." I found that the two I bought and tested both had too high a resistance to do any good. -- GB & 73 K5OAI Sam Morgan __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Anti Static Mats
On 04/06/2014 01:10 PM, Sam Morgan wrote: Due to the recent subject of Anti Static mats, I did a little googling and thought I'd share my findings. ... maybe Alan or someone more knowledgeable than I can let us know if the Sierra is really up to the standards we need met? From my 2010 posting http://www.mail-archive.com/elecraft%40mailman.qth.net/msg94407.html "So my recommendation is to buy a mat such as the Desco model that has a data sheet that specifies that it meets ANSI/ESD S4.1 or ANSI/ESD S20.20." I recommend against using a mat that has no specifications other than asserting it is an "anti-static mat." I found that the two I bought and tested both had too high a resistance to do any good. === On 04/06/2014 02:20 PM, Lynn W. Taylor, WB6UUT wrote: > One thing worth noting: 1000x lower resistance isn't necessarily > better, Right, you don't want the mat to be too low a resistance either. Do not substitute a metal sheet for an anti-static mat. That just makes it even more likely you will zap something. === On 04/06/2014 01:43 PM, Larry Lopez wrote: > They made me take an ESD course at work and well I have a few > comments I feel forced to make. Larry had a number of good points, for example: > When you have a discharge you might have failures months or years > later. It may be damaged and it may work fine. > > For a while. Exactly right. ESD is insidious. People think that if you didn't feel a "zap" when you touch something that there was no electro-static discharge. But a discharge that you can't feel can still be enough to damage a sensitive part. === On 04/06/2014 12:10 PM, Fred Townsend wrote: ... > As a consultant I have done ESD audits of factories. If they know > the audit is coming all the wrist straps are in place. Surprise > audits are another thing. I find the straps and footwear to be > rarely used. How can they get away with that? The answer is they > have good work habits that avoid ESD problems rather than bleeding > off static build up. I think in many cases they actually are not getting away with it as well as they think. Part failures happen for a reason. If the reason can't be found it could well have been ESD. Some factories do in fact strictly enforce static-safe procedures. HP/Agilent "got religion" on this many years ago, at least here in Sonoma County CA. > Here are a few everyday hints the pros use. > 1. Wear cotton! ... [etc. etc.] All those suggestions can help, but they are not foolproof. It requires constant vigilance to make sure you don't make a mistake. Rather than go to all that trouble, why not just use the anti-static mat and wrist strap and be done with it? If the wrist strap is too awkward, an ankle strap is a good alternative. Alan N1AL __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Anti Static Mats
One thing worth noting: 1000x lower resistance isn't necessarily better, especially given that it's not uncommon to have a battery in modern gear. The mat isn't supposed to ground everything, it's supposed to bleed off static charges. It's also why wrist straps or something to ground you are good, but should have several mega ohms of resistance -- you don't want to touch something that has some voltage on it and complete a low-impedance circuit to ground. Just FWIW. 73 -- Lynn On 4/6/2014 1:10 PM, Sam Morgan wrote: Here are the results: Radio Shack P/N 276-2370 ($22.99) - 26 G ohms (26,000 M ohms) Jameco P/N 10584 ($16.45) - 44 G ohms (44,000 M ohms) Digi-Key P/N 16-1121-ND, (Desco 66164) ($38.18) - 41 M ohms The Desco mat's resistance is about 1000x lower than the cheaper ones! __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Anti-Static Mats
Ron D'Eau Claire wrote: >Ian, if you read my message you'll find that we agree on all but one point. > Having re-read the whole of the ESD section in the K3 Assembly Manual, I wouldn't disagree with a single word. But each of us is now trying to condense this whole subject into an exchange of brief e-mail messages. That's a mistake, so let us go no further down that road. My parting words are to urge everyone to read what Wayne and Ron wrote about ESD on pages 3-4 of the Assembly Manual. Then think very seriously about investing in a mat and wrist strap, to protect our much larger investment in the K3. -- 73 from Ian GM3SEK http://www.ifwtech.co.uk/g3sek __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] Anti-Static Mats
snip ...> > When doing field repair we seldom have the luxury of anti-static mats, > wrist > straps, etc., but a little care in what we set the board on (not on cloth, > etc.) and touching a ground before picking them up keeps the parts safe. > > Ron AC7AC > We did the touch method for some time before we got the portable mats, BUT, you can watch somebody and catch them repeatedly not doing the touch every time they make contact with the machine. It CAN be learned but it takes some diligence and commitment. Portable mat kits come folded up in a pouch, have the wrist strap and cables included and fit easily inside your tool kit. This was over 10 years ago at least, maybe 15. I still have mine (and a spares and extra straps) and that is what I use today. Retired 8+ years ago. We used static mats and wrist straps for service calls and anytime we connected or disconnected a cable or opened the case the strap was required. If we removed anything, the mat was to be used. We were also required to carry a log sheet available to show to anybody (leaders had to check them randomly) showing we measured and recorded the resistance the 1 meg resister in the wrist strap monthly! A real pain for the leaders who also had to carry the pack and the check was the most use the pouch received. 73, de Jim KG0KP __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] Anti-Static Mats
Ian, if you read my message you'll find that we agree on all but one point. You added some good information about ESD safety, but that wasn't the intent of the post. I was responding to a specific comment about someone "touching" an ESD mat to discharge oneself. As you know, that won't work. (Actually the person who wrote that knows that too. He's an experienced tech. It was just a poor choice of words.) But not everyone knows that. Indeed, a while back we had a thread started by people who decided they had defective "anti-static" mats because placing their DMM probes on them didn't show a low-resistance across the mat. That's not how static-dissipating mats work. You wrote "The wrist strap is not 'optional'" You can work without a wrist strap if you regularly touch a good ground to discharge yourself safely. That has the same effect as bleeding off the charge through a wrist strap. I and countless others have done it for decades and I'm sure that's why Wayne called for the "touch a ground" option to be included in the manuals. However, we're not saying to touch a ground once, but before every time you pick up a sensitive part, squirm in your seat, etc. The worker must keep a significant charge from accumulating on his/her body. Smart companies require wrist straps on the work benches because it's easy to forget to touch the ground. One zapped board buys a whole lot of wrist straps. When doing field repair we seldom have the luxury of anti-static mats, wrist straps, etc., but a little care in what we set the board on (not on cloth, etc.) and touching a ground before picking them up keeps the parts safe. Ron AC7AC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] Anti-Static Mats
Ron D'Eau Claire wrote: >Greg K2UM wrote: >One touch and no static sparks to my equipment during operation, especially >during the winter, and a whole desk mat to work on my K3s and other >equipment. > >- > >If you want to discharge the static with a "touch" you need to touch a real, >bare-metal ground. Those mats do not provide a "ground" but rather merely >dissipate static charges as they accumulate. Sorry, that isn't correct. ESD protection is NOT simply about connecting things to "ground". Grounding has some part to play, but it's missing the main point. Remember, it isn't the static charge that does the damage - it's the DIScharge! A sudden direct discharge creates a large pulse of current which can be very damaging, and can also induce damaging voltages and currents in surprisingly distant locations. That is why ESD mats are deliberately designed to PREVENT a sudden discharge to ground! By having a large built-in resistance they force static charges to dissipate quite slowly, over timescales of seconds. >Sure, if you hold your hand on >one and don't move for several minutes, you should be discharged too, but a >"touch" won't do it as evidenced by a simple check with an ohmmeter. Almost >no DMM will indicate anything but an "open circuit" when the probes are both >touched to the mat. > That much is correct - Greg is being optimistic that literally "one touch" to the ESD mat will be enough to remove the static charge on his whole body. That's what the wrist strap is for. >Optionally you can discharge yourself with a wrist strap that has a >metal-to-you contact through a 1 Megohm resistor to ground. The 1 Megohm is >adequate to rapidly discharge your body while limiting any accidental >currents from touching circuit to a safe level. The main advantage of the >wrist strap is that you don't need to remember to keep touching a ground. >It'll take care of any static charge you accumulate as it builds, and your >mat will keep dissipating any static charges on the equipment you lay on it. > The wrist strap is not "optional". Your own body is the largest charge carrier around, and it needs to be kept at the same potential as the equipment sitting on the ESD mat. When we're wearing a wrist strap, it is working for us all the time - not just when we remember to touch something. Also the 1M resistors are not optional - they allow static charges to be dissipated over timescales of a few seconds, but 1M is high enough to avoid the risk of electric shock from the equipment we're working on. NEVER ground yourself with a strap that can't be pulled off and doesn't contain a safety resistor. Those are the reasons why all ESD mats and wrist straps are made precisely the way they are (including the pop studs) and not any other way. > >When I sit down at the bench to work, I first touch a bare metal ground, don >the wrist strap and set to work with the parts and boards on the static >dissipating mat. > The main point is that the ESD mat and the wrist strap are bonded together, so that everything in your ESD-safe zone is at the same potential. Having done that, then you can start to think about "grounding". To make sure that the any external connections you bring into the ESD-safe zone, such as the soldering iron and ground-connected test probes, are also at the same potential, the whole setup needs to be bonded to the electrical supply ground. That is: wrist strap (including 1M resistor) connected to the stud at the corner of the ESD mat. That stud is then directly connected to the mains ground bus for the whole workbench. So the principles are - in the following order: 1. Keep everything in your ESD-safe zone at the same potential. 2. Use a purpose-made ESD mat and ESD wrist strap (with the 1M resistor) to make sure that any static charges dissipate GENTLY. 3. Having done 1 and 2, also bond your ESD-safe zone to the electrical ground. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] Anti-Static Mats
Greg K2UM wrote: One touch and no static sparks to my equipment during operation, especially during the winter, and a whole desk mat to work on my K3s and other equipment. - If you want to discharge the static with a "touch" you need to touch a real, bare-metal ground. Those mats do not provide a "ground" but rather merely dissipate static charges as they accumulate. Sure, if you hold your hand on one and don't move for several minutes, you should be discharged too, but a "touch" won't do it as evidenced by a simple check with an ohmmeter. Almost no DMM will indicate anything but an "open circuit" when the probes are both touched to the mat. Optionally you can discharge yourself with a wrist strap that has a metal-to-you contact through a 1 Megohm resistor to ground. The 1 Megohm is adequate to rapidly discharge your body while limiting any accidental currents from touching circuit to a safe level. The main advantage of the wrist strap is that you don't need to remember to keep touching a ground. It'll take care of any static charge you accumulate as it builds, and your mat will keep dissipating any static charges on the equipment you lay on it. When I sit down at the bench to work, I first touch a bare metal ground, don the wrist strap and set to work with the parts and boards on the static dissipating mat. Ron AC7AC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
