EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: n4in on March 13, 2014, 02:54:13 am
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I just got a new ESD mat for the workbench and had the question, why is the snap clip ground cable that comes with the mat have a 1M ohm resistance in the ground cable?
Thanks,
David
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SO it discharges slowly.
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Yeah static voltage are high(er) voltages with little current capability. A 1 meg resistor is a non-event for discharing static voltages. Almost zero current flow = nearly zero voltage drop even across 1 meg. BUT... if the mat comes in contact with something live on your circuit board, like the power supply rails, that 1 meg resistor from the mat to ground prevents a short.
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Even for static shocks, the 1 meg resistor slows the discharge, which can help prevent damage to components. If you have a component with a residual charge on it, and you laid it on a low impedance ground, the rapid discharge could cause ESD damage.
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In the ESD mat that I got, the 1M is between the mat and my wrist, probably to protect me if I touch hot wire, not between the mat and the ground connection (the top layer of the mat is dissipative so no quick discharge anyway).
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The resistor is there to reduce the risk of electrocution... You really don't want have one wrist grounded (0 ohms) and then you accidentally touch live circuitry with your other hand... poof....
chers,
george.
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Thanks for the your responses, much appreciated.
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if 1M ohms is good, maybe infinite ohms is better?
there are so many 'cordless antistatic wrist straps' out there. they have 1Meg+infinite (lol) resistance. must be better, right?
(facepalm)
I'm so surprised that these thieves are allowed to continue selling. I see them on ebay and amazon and yet they never get shut down for fraud. 'corona effect' is what they claim, but it makes no sense at all.
as long as you run with a corded wrist strap that was properly built, it will work fine. I just wanted to mention the 'cordless ones' so that no one gets, uhm, 'burned'.
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if 1M ohms is good, maybe infinite ohms is better?
there are so many 'cordless antistatic wrist straps' out there. they have 1Meg+infinite (lol) resistance. must be better, right?
(facepalm)
I'm so surprised that these thieves are allowed to continue selling. I see them on ebay and amazon and yet they never get shut down for fraud. 'corona effect' is what they claim, but it makes no sense at all.
as long as you run with a corded wrist strap that was properly built, it will work fine. I just wanted to mention the 'cordless ones' so that no one gets, uhm, 'burned'.
Cordless antistatic wriststraps!
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if you have not seen them - and need a bit of a laugh - go to fleabay or amazon and you'll find plenty. read up on their claims of corona effect. but make sure you aren't in an office setting as you may laugh uncontrollably and bother those nearby ;)
I complained to amazon about these shucksters and yet they continue to be sold. someone is paying someone off, here, and it stinks! ;(
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if you have not seen them - and need a bit of a laugh - go to fleabay or amazon and you'll find plenty. read up on their claims of corona effect. but make sure you aren't in an office setting as you may laugh uncontrollably and bother those nearby ;)
I complained to amazon about these shucksters and yet they continue to be sold. someone is paying someone off, here, and it stinks! ;(
I just choked on my noodles.And best of all, people actually buy them