Re: [Elecraft] Radio Shack ESD mat doesn't meet spec
> I must be missing something in the test description. Wouldn't the > very low internal resistance of the Simpson voltmeter grossly swamp > the effects of the very high resistance of the mat? Yes. What is happening is that the capacitor is discharging through the meter in a millisecond or so. The meter needle jumps up only a small amount because of the damping in the meter movement. The only reason that technique works is that the absolute meter reading is not important, only the ratio of two readings. The meter jumped to about 1/10 scale when the capacitor was charged to 15V. So a few minutes later when the meter jumped to 1/20V, I deduced that the capacitor voltage must have been 7.5V. Alan N1AL On Sun, 2010-03-28 at 13:45 -0500, Mike Morrow wrote: > Gary Hvizdak wrote: > > > You can read the full text of Alan's post in the Reflector archives at > > http://mailman.qth.net/pipermail/elecraft/2008-February/083794.html > > Fred wrote: > > >Ingenious test set up Alan used to measure 1.0E10 ohms. > > I must be missing something in the test description. Wouldn't the > very low internal resistance of the Simpson voltmeter grossly swamp > the effects of the very high resistance of the mat? Even the input > resistance of a VTVM would be very low compared to the resistance > that is to be measured (even if measurement is only periodically > made on the circuit). > > Mike / KK5F > > > > __ > 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 __ 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
[Elecraft] Radio Shack ESD mat doesn't meet spec
Gary Hvizdak wrote: > You can read the full text of Alan's post in the Reflector archives at > http://mailman.qth.net/pipermail/elecraft/2008-February/083794.html Fred wrote: >Ingenious test set up Alan used to measure 1.0E10 ohms. I must be missing something in the test description. Wouldn't the very low internal resistance of the Simpson voltmeter grossly swamp the effects of the very high resistance of the mat? Even the input resistance of a VTVM would be very low compared to the resistance that is to be measured (even if measurement is only periodically made on the circuit). Mike / KK5F __ 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] Radio Shack ESD mat doesn't meet spec
Yes, I realize my measurement technique was not very accurate. For one thing, reading a meter flicker down around 10% of full scale is probably gives no better than +/-50% or so accuracy. But the Radio Shack anti-static mat was reading a couple orders of magnitude greater than the resistivity specified in the ANSI standard. A measurement error on the order of 50% doesn't matter. I have just ordered another anti-static mat from Digi-Key, a 2x3-foot desktop mat made by Desco, DK part number 16-1121-ND for $38.18. Unlike the Radio Shack product, this one has an actual data sheet where it states that it meets the ANSI spec. As a reality check I will try measuring it using the same technique I used before. If it also measures too high a resistance then I will conclude that there is something badly wrong with my measurement procedure. But if it reads OK, then I think we can safely assume the Radio Shack mat doesn't work as it should. Al N1AL On Fri, 2010-03-26 at 14:05 -0800, Rich wrote: > I have concerns about how that resistance was determined. I do not think the > methodology provides an accurate result. > First, look at eh schematic of the 260 - there are components in series > /parallel with the meter. Even with just the low current jack, there are > still components in series. > Second, I have never, NEVER, seen an analog meter provide accurate reading > of a peak or transient voltage. The frequency response/ transient response > is not there. Some of the components in parallel with the meter movement are > there to protect the meter. Additionally, there are balanced weights on the > mechanical portion of the movement to "stabilize" the movement and thus > decrease transient response. > When trying to calibrate a synchro system that was providing a sine wave of > about 20 Hz, my Simpson (freshly calibrated) was off by more than 20 %. of > the voltage displayed on an Oscilloscope which I was using for making the > adjustment. > Third, I know of no Simpson 260 that has a lowest range of 60 micro-amps, > everyone I know of is either 100 or 50 micro-amps. Don't knew what the new > ones are, but am sure that none of the old big ones have that value. > Here is a source for some info on the various Simpson meters. > http://simpson260.com/downloads/downloads.htm > > Rich > __ 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] Radio Shack ESD mat doesn't meet spec
I have concerns about how that resistance was determined. I do not think the methodology provides an accurate result. First, look at eh schematic of the 260 - there are components in series /parallel with the meter. Even with just the low current jack, there are still components in series. Second, I have never, NEVER, seen an analog meter provide accurate reading of a peak or transient voltage. The frequency response/ transient response is not there. Some of the components in parallel with the meter movement are there to protect the meter. Additionally, there are balanced weights on the mechanical portion of the movement to "stabilize" the movement and thus decrease transient response. When trying to calibrate a synchro system that was providing a sine wave of about 20 Hz, my Simpson (freshly calibrated) was off by more than 20 %. of the voltage displayed on an Oscilloscope which I was using for making the adjustment. Third, I know of no Simpson 260 that has a lowest range of 60 micro-amps, everyone I know of is either 100 or 50 micro-amps. Don't knew what the new ones are, but am sure that none of the old big ones have that value. Here is a source for some info on the various Simpson meters. http://simpson260.com/downloads/downloads.htm Rich -- View this message in context: http://n2.nabble.com/Re-Radio-Shack-ESD-mat-doesn-t-meet-spec-tp4799044p4806654.html Sent from the [K3] 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
Re: [Elecraft] Radio Shack ESD mat doesn't meet spec
Oh? I didn't know that. How's that work? Mike Brett Howard wrote: > The issue is that ESD often doesn't immediately kill components. More > often it simply shortens their lifespans. > > ~Brett (KC7OTG) > > > On Thu, 2010-03-25 at 20:59 -0400, Mike wrote: > >> My antecdoctal evidence says it worked for me, both on the initial build >> and on the removal and re-installation of the DSP board after upgrade. >> I'm not going to argue with what Alan said, as I'm not qualified, but >> I'm betting the health of my K3 on it, and wouldn't hesitate to pull it >> out again. YMMV. >> >> Perhaps Elecraft could publish what it considers to be minimum >> requirements, but I'd be willing to bet a cold 807 that because of >> liability issues, they'd go for the high-end specs. >> >> 73, Mike NF4L >> >> David Christ wrote: >> >>> So the question becomes does it work well enough for assembling >>> Elecraft kits even though it does not meet industry specs. Not >>> backing any particular horse in this race, but I know that there are >>> other areas in which industry specs are overkill for me. >>> >>> Who knows the answer? >>> >>> David K0LUM >>> >>> >>> >>> At 1:25 PM -0400 3/25/10, Gary Hvizdak wrote: >>> >>> All, With regard to the Radio Shack's 276-2370 "Anti-Static Service Kit", check out the message Alan Bloom (N1AL) posted a couple years ago which begins ... Well, I've convinced myself that the Radio Shack portable ESD mat, P/N 276-2370 doesn't work properly ... You can read the full text of Alan's post in the Reflector archives at http://mailman.qth.net/pipermail/elecraft/2008-February/083794.html 73, Gary KI4GGX __ 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 >>> __ >>> 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 >>> >>> >>> >> __ >> 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 >> > > > > __ 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] Radio Shack ESD mat doesn't meet spec
The issue is that ESD often doesn't immediately kill components. More often it simply shortens their lifespans. ~Brett (KC7OTG) On Thu, 2010-03-25 at 20:59 -0400, Mike wrote: > My antecdoctal evidence says it worked for me, both on the initial build > and on the removal and re-installation of the DSP board after upgrade. > I'm not going to argue with what Alan said, as I'm not qualified, but > I'm betting the health of my K3 on it, and wouldn't hesitate to pull it > out again. YMMV. > > Perhaps Elecraft could publish what it considers to be minimum > requirements, but I'd be willing to bet a cold 807 that because of > liability issues, they'd go for the high-end specs. > > 73, Mike NF4L > > David Christ wrote: > > So the question becomes does it work well enough for assembling > > Elecraft kits even though it does not meet industry specs. Not > > backing any particular horse in this race, but I know that there are > > other areas in which industry specs are overkill for me. > > > > Who knows the answer? > > > > David K0LUM > > > > > > > > At 1:25 PM -0400 3/25/10, Gary Hvizdak wrote: > > > >> All, > >> > >> With regard to the Radio Shack's 276-2370 "Anti-Static Service Kit", check > >> out the message Alan Bloom (N1AL) posted a couple years ago which begins > >> ... > >> > >> Well, I've convinced myself that the Radio Shack portable ESD mat, P/N > >> 276-2370 doesn't work properly ... > >> > >> You can read the full text of Alan's post in the Reflector archives at > >> http://mailman.qth.net/pipermail/elecraft/2008-February/083794.html > >> > >> 73, > >> Gary KI4GGX > >> > >> __ > >> 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 > >> > > > > __ > > 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 > > > > > > > __ > 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 __ 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] Radio Shack ESD mat doesn't meet spec
My antecdoctal evidence says it worked for me, both on the initial build and on the removal and re-installation of the DSP board after upgrade. I'm not going to argue with what Alan said, as I'm not qualified, but I'm betting the health of my K3 on it, and wouldn't hesitate to pull it out again. YMMV. Perhaps Elecraft could publish what it considers to be minimum requirements, but I'd be willing to bet a cold 807 that because of liability issues, they'd go for the high-end specs. 73, Mike NF4L David Christ wrote: > So the question becomes does it work well enough for assembling > Elecraft kits even though it does not meet industry specs. Not > backing any particular horse in this race, but I know that there are > other areas in which industry specs are overkill for me. > > Who knows the answer? > > David K0LUM > > > > At 1:25 PM -0400 3/25/10, Gary Hvizdak wrote: > >> All, >> >> With regard to the Radio Shack's 276-2370 "Anti-Static Service Kit", check >> out the message Alan Bloom (N1AL) posted a couple years ago which begins ... >> >> Well, I've convinced myself that the Radio Shack portable ESD mat, P/N >> 276-2370 doesn't work properly ... >> >> You can read the full text of Alan's post in the Reflector archives at >> http://mailman.qth.net/pipermail/elecraft/2008-February/083794.html >> >> 73, >> Gary KI4GGX >> >> __ >> 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 >> > > __ > 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 > > __ 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] Radio Shack ESD mat doesn't meet spec
If you have the Radio Shack mat, I recommend using it even though I'm not convinced it does a proper job of bleeding off static charge. For one thing, the anti-static wrist strap that comes with it does work. For another, even though it may not prevent static build up, at least it probably doesn't generate static charge itself as many plastics and other materials do. The proper procedures are important. Use a grounded soldering iron and connect the mat/wrist strap to the safety ground pin of a power socket. That ensures that you and the soldering iron are at the same potential. If in addition you are careful to always touch the chassis of the equipment or the ground/common of the PC board you are working on before you touch any circuitry (with your fingers or the soldering iron) then you should be safe. Alan N1AL On Thu, 2010-03-25 at 13:25 -0400, Gary Hvizdak wrote: > All, > > With regard to the Radio Shack's 276-2370 "Anti-Static Service Kit", check > out the message Alan Bloom (N1AL) posted a couple years ago which begins ... > > Well, I've convinced myself that the Radio Shack portable ESD mat, P/N > 276-2370 doesn't work properly ... > > You can read the full text of Alan's post in the Reflector archives at > http://mailman.qth.net/pipermail/elecraft/2008-February/083794.html > > 73, > Gary KI4GGX > > __ > 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 __ 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] Radio Shack ESD mat doesn't meet spec
Gary Hvizdak wrote: > All, > > With regard to the Radio Shack's 276-2370 "Anti-Static Service Kit", check > out the message Alan Bloom (N1AL) posted a couple years ago which begins ... > > Well, I've convinced myself that the Radio Shack portable ESD mat, P/N > 276-2370 doesn't work properly ... > > You can read the full text of Alan's post in the Reflector archives at > http://mailman.qth.net/pipermail/elecraft/2008-February/083794.html Ingenious test set up Alan used to measure 1.0E10 ohms. Fred K6DGW __ 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] Radio Shack ESD mat doesn't meet spec
David, I was the one that brought this mat up (unfortunately), and all I can say is that it was fine for putting my K3 together very successfully and I'll use it again. I'll stop there, but will add that any time I like, after walking across my floor here, I can draw a spark from metal objects. While building my kit, I followed Don's suggestions to the letter, always putting on the wrist strap before beginning and touching the mat before any parts or tools and grounded the "system" through the mains ground in my shack (tied to shack ground too, of course). As always, one should weigh evidence and do what they see as the solution. 73, and I'll go back into my cave, Don, WB5HAK __ 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] Radio Shack ESD mat doesn't meet spec
So the question becomes does it work well enough for assembling Elecraft kits even though it does not meet industry specs. Not backing any particular horse in this race, but I know that there are other areas in which industry specs are overkill for me. Who knows the answer? David K0LUM At 1:25 PM -0400 3/25/10, Gary Hvizdak wrote: >All, > >With regard to the Radio Shack's 276-2370 "Anti-Static Service Kit", check >out the message Alan Bloom (N1AL) posted a couple years ago which begins ... > >Well, I've convinced myself that the Radio Shack portable ESD mat, P/N >276-2370 doesn't work properly ... > >You can read the full text of Alan's post in the Reflector archives at >http://mailman.qth.net/pipermail/elecraft/2008-February/083794.html > >73, >Gary KI4GGX > >__ >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 __ 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] Radio Shack ESD mat doesn't meet spec
All, With regard to the Radio Shack's 276-2370 "Anti-Static Service Kit", check out the message Alan Bloom (N1AL) posted a couple years ago which begins ... Well, I've convinced myself that the Radio Shack portable ESD mat, P/N 276-2370 doesn't work properly ... You can read the full text of Alan's post in the Reflector archives at http://mailman.qth.net/pipermail/elecraft/2008-February/083794.html 73, Gary KI4GGX __ 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] Radio Shack ESD mat doesn't meet spec
On Wed, 2008-02-27 at 19:23, [EMAIL PROTECTED] wrote: > In a message dated 2/27/2008 9:54:12 A.M. Pacific Standard Time, > [EMAIL PROTECTED] writes: > Well, I've convinced myself that the Radio Shack portable ESD mat, P/N > 276-2370 doesn't work properly. > > Al N1AL > > > ___ > Did the test standard you used tell you what the test device voltages should > be. Yes, they specify it be tested with both 10V and 100V. I used 15V for my test since that was convenient. > Also, most Static dissipative mats have a texture which can > significantly reduce the actual surface contact area affecting the readings > considerably. > I still think the best way to test is to fabricate a simple electrometer > and connect the sensor (after charging) to the surface through contact. That's basically what I did. I used electrodes similar to the standard ones specified in the standard. > One big point - Mats do age and > dry out becoming useless in a matter of a few years. Dry out? You mean they are wet? :=) Al N1AL ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Radio Shack ESD mat doesn't meet spec
In a message dated 2/27/2008 9:54:12 A.M. Pacific Standard Time, [EMAIL PROTECTED] writes: Well, I've convinced myself that the Radio Shack portable ESD mat, P/N 276-2370 doesn't work properly. The "ESD Association" http://www.esda.org has promulgated an industry-standard test for ESD mats, ESD S4.1. It is the standard specified by most commercial mats. I decided not to spring for the $70 to buy a copy of the standard, but other information I found on the web describes the test in general terms. It uses two circular electrodes, each weighted with 5 pounds, spaced 10 inches apart on the mat. The "Point to Point Resistance" is specified to be: At 40-60% RH: 10^6 - 10^7 ohms At 20-40% RH: 10^7 - 10^8 ohms At 10-20% RH: 10^8 - 10^9 ohms I don't know what the RH here in Santa Rosa was yesterday when I did the test, but I don't think it was very low since it has been raining recently and the ground is still damp. For sure the resistance shouldn't be below 10^9 ohms (1 gigohm) and probably more like 10^8 or 10^7 (100 or 10 megohms). I measured 2.5 x 10^10 ohms (25 gigohms), which puts the Radio Shack mat way out of spec. Test procedure: I didn't find a specification on the electrode size, but in the photo of a popular tester they look to be maybe 3 or 4 inches in diameter. For my test, the electrodes were two saucepans, each about 7 inches in diameter and weighted with 5 pounds. They were spaced 10 inches apart on the mat (3 inches edge-to-edge). I connected a 0.1 uF film capacitor between the two pans and charged it to 15V with a power supply. I set my ancient Simpson analog volt-ohm meter to 60 uA full scale. If I touch the leads across the capacitor immediately after charging, the needle momentarily jumps to about 6 uA (1/10 full scale) as the capacitor discharges through the meter. If I wait half an hour (1800 seconds) for the capacitor to partially discharge through the mat resistance, the needle jumps to about 3 uA. An R-C network discharges to 3/6 of original voltage in about 0.7 time constant. So the time constant must be 1800/0.7 = 2571 seconds. That implies the mat resistance is 2571 sec / 0.1 uF ~= 2.5 x 10^10 ohms. Al N1AL ___ Did the test standard you used tell you what the test device voltages should be. Also, most Static dissipative mats have a texture which can significantly reduce the actual surface contact area affecting the readings considerably. I still think the best way to test is to fabricate a simple electrometer and connect the sensor (after charging) to the surface through contact. That will tell you very quickly if it is working. Point to this is the voltage of a transistor amplified Ohmmeter is very low these days. A standard VOM is usually 1.5 volts and many FET DVM is much lower because they are also used to test semiconductors and capacitors. ESD that is damaging is at least a few hundred volts. Most ESD workstations are certified to 1000 volts or more. Don't throw out the RS mat yet. The highest quality mil spec'd mats may cost you a lot more and not buy you anything. One big point - Mats do age and dry out becoming useless in a matter of a few years. Al WA6VNN **Ideas to please picky eaters. Watch video on AOL Living. (http://living.aol.com/video/how-to-please-your-picky-eater/rachel-campos-duffy/ 2050827?NCID=aolcmp0030002598) ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
[Elecraft] Radio Shack ESD mat doesn't meet spec
Well, I've convinced myself that the Radio Shack portable ESD mat, P/N 276-2370 doesn't work properly. The "ESD Association" http://www.esda.org has promulgated an industry-standard test for ESD mats, ESD S4.1. It is the standard specified by most commercial mats. I decided not to spring for the $70 to buy a copy of the standard, but other information I found on the web describes the test in general terms. It uses two circular electrodes, each weighted with 5 pounds, spaced 10 inches apart on the mat. The "Point to Point Resistance" is specified to be: At 40-60% RH: 10^6 - 10^7 ohms At 20-40% RH: 10^7 - 10^8 ohms At 10-20% RH: 10^8 - 10^9 ohms I don't know what the RH here in Santa Rosa was yesterday when I did the test, but I don't think it was very low since it has been raining recently and the ground is still damp. For sure the resistance shouldn't be below 10^9 ohms (1 gigohm) and probably more like 10^8 or 10^7 (100 or 10 megohms). I measured 2.5 x 10^10 ohms (25 gigohms), which puts the Radio Shack mat way out of spec. Test procedure: I didn't find a specification on the electrode size, but in the photo of a popular tester they look to be maybe 3 or 4 inches in diameter. For my test, the electrodes were two saucepans, each about 7 inches in diameter and weighted with 5 pounds. They were spaced 10 inches apart on the mat (3 inches edge-to-edge). I connected a 0.1 uF film capacitor between the two pans and charged it to 15V with a power supply. I set my ancient Simpson analog volt-ohm meter to 60 uA full scale. If I touch the leads across the capacitor immediately after charging, the needle momentarily jumps to about 6 uA (1/10 full scale) as the capacitor discharges through the meter. If I wait half an hour (1800 seconds) for the capacitor to partially discharge through the mat resistance, the needle jumps to about 3 uA. An R-C network discharges to 3/6 of original voltage in about 0.7 time constant. So the time constant must be 1800/0.7 = 2571 seconds. That implies the mat resistance is 2571 sec / 0.1 uF ~= 2.5 x 10^10 ohms. Al N1AL ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
