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I am working for a safety company and we need to certify how we can use some nitrile gloves with touch screen, I read that your finger needs to be at .5mm to the touch screen to make it work. So depending on the thickness of the glove this could work or not. Any expert on this?

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  • \$\begingroup\$ In practice, the distance a touchscreen will tolerate varies - some can at times fail to register direct skin contact. Most seem to work a lot better when one hand is behind the device, than if it is sitting on a non-conductive surface and being poked by a finger attached to an otherwise distant body. \$\endgroup\$ – Chris Stratton Aug 6 '14 at 16:09
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Even heavy duty nitrile gloves are a handful of mils thick (e.g., here), so you're unlikely to reach 20 mil for most gloves (roughly 0.5 mm). Some do seem to peak out at 14mil, though, so you need to be a bit careful. This paper talks about designing for glove use. Techniques involve careful tuning of the capacitive field by tweaking the distance between touch screen plates, increasing the power output of the driving electrode, and minimizing cover plate thickness.

As to how to certify, that's probably tougher. Microsoft offers a standard at this site that you might find a suitable starting point. You might find it easier just to develop a suitable specification that satisfies your customers, developing a test, and meeting it. Another option to consider would be working with a touch screen vendor to see what their standards are and whether they have a product that verifiably suits your use.

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I don't claim to be an expert on capacitive touch screens, however note that Nitrile rubber has a dielectric constant of about 2.5, which effectively reduces the thickness of the rubber by that ratio compared to air.

Typical thicknesses of Nitrile gloves are 0.004" and 0.0063" (0.1~0.16mm) so even the thickest ones are only equivalent to about 10% of what you say is the allowable gap in air.

Things like cotton gloves would be considerably more problematic.

See, for example this parallel plate capacitor calculator.

The way the device is held may affect the functioning of the touch screen, especially if an external power supply is attached.

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  • \$\begingroup\$ When comparing dielectrics, you need to compare against the dielectric constant of the COVER of the touch screen, not against free air, as without gloves, the fingers would be touching the cover. Glass is about 3.8, so you're actually a bit worse off, as your distance to the electrode is increased, and your effective dielectric is lowered. \$\endgroup\$ – Scott Seidman Aug 6 '14 at 15:50
  • \$\begingroup\$ @ScottSeidman The claim I see in the question is that a 0.5mm gap in air is sufficient for the keypad to operate. I'm not questioning that claim, just saying that 0.5mm in air is equivalent to 1.25mm in Nitrile or 0.15mm in Nitrile + 0.44mm in air. \$\endgroup\$ – Spehro Pefhany Aug 6 '14 at 15:54
  • \$\begingroup\$ Ahh, got it. Comparing against the air gap should be fine \$\endgroup\$ – Scott Seidman Aug 6 '14 at 15:58
  • \$\begingroup\$ @ScottSeidman am not an expert in this terminology, when you say that Nitrile is equivalent to 1.25mm because Nitrile has a dielectric constant of about 2.5. Does this mean that Nitrile is a good conductor or electricity so you could use a gloves of 1.25mm? Sorry, I am asking stupid questions, I just want to clarify. Thanks \$\endgroup\$ – MarinJL Aug 6 '14 at 20:10
  • \$\begingroup\$ It means that the layer of Nitrile is indistinguishable from a much thinner (1/2.5) layer of air as far as capacitance is concerned (making some reasonable assumptions about geometry). Dielectric constant is also known as relative permittivity (relative to vacuum, and air is almost the same as a vacuum in this respect): en.wikipedia.org/wiki/Relative_permittivity \$\endgroup\$ – Spehro Pefhany Aug 6 '14 at 20:24
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It depends on the touch screen technology, and on the touch sensor.

About the technology: I guess you are speaking about capacitive touch screen, but in your question you did not specify it.

About the touch sensor, I say it depends because I've worked in a company developing the sensor chip making the multi touch detection, tracking, and reporting to the OS. It clearly depends on the screen itself, physical properties like mutual capacitance of the diamonds, and on the drive signals, and the overall SNR. Plus it also depends on the performance of the image processing engine. Some vendors would propose a hovering feature, since they could achieve a more sensitive sensor.

The touch detection specifications are given by Microsoft for MS certification process. I guess it's the same for other OS providers.

For your case, I suggest you make the gloves behave like a finger, from the electrical point of view, at the contact of the touch screen. Forget the thickness of the gloves, and add a conductive material on the finger tip, that makes it success for all touch screens on the market.

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