Rats. And here I thought I'd found a good solution to my problem...
I work in a research lab with lots of somewhat touchy equipment. It
also happens to be in central Iowa, USA, which is about as arid as the
Gobi desert this time of year, so as you can imagine, everyone is a real
live walking talking Van DeGraf generator. We also do electrophysiology
with electrodes embedded in mammalian brains; heaven help the poor
research bunny that gets 5k thru the cerebral cortex!
I've been thinking about the use of heel straps to mitigate the static
problems. My problem is this: it's unreasonable to cover the vast area
of our lab with antistatic floor mats. Will the heel straps work on any
old floor?
Also, a coworker gave me a bottle of something called "Staticide", which
has somewhat scant directions...anybody ever use it? Is it a "spray on"
static mat?
Mike H.
>Check it out, folks!
>www.esdjournal.com/techpapr/sfowler/wireless.htm
>A good review and dissection of wireless wrist strap technology...
>
>For those of you who don't want to look at the link, the page basically
>says
>that it comes with a normal wire, and all that is on the inside is a 1M
>resistor... IOW, it works as long as it's connected to its grounding wire.
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>Rats. And here I thought I'd found a good solution to my problem...
>
>I work in a research lab with lots of somewhat touchy equipment. It
>also happens to be in central Iowa, USA, which is about as arid as the
>Gobi desert this time of year, so as you can imagine, everyone is a real
>live walking talking Van DeGraf generator. We also do electrophysiology
>with electrodes embedded in mammalian brains; heaven help the poor
>research bunny that gets 5k thru the cerebral cortex!
That should end his plans for world domination, or at least confuse them a bit!
>I've been thinking about the use of heel straps to mitigate the static
>problems. My problem is this: it's unreasonable to cover the vast area
>of our lab with antistatic floor mats. Will the heel straps work on any
>old floor?
Only if it's somewhat conductive. Concrete is.
>Also, a coworker gave me a bottle of something called "Staticide", which
>has somewhat scant directions...anybody ever use it? Is it a "spray on"
>static mat?
Not very effective.
You don't necessarily need to be grounded so much as you need to be at the same potential as the lucky bunny. Conductive tabletops, and a rule to always touch the table top (where the rabbit foot donor is sitting) should do it.
Here, I have wood floors, and unfinished wood tabletops, and I normally work in cotton socks. So far, I haven't measured more than 600V and that's pretty unusual.
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>I've been thinking about the use of heel straps to mitigate the static
>problems. My problem is this: it's unreasonable to cover the vast area
>of our lab with antistatic floor mats. Will the heel straps work on any
>old floor?
For anti-static floors go looking for anti-static linoleum used for clean
rooms and (I think) operating theatres, both places where static is a
definite no-no. I know that I have had work bench tops finished with
anti-static linoleum before.
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Humidify your lab. If you can get the RH above 60% you will have far less
static problems. A large sized humidifier from Walmart can achieve this
at low cost, unless your lab is huge. Then also implement antistatic
procedures on the bench where you are working on your rabbit-steaks. A
cheap antistatic pad under the hapless rabbit and a touch-me-first metal
bench should do the trick nicely. The antistatic pad I have is pretty
cleanable, and plenty big to saw open a rabbit, although I have never
tried it out with blood stains.
>I've been thinking about the use of heel straps to mitigate the static
>problems. My problem is this: it's unreasonable to cover the vast area
>of our lab with antistatic floor mats. Will the heel straps work on any
>old floor?
For anti-static floors go looking for anti-static linoleum used for clean
rooms and (I think) operating theatres, both places where static is a
definite no-no. I know that I have had work bench tops finished with
anti-static linoleum before.
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> Here, I have wood floors, and unfinished wood tabletops, and I normally
work in cotton socks. So far, I haven't measured more than 600V and that's
pretty unusual.
600 volts is only about 20 times more than the gate of a typical FET will
stand (about 40 times for a typical logic FET). A PIC with protection diodes
would probably survive it OK except on pin RA4 (no upper diode) or
equivalent.
Russell McMahon
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> A cheap antistatic pad under the hapless rabbit and a touch-me-first metal
> bench should do the trick nicely.
Butyl rubber (sold for flooring and pond membranes) is a MUCH cheaper
surface than "proper" antistatic mats. Resistivity varies somewhat with
manufacturer and batch. Some rubbers are nicely conductive on one face and
not on the other.
Take a standard multitester. Set it to a high ohms range (20M preferably).
Press 2 probe tips into rubber at various points. If you get any reading at
all the surface will probably work. Some have VERY low readings (1 few k
ohm) and are not good to run circuits on without an insulator between. They
can also be a hazard when mains electricity is in use - but no more so than
any other earthed surface.
I use butyl rubber sheet on my work benches. Even cheaper are the wrappings
they put around the large bundles when shipped (here anyway). They are the
same material but treated as scrap. Here they sell them cheaply for funds
for the staff social club - very economic antistatic mat. Also good for 100%
waterproof doll house roofing (and no esd to boot).
Russell McMahon
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Salesgeek stand by their (useless) product.
Response to my email.
The article makes a one line comment and the link is then back to their ad
(as far as I could see).
Thanks for your recent e-mail. Actually, this strap works just fine just
the way it is shipped. This article briefly mentions the cordless grounding
strap:
"If you don't want to deal with a ground, $39 cordless wrist straps, based
on a technology that uses the Corona principle to dissipate static without
using a ground, are also available at Directron.com. Industry experts say
they're not as effective as a true grounded wrist strap, but they're better
than taking your chances."
> I've been thinking about the use of heel straps to mitigate the static
> problems. My problem is this: it's unreasonable to cover the vast area
> of our lab with antistatic floor mats. Will the heel straps work on any
> old floor?
>
> Also, a coworker gave me a bottle of something called "Staticide", which
> has somewhat scant directions...anybody ever use it? Is it a "spray on"
> static mat?
In your extreme and mobile environment you will need to use a genuine old
fashioned grounded earth strap. Sorry :-(. Heel grounders will improve
things but without tests of floor impedance to ground etc they can't be
guaranteed. Staticide gets eg carpet down to the "doesn't hurt when I walk
on it" level but can still allow eht at levels which will zap semiconductors
(and presumably bunny brains). Negative ion generators at work benches can
help stationary workers but are not practical over any distance. And
presumably can pump you up in the opposite direction.
Large floating metal plates capacitively coupled to ground and poorly
resistively coupled to ground (via high resistance leakage) CAN prevent
voltage rise from small discharges due to voltage being capacitively divided
(or think of it as charge sharing) allowing subsequent leakage to ground.
But you'll need earth straps if you are serious or a proper qualification of
your floor.
Russell McMahon
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Since we work with static sensitive devices daily, we all have grounding
straps, and we spent a hell of a lot of money on supposedly anti static
carpet, which is patently useless!
Liam O'Hagan wrote:
> Since we work with static sensitive devices daily, we all have
> grounding straps, and we spent a hell of a lot of money on supposedly
> anti static carpet, which is patently useless!
>
> Depends a lot on what shoes we wear too....
Cast iron leg shackles with heavy steel chains back to a central grounding
point should to the trick. It will also cut down on those silly coffee
breaks, lunches, time to go home and sleep, and all those other whiny
excuses the peasants come up with to avoid working.
*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com
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Olin Lathrop wrote:
> Cast iron leg shackles with heavy steel chains back to a central grounding
> point should to the trick. It will also cut down on those silly coffee
> breaks, lunches, time to go home and sleep, and all those other whiny
> excuses the peasants come up with to avoid working.
Hmm...this coming from the guy who is looking to hire. Did your former
employees finally waste away to just bones? :)
Josh
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Seriously though, we have full anti-static flooring installed (tiled, not
carpeted), ionizers on each bench, anti-static chairs with drag chains to
the floor, wrist straps, ESD shoes, ESD bunny suits and nitrile gloves
(which are static dissipative vs latex), and humidity control of the room.
It seems MEMS devices don't like ESD.
Dave
At 05:16 PM 12/18/2003 -0500, you wrote:
>Cast iron leg shackles with heavy steel chains back to a central grounding
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>
> Cast iron leg shackles with heavy steel chains back to a central grounding
> point should to the trick. It will also cut down on those silly coffee
> breaks, lunches, time to go home and sleep, and all those other whiny
> excuses the peasants come up with to avoid working.
I think you still need those items to enter Australia - so I guess they
don't have an ESD problem :-)
*************************************************
Cast iron leg shackles with heavy steel chains back to a central grounding
point should to the trick. It will also cut down on those silly coffee
breaks, lunches, time to go home and sleep, and all those other whiny
excuses the peasants come up with to avoid working.
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Why; --into bondage? Olin dressed in leather, whip, .... My what a nice
holiday image... :') Thank you sir! May I have another?
{Original Message removed}
But then all the metal is amalgamated (sp?) with the Hg and becomes the
consistency of silly putty!
Dave
At 04:41 PM 12/18/2003 -0700, you wrote:
>:-)
>3" of liquid mercury for the whole floor surface. Added benifit if you drop
>your hand tools/parts you can collect them with a net.
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On Thursday, Dec 18, 2003, at 15:41 US/Pacific, Dal Wheeler wrote:
> 3" of liquid mercury for the whole floor surface.
Mercury is SOOOO passe'... There's a gallium/indium/tin
alloy that's liquid down slightly below 0c that's much
more in keeping with modern electronics technology...
At 08:59 AM 12/19/2003 +1300, Russell McMahon wrote:
>> Here, I have wood floors, and unfinished wood tabletops, and I normally
>work in cotton socks. So far, I haven't measured more than 600V and that's
>pretty unusual.
>
>600 volts is only about 20 times more than the gate of a typical FET will
>stand (about 40 times for a typical logic FET). A PIC with protection diodes
>would probably survive it OK except on pin RA4 (no upper diode) or
>equivalent.
Most devices are ok with it. I wouldn't handle bare laser diodes without additional protection, and that is my peak measurement so far.
> >> Here, I have wood floors, and unfinished wood tabletops, and I normally
> >work in cotton socks. So far, I haven't measured more than 600V and
that's
> >pretty unusual.
Wood is good!
> >600 volts is only about 20 times more than the gate of a typical FET will
> >stand (about 40 times for a typical logic FET). A PIC with protection
diodes
> >would probably survive it OK except on pin RA4 (no upper diode) or
> >equivalent.
> Most devices are ok with it. I wouldn't handle bare laser diodes without
additional protection, and that is my peak measurement so far.
Most, yes. Some, definitely not. An unprotected FET gate can be about as
bad as they come (tens of volts breakdown).. A Gunn diode is pretty
sensitive too I believe - not that many people will encounter a Gunn diode
from one years end to the next. Most modern ICs are pretty safe at that
voltage with the normal levels of esd source capacitance represented by a
human body. Store the charge from several people to a large enough capacitor
and it may be different. A filing cabinet may qualify. Murphy says that such
unlikely things can happen if its important enough that they don't.
In a previous corporate life time and long long ago (in a universe far ... )
we used to be able to increase shock capacity by having a group of people
hold hands and shuffle across carpet together. Shuffle shuffle shuffle zap
... ! Everyone in the string as well as any target received much the same
level of shock.
> As opposed to the long velcro gloves needed when entering NZ! ;)
>
At lest the Kangaroos are safe in Australia - bit hard to catch one wearing
ball & chain :-)
*************************************************
Right, well, thanks then everyone! I think heel straps and a small mat
under the experiment table are the way to go...that way, anyone getting
near the hapless lagomorph will have to discharge themselves.
Also probably one or two really large humidifiers.
It continually amazes me the level to which things around here are not
engineered. As I understand it, I may be the only full-fledged engineer
on staff in any major research lab of this type. It's quite bizarre some of
the things that have been just overlooked in the past which could have
major consequences for the data being collected.
It has made me question the validity of scientific findings of all sorts.
> > I've been thinking about the use of heel straps to mitigate the static
> > problems. My problem is this: it's unreasonable to cover the vast area
> > of our lab with antistatic floor mats. Will the heel straps work on any
> > old floor?
> >
> > Also, a coworker gave me a bottle of something called "Staticide", which
> > has somewhat scant directions...anybody ever use it? Is it a "spray on"
> > static mat?
>
>In your extreme and mobile environment you will need to use a genuine old
>fashioned grounded earth strap. Sorry :-(. Heel grounders will improve
>things but without tests of floor impedance to ground etc they can't be
>guaranteed. Staticide gets eg carpet down to the "doesn't hurt when I walk
>on it" level but can still allow eht at levels which will zap
>semiconductors
>(and presumably bunny brains). Negative ion generators at work benches can
>help stationary workers but are not practical over any distance. And
>presumably can pump you up in the opposite direction.
>
>Large floating metal plates capacitively coupled to ground and poorly
>resistively coupled to ground (via high resistance leakage) CAN prevent
>voltage rise from small discharges due to voltage being capacitively
>divided
>(or think of it as charge sharing) allowing subsequent leakage to ground.
>
>But you'll need earth straps if you are serious or a proper qualification
>of
>your floor.
>
>
>
> Russell McMahon
>
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> It has made me question the validity of scientific findings
> of all sorts.
Contrary to popular belief science is not into finding truths, at least
not directly. All it does is taling an awful lot of ideas an (slowly)
filter out the ones that are can be proven wrong. If you think the
'surviving' ideas of today are necessarily truths think of the surving
ideas anno 1900, or even 1800.
normally, one won't need any net. Iron, even lead and other metals will
swim on the surface of mercury. Only gold will sink. On the other hand,
mercury would solve kind of metals.
Regards,
Imre
On Thu, 18 Dec 2003, Dal Wheeler wrote:
> :-)
> 3" of liquid mercury for the whole floor surface. Added benifit if you drop
> your hand tools/parts you can collect them with a net.
>
>
> {Original Message removed}
The staticide is available in various forms. It is to be sprayed on
floors, mats, carpets and so on once a week or so. I have discoevred (by
making an educated guess and thentesting) that fabric softener has the
same effect. It is refreshed by spraying just plain water. Some floor
waxes also have this effect. Waxes are normally among the best insulators
available but apparently some of them aren't.
If you are worried about static get a static probe and wear it. It will
warn you from approaching anything with a potential != yours. You can make
one easily using a mosfet (2N7000 works), a battery, a led and a resistor,
but better rely on a professionally made one.
> Most devices are ok with it. I wouldn't handle bare laser diodes without
Apropos, what's the status of blue LEDs wrt static ? LEDs are not normally
considered static sensitive (or so they say in retail trade), but I think
blue ones are. No ?
>Also probably one or two really large humidifiers.
You probably just need a couple of large pot plants in the corners of the
room to keep the humidity at an appropriate level. Have heard of this being
done in computer rooms when the air conditioning dropped the humidity down
real low to a point where static was a problem.
>-----Original Message-----
>From: Alan B. Pearce [RemoveMEA.B.PearceTakeThisOuTRL.AC.UK]
>Sent: Monday, December 22, 2003 6:51 AM
>To: PICLISTEraseME.....MITVMA.MIT.EDU
>Subject: Re: [EE:] Grounding strap alternatives
>
>
>>Also probably one or two really large humidifiers.
>
>You probably just need a couple of large pot plants in the corners of the
>room to keep the humidity at an appropriate level. Have heard of this being
>done in computer rooms when the air conditioning dropped the humidity down
>real low to a point where static was a problem.
>
Yes, I have been known to keep a few large pot plants in the computer room
when I was much younger. It's true that they can reduce many kinds of static.
It can cause trouble if any narcotics officers stop by though. 8^)
> >Also probably one or two really large humidifiers.
>
>You probably just need a couple of large pot plants in the corners of the
>room to keep the humidity at an appropriate level. Have heard of this being
>done in computer rooms when the air conditioning dropped the humidity down
>real low to a point where static was a problem.
My wife has about 10 potted plants in our house (small ones, though) and we
have a 54 gallon (200+ liter) fish tank, and that just barely keeps our
house
humid. I still get the occasional shock.
It gets REALLY dry around here. Plus, I don't know what kind of potted
plant
to get in a room that has NO source of sunlight.
Mike H.
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----- Original Message -----
From: "Mike Hord"
> My wife has about 10 potted plants in our house (small ones, though) and we
> have a 54 gallon (200+ liter) fish tank, and that just barely keeps our
> house
> humid. I still get the occasional shock.
>
> It gets REALLY dry around here. Plus, I don't know what kind of potted
> plant
> to get in a room that has NO source of sunlight.
Mushrooms?
I've got a "grow light" in my office in the basement for my ficus. I probably
need more plants; as I haven't been able to keep the static down very easily in
the winter. I don't think there's much you can do with certain types of carpet.
RL.AC.UK>
