What mechanism is in place to cause the following? - Page 1
Forum section: electronics / general

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 18, 2013, 03:25:46 am
content: Ok, I have a very odd situation that I'm trying to figure out.The scenario:4 wire Kelvin clips measuring a 100k resistor connected to my 3457ASitting on a 1ft x 1ft white ceramic tile.Under that is 1 inch thick what I assume is oak wood (Desk).About 29 1/2 inches down from that is a ceramic tile floor.Under that is concrete (It's in a basement).Now for the weird part.Stable reading on the meter..last digit flickers a little.I'm sitting in a typical office chair with cloth cover, plastic coasters and a high back.I'm wearing leather sandals.I'm not touching the desk or anything but the chair and floor.Ok..the really weird part....If I move my foot off the floor...even slowly...the resistance drops about 100 ohms or so.Without the sandals...it does nothing.If I move the test setup off of the ceramic tile to the wood surface, it also doesn't do it.I can repeat the process over and over again without fail. Faster movements appear to produce more drop.Any thoughts on what mechanism is in place here ? I'm thinking Piezoelectric effect somehow producing a voltage which is being picked up by the sense wires ?I just switched it to volts, it has a 10G ohm input impedance. The moving foot sometimes produces up to about 0.4V on the meter even with the 100k resistor still connected. I think I need to ditch the ceramic tile or get a grounded one.Jeff

author: UPI
author_rank: Regular Contributor
timestamp: January 18, 2013, 03:34:26 am
content: What happens when you put down the bottle?

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 18, 2013, 03:55:31 am
content: Quote from: UPI on January 18, 2013, 03:34:26 amNot exactly a scientific analysis. Something along the lines of...perhaps it's electrostatics at work might have been a little more constructive. But hey, I get it.

author: UPI
author_rank: Regular Contributor
timestamp: January 18, 2013, 04:06:16 am
content: OK. No more funny stuff.Try a ground strap on your wrist to see if the problem is greatly reduced.Do you have fluorescent lighting above? Turn off the lights.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 18, 2013, 04:16:32 am
content: I do have overhead fluorescent in two fashions. One of those dual bulb magnifiers and a quad 4 ft tube assembly with those obnoxious daylight tubes on the ceiling.Well your on to something, an earth grounded wrist strap stops it from happening. Perhaps I should ground the wood desk...Jeff

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 18, 2013, 04:31:25 am
content: I failed to report that turning off the lighting doesn't help. The ground strap reduces it by about 10 orders of magnitude. I'm just curious how many other items might be impacted by whatever this issue is. It might just be static...but is it is it's a very odd delivery method.Thanks,Jeff

author: UPI
author_rank: Regular Contributor
timestamp: January 18, 2013, 04:36:10 am
content: It is most likely the chair fabric causing a large buildup of static.http://in.mouser.com/ProductDetail/Techspray/1726-QT/?qs=sGAEpiMZZMtYFXwiBRPs018OUN3csyU5

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 18, 2013, 04:41:08 am
content: I guess it's just me...or the shoes. I took the chair out of the picture and even standing up it still does it. I guess this is a reason to get the correct types of matting, etc for your bench. I hate having to wear a wrist strap all the time. But I guess if that's all that will solve it then that's what I'll have to do. It doesn't completely solve the problem, but it at least cuts it way down.Jeff

author: UPI
author_rank: Regular Contributor
timestamp: January 18, 2013, 04:50:39 am
content: I know what you mean. I tried wrist and foot straps in the shop but the guys either wouldn't wear them or they would wear them home and forget to bring them back.Now, I just use anti static spray on the vinyl covered chairs, put ground drag chains on the chair bases, ESD mats on the grounded formica/metal benches and I bark at everyone when they don't ground themselves to metal or the ESD mats after walking across the room.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 18, 2013, 05:02:58 am
content: What's also funny about all of this is how I often wondered why the 3457A would jump around from time to time. Just tonight I put my movements in direct correlation to the jumps.As a for fun test I stepped back about 6 ft. It's still very much detectable from that distance. The ceramic tile floor must be playing in to all of this. Without the shoes it's all good (but cold). Perhaps just some carbon based footwear or something. I like the drag chain idea on the chairs, that might help. Anything to keep from building up a charge. I'm just blown away by the distance this can travel. One has to wonder just how much EMI the human body produces. I also figured out that the longer I stay still the more impact is produced. Fascinating and annoying all at the same time.Jeff

author: SeanB
author_rank: Super Contributor
timestamp: January 18, 2013, 04:13:20 pm
content: You could, or at least place a grounded metal mesh under the desk covered again for protection ( yours not anything else) with a thin plywood or masonite sheet. Will discharge the wood and provide a shield.As a good way to reduce static wash the floor with a mop, but do not use soap rather fabric softener. That will dissipate static charge quite well. Just a cupful in the bucket of hot water and mop it, then leave to dry. Do the chair feet and the base as well with this on a cloth to clean it and leave a thin film as well. Reduces static a lot.

author: (In)Sanity
author_rank: Regular Contributor
timestamp: January 18, 2013, 04:19:56 pm
content: Thanks Sean, I know the fabric softener trick as a spray, but never thought about using it to wash the floor. Great idea.

author: SeanB
author_rank: Super Contributor
timestamp: January 18, 2013, 06:40:57 pm
content: I got that one from the guys who do professional floor cleaning and wet extraction. When they do an office complex they put a capful in the water as the final rinse. it leaves the floor static free and the whole office smelling fresh. Also covers any musty smells if there has been water spilled on the floor which was the reason they were called out.I had them in as when I went to work one evening late I turned in and water was splashing down the back stairs. Opened up, turned off the tap that had been left on ( water had been shut by metro to repair a burst in the street) and then went around and turned on all the lights ( heat load) turned on all the fans ( move air) and turned all the aircons on to ultra fridge mode ( get the air super dry) then locked up and went home and left it like that till the Monday. Got rid of most of the 2cm puddle, though a few chipboard cupboards and desks did not survive. took them and used circular saw on the bottoms and made new ends for some.