EEVblog 1489 - Mystery Teardown

[EEVblog]

Teardown of a bizarre looking Banshee 343 Ultrasonic Gas Leak Detector

Thumbs up this video and pinned comment if you want to see a countdown timer refit project!

Datasheet: https://www.instrumart.com/assets/Net-Safety-Banshee343-datasheet.pdf
Manual:  https://www.instrumart.com/assets/Net-Safety-Banshee343-manual.pdf

[ace1903]

Can we expect detailed photos on www.flickr.com/photos/eevblog/ site?
Want to try to identify that mysterious ADC chip.
 

[golden_labels]

Soldered-in fuse in that kind of equipment seems fine to me. I assume that, due to safety requirements, the PCBs are not serviceable.

[Kleinstein]

Soldered fuses are not that rare - just using classic 20 mm fuse to be soldered MELF like is a bit odd.  Not all fuses (depends on the speed and current) like the soldering and may be damaged, especially with lead free soldering.

[Barny]

The custom optocoppler where in EEVblog #1277 - Electric Fence Controller Teardown
@05:20

And: EEVblog #1292 - $2 Meter vs JVA Electric Fence Controller! @11:00


An individual count down thingy in the lab would be funny.
But why don't go the full way & use C-cell battery-sticks wrapped in red paper, alarm - beeper for tamper / opening alarm ....

On the other hand:
You could make an nice alarm-clock out of it using one of the nice RTC chips.

[Barny]

Could it be that the rods in the video are only to protect the sensors from impact?
Have the rods small holes drilled in them?
(In the 0,1 to 1mm region)
If thats the case, perhaps the whole thing gets pressurised externally with air or nitrogen with an external pressure line and produce the "real test leak" that way.
This would be the cleaning function too.

Are the wires to the potted part under the shiny dome NTC or PTC resistors?
Perhaps the heater get mounted externally if needed & the wires are only to monitor the heater.

Soldered-in fuse in that kind of equipment seems fine to me. I assume that, due to safety requirements, the PCBs are not serviceable.

I think its due to cost reduction, prevent corrosion on the terminals & prevent the fuse from falling out when the thing gets dropped.

[tunk]

In addition to a countdown timer, maybe you could add a big vibration motor and a speaker?

[tszaboo]

You can see lasered EX marking on those ports, they were ordering special explosion-proof bolts for this.
Those sensors can be outside the EX d area, and have thinner metal wall, because there will be limiters in between. They have less power and current and everything so they cannot set the gas on fire. This is the marking "ib" on the type plate, and this is why we have optocouplers and large resistors on that second board.

I would correct a few things that you said at the end. This is not really "intrinsic safety", only for the sensors. This is "protection by flameproof enclosure". Meaning that it's not gas-proof, the flammable gas can totally get into the enclosure, and it can explode in case of a failure. The flameproof enclosure can handle this small explosion inside and the protection makes sure that the entire gas plant is not set on fire.
That being said I'm not in the design of EX d stuff.
Thanks for the teardown.

[bsdphk]

Could it be that the rods in the video are only to protect the sensors from impact?

The studs are so you dont destroy the connector.

On one of the early sequences, you can see that the "cup" containing the sensor has matching grooves for the stud, so that you can only get it to fit in the right orientation for the connector.

It may even look like the connector is a bajonet style, as the groove in the "cup" is not just a hole but a grove.

[Kleinstein]

The outer case looks like it has provisions for some air blowing just a cross the sensor from the side. So it really looks like there is the option to have studs with air, but the currently installed ones don't look like they are made for it. Just of the orientation of the connectors smaller pins would be used. The studs have quites some play and would be only a crude first alignment.

[thm_w]

Could it be that the rods in the video are only to protect the sensors from impact?
Have the rods small holes drilled in them?
(In the 0,1 to 1mm region)
If thats the case, perhaps the whole thing gets pressurised externally with air or nitrogen with an external pressure line and produce the "real test leak" that way.
This would be the cleaning function too.

Are the wires to the potted part under the shiny dome NTC or PTC resistors?
Perhaps the heater get mounted externally if needed & the wires are only to monitor the heater.

Soldered-in fuse in that kind of equipment seems fine to me. I assume that, due to safety requirements, the PCBs are not serviceable.

I think its due to cost reduction, prevent corrosion on the terminals & prevent the fuse from falling out when the thing gets dropped.

The youtube replies from Mike/Sean/others are relevant:

Mike:
The principle of this type of protection is that they assume the thing will fill with gas and ignite, and the enclosure must not allow any flame to escape. (During the approvals process, they test this using either hydrogen or acetylene + oxygen, with expensive gas analysers to get an accurate mix to meet the standards)
This is why it has a long, tight-fitting flange on the main enclosure joint. The terminal area has less stringent requirements, so no flange, but also no active components. 
I think the external glands ( called line bushings) specced for use with these are designed to be gas-tight and not allow gas to go through the cable, hence the lack of per-core sealing here - they typically have a bulkhead filled with epoxy, with the wire stripped bare where it passes through the resin.

This is not the same thing as intrinsic safety - with IS, the protection is provided by limiting voltages and currents by design, whearas explosion proof (Ex-D and Ex-E from my hazy memory) is used where this is not practical due to power requirements.

The soldered fuse is not uncommon - a major part of design for Ex approvals is not so much designing it to be safe, but designing it to be easy to prove it's safe. It is standard practice to include fuses, zeners etc. that have no chance of ever acting in normal or even fault conditions, just to make it easy to compartmentalise parts of the circuit to make it easier to evaluate for approvals.

Including a fuse is a simple & cheap way to prove that the current can never exceed a certain amount under any circumstance - the standards define how much current can pass a fuse of a particular rating, the number 1.7x rings a vague bell. It also reduces the risk that some idiot replaces the fuse with the wrong value ( "less danger of it blowing guv....").

Sean:
 Probes into the sensor heads are there to have the heater blocks screwed in instead of the blank probe, to heat the actual sensor itself in use in icing conditions. Self cleaning probably uses those probes, and then a separate port into the case that provides the air pressure for cleaning, via stainless steel pipes and a spiral tube that connects the ports to the top. That is why there are 2 recesses in the probe, one for the cleaner, not fitted and drilled to spec, or the heater, fitted to all but in temperate use only the dummy heater block.

Mike Fochtman
Worked on 'explosion proof' fans and such in the Navy.  They aren't completely 'gas tight', but the idea is that any explosion inside won't ignite the atmosphere around them.  So for example, submarine battery fans (H2 hazard) had to have very close tolerance fits.  H2 might actually get inside, but if it ignites the flame can't 'blow out' through any of the tiny cracks/ crevices.  Sort of like how a steel screen placed over a bunsen burner, the flame won't go up through even though hot gases flow up through the screen.

And of course the casing is strong enough to not rupture if the inside is filled with the 'perfect' mixture of explosive gas/air.

So that interface cable might let gas seep along it between all the individual conductors, but that's fine.

[golden_labels]

All people coming with the bomb-like ideas: that reminds me of Mark Robber’s glitterbombs. For many reasons I do not suggest that to Dave and strongly discourage any of you from doing such things, but just imagine a thief stealing a box with something like that, opening it and seeing the countdown timer.

[Neutrion]

So many of you are suggesting that the case would withstand an explosion by a full filling of perfect air/gas mixture? It is so hard to belive.

As for the countdown timer:
I would include the text as well: "Fuse nr 1-2-3 OK" and fill the thing  with lead of course.

And how to get it through the airport sec.? Its easy: "This is a design kitchen timer given to me by that nice guy with a big beard at the entrance as a present."

Most important is, to have 1-2 hidden camera guys focusing on the faces of the security guards while saying this, and also to have someone to upload the video later.  We don't want to wait for months to watch it.

It might could be also hacked to a swiming pool speaker emitting dolphin conversations. Or as a star/galaxy projector. It's so cool, it begs to be repurposed somehow.

[tszaboo]

So many of you are suggesting that the case would withstand an explosion by a full filling of perfect air/gas mixture? It is so hard to belive.

It's been certified to that, otherwise it wouldn't be on the market. And this sort of certification is only given if they are done by a third party, a NoBo, with actual tests performed in the worst case conditions multiple times.

A flameproof equipment offers an enclosure in which the parts which can ignite an explosive gas atmosphere can be placed. It withstands the pressure developed during an internal explosion of an explosive mixture, and prevents the transmission of the explosion to the explosive gas atmosphere surrounding the enclosure.
A flameproof enclosure must meet three criteria:
• Contain an internal explosion without permanent distortions.
• Guarantee that the explosion cannot be transmitted to the surrounding atmosphere.
• Have a temperature at any points on the surface that is lower than the self ignition temperature of the surrounding gases or vapors.

[Neutrion]

Hi!
It was not a serious doubt from my side, but the feeling, that I had, that it had to be a bit more thick for that.
Dave could also fill it, and explode it in the lab as a nice experiment. (Or at an airport of course.)