Safety of PCAP touch display in highly flamable gases environment - Page 1
Forum section: electronics / projects

author: ricko_uk
author_rank: Super Contributor
timestamp: May 27, 2022, 06:33:59 am
content: Hi,A system I am designing can sometimes (rarely) be used in environment where extremely flamable and very easily ignited gases can be present in the air. To the point that in those environments all personell has to be regularly grounded to avoid static charge build-up.So I initially specified a resistive touch panel for the display because I thought the projective capacitive one might induce/create charges in the operator and even if minute, they might then somehow discharge through the equipment and/or through the person somewhere else in the lab.But now the customer is asking for multi-touch capacibilities (not in the initial specs) so I am wondering whether my original thinking was correct and we better stick to resistive? Or whether PCAP is perfectly safe?Thank you

author: jbb
author_rank: Super Contributor
timestamp: May 27, 2022, 07:33:52 am
content: Errr, no idea? Maybe contact your safety certification lab?Multi-touch might turn out to be a ‘desirement’ rather than a requirement :-)

author: CaptDon
author_rank: Super Contributor
timestamp: May 28, 2022, 12:57:53 pm
content: SpaceLabs equipment was designed for and used in flammable and explosive environments. Their touch screen consisted of infrared emitters on the top and left side of the screen area and infrared sensors on the right and bottom of the screen area. This worked extremely well and safely. You only had to break the beams with your finger or any object for that matter and didn't even have to make physical contact with the screen. It was amazing to even imagine any device with a C.R.T. was allowed into those environments due to arcing and static buildup and typical flaming components during failure mode!!

author: voltsandjolts
author_rank: Unknown
timestamp: May 28, 2022, 01:30:56 pm
content: Quote from: ricko_uk on May 27, 2022, 06:33:59 amSo, erm, your product is ATEX certified...right?Thepro'sseem to have resistive and cap sense options.

author: ricko_uk
author_rank: Super Contributor
timestamp: May 30, 2022, 11:24:07 am
content: Thank you all!The client is looking into the certifications needed so I don't yet know. But from voltsandjolts link it looks like PCAP might be ok.If anybody else has experience or they know whether the amount of capacitance used in PCAP might cause electrostatic buildup and;or a spark please do let me know. Any feedback/info is always welcome!Thank you

author: tszaboo
author_rank: Super Contributor
timestamp: May 30, 2022, 11:58:19 am
content: Your product needs to be ATEX certified to be able to use it in an environment like that.The client needs to be fully informed on what they can and cannot install, its their Ex responsible person who need to define the zoning and gas group. You should absolutely refuse to do anything before that happens, because projects need total redesign for a single character change in those zones and gas groups.After that's done, you should be aware what you need to do to certify a product to the relevant standard. If you never did any project like that, get a consultant who did, it can save you months of work, if you don't approach the project correctly.

author: Terry Bites
author_rank: Super Contributor
timestamp: May 30, 2022, 02:49:51 pm
content: Buy a certified item an sue them when it all goes horribly wrong. Do you want it onyourconscience?

author: razvan784
author_rank: Regular Contributor
timestamp: May 30, 2022, 03:36:35 pm
content: Quote from: ricko_uk on May 30, 2022, 11:24:07 amRespectfully, I think you are missing the point by a wide margin. Your problem is not about static charges, it's about operating electrical equipment in potentially explosive atmospheres.I don't see how a capacitive touchscreen can induce static charges on an operator. Does your capacitive-touchscreen-enabled smartphone ever do that?One aspect of ATEX is indeed that no dangerous condition is generated during normal operation, but it is also important that no such condition occurs because of faults and failures. That is why ATEX-certified devices employ various measures, such as limiting the available energy (intrinsic safety), or enclosing the device in a flameproof enclosure - these protect against explosion even in case of electrical failures (shorts, insulation deterioration, random component failure etc).As with anything safety-related, I recommend you read up on relevant legislation and standards, as my colleagues have already suggested, instead of taking random advice from the Internet.

author: ricko_uk
author_rank: Super Contributor
timestamp: May 30, 2022, 09:48:53 pm
content: Thank you all for the info/feedback!