but for some reason it doesn't seem to be conductive at all. I've tried building a simple flex sensor with it using adhesive copper foil for the conductors and it doesn't work. So then, just to make sure it wasnt the copper foil that was causing the problem I tried touching the two terminals of my multimeter directly to the velostat with the multimeter set to 'resistance: 20ohms' at first and then to the diode (no resistance) setting and it's not actually conducting anything at all. Does thi sound odd to anyone? Am I doing something wrong? Surely it should be reading something.
Most copper tape has nonconductive adhesive on it.
As pwillard points out, it has a pretty high resistance. Meter leads won't cut it, you need larger contact area.
The standard way to measure is by something called "per square". Take two pieces of metal that are about 1cm square and place them 1cm apart. Now use your meter to measure the resistance with some pressure applied.
This works the same if you use just about any size as long as they are spaced apart the same as their size. So 10cm squares placed 10cm apart will give the same measurement.
Did you look at any of the links they gave in the auction? Note that they also point out that it is not conductive from one side of the sheet to the other, so the Instructables one won't work.
Hi again,
Thanks for the replies. If the velostat does not conduct from one side/ surface to the other then how is it working in this video? Stickytape Bend Sensor in less than 4 minutes - YouTube
Also, it's not the adhesive side of the copper strips which i have in contact with the velostat. and I have tried it at all resistance ratings on my multimeter
I suggest you ask the supplier to refund your payment. As the material is not conductive from one side to another it cannot have the stated volume resistivity.
It looks like your supplier has had previous complaints about the product description because their ebay listing includes these words in red: "Please contact us for any technical issues, or any other questions before opening a case or request, our team of engineers will answer your queries within 24hr."
I was quoting and commenting on an explicit reference to volume resistivity, your response was
a non-sequitor.
I think the actual volume resisitivity figure was meant to be in ohm-cm^2, not ohm/cm^2, ie
it was the resistivity normal to the plane of the sheet, not parallel, independent of thickness.
you place two metal sheets either side in full contact with the sample sheet, ie 1cm2 each.
you measure the resistance between the metal sheets, and get 4000 to 1000 Ohm depending on the pressure you exert on the sheet.
if I repeat 1) with 2cm2 sample and 2cm2 conductive sheets.
You have the equivalent of two 4000ohm resistors in parallel, so you should be able to measure 2000Ohms to 500Ohms depending on pressure.
Always making sure you pickup contacts are the same area as the sheet.
So the larger area of conductive sheet you use the lower the effective resistance, as long as you use the same area terminating sheet of copper etc,
The smaller the terminating sheet the larger the resistance you will have, so using a DMM prod on a sheet will not necessarily give you the figures you expect.
Tom...
That's in theory, must get some of this stuff and try it out.
Yes, and my first reply was not a confirmation that I thought it was a faulty product. It's more likely the behavior of what was sold is being misunderstood.
The units for what you are describing should not be Ω/cm2 because that would imply that if you double the area you would double the resistance. The units should be Ωcm2 or you could use S/cm2.
TomGeorge:
if I repeat 1) with 2cm2 sample and 2cm2 conductive sheets.
You have the equivalent of two 4000ohm resistors in parallel, so you should be able to measure 2000Ohms to 500Ohms depending on pressure.
I think you mean 500 to 2000 ohms.
TomGeorge:
That's in theory, must get some of this stuff and try it out.
Don't get the stuff from that Aura Communications. Their ebay listing states that the material is not conductive from one side to the other.
MarkT:
Anyway area resistivity is measured in ohms, pure and simple, none of this per-square nonsense.
No it is not, it is measured in ohms per square.
Did my final degree project back in the 70s on the Van der Pauw four probe method of measuring sheet resistivity in etched semiconductors.
Going to try a different supplier.
