Aw, gee Alan. 1) Plus or minus 10% of say 10 Megohms simply means between 9 and 11 Meghoms. No negative resistance is implied or needed (but if you find one you'll be rich and famous!)
2) A solidus is commonly used in place of "per" so I read that as the resistance between two electrodes a certain distance apart. That said, Alan did the evaluation of a several AS mats that led to the list I used in many Elecraft manuals because, as he found, many mats are virtually useless for dissipating static. Here's the list Alan developed that we recommend: >> U-line (Model 12743 specified at 107 ohms) >> Desco (Model 66164, specified at 106 to 108 ohms) >> 3MTM Portable Service Kit (Model 8505 or 8507, specified at 106 to 109 >> ohms) 73, Ron AC7AC -----Original Message----- From: Elecraft [mailto:[email protected]] On Behalf Of Alan Bloom Sent: Sunday, April 17, 2016 5:10 PM To: [email protected] Subject: Re: [Elecraft] Velleman AS9 mat for KX3 I'm suspicious. Why are some resistances specified "+/-"? I'm pretty sure it doesn't have a negative resistance. And the units of volume resistivity are ohm-cm (or ohm-m), not ohm/cm. The fact that it doesn't specify compliance to any industry standard also is a concern. An anti-static mat should comply with "ANSI/ESD S4.1" or "ANSI/ESD S20.20". Those standards specify measuring the resistance between two weighted, circular electrodes of a certain size and spaced a certain distance apart on the mat. The resistance should measure between 1 Mohm and 1 Gohm, depending on the relative humidity. Here are the results of some testing I did on anti-static mats a few years ago, along with a recommendation for one mat I found that did measure within spec: http://www.mail-archive.com/elecraft%40mailman.qth.net/msg94407.html The bottom line is, many so-called "anti-static" mats don't do the job. And the problem is, there is no easy way to tell. Just because you managed to build something without damaging any parts doesn't prove the mat is working correctly. This is one area where it doesn't pay to go cheap. Alan N1AL On 04/17/2016 01:24 PM, Bruce Nourish wrote: > Hi folks, > > I'm adding a 2m unit to my factory built KX3, and wanted to check if > the specs on this mat were adequate: > > http://www.velleman.eu/products/view/?country=be&lang=en&id=382422 > > surface resistance: ± 10^8 - 10^10 Ω/sq volume resistance: < 10^10 > Ω/cm RTT (point to point): ± 10^8 - 10^10 Ω > > It includes a wrist strap with a 1 MΩ resistor. The numbers look to be > in the ball park of the examples given in the KX3 manual, but I wanted > to check before I started poking around the guts of my very expensive toy. > > Bruce ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
