EEVblog #603 - Gas Sensor Teardown - Dräger Multiwarn II

hi welcome to teardown Tuesday this is an old mailbag item that we got it's a dragger multi worn and it it was sent in by andreas and he's from Germany so thank you very much Andrea sorry it took so long to get around to it what it is is a warning system that's designed to detect different types of gasses you might be able to see different sensors in there and this particular unit can actually accept different plug-in modules for this up to i think there's 35 different sensors for 35 different types of gas or something like that with dozens of different plugins that you can plug into here and it's a gas detection system there's an alarm on the top and it flushes a light and sounds a big siren out siren you know screaming if it detects um you know a combustible gas or something like that or a lack of oxygen even for example and they're used by emergency service for services for example Fire Brigades might have these are used in the mining industry any sort of underground sort of you know confined spaces type thing to warn you you just carry it around with you it's battery-powered carry it around with you and it detects all these nasty gases which could kill you or could explode or something like that so you really have to be careful so this could be relatively interesting inside although I think all of the interesting stuff is really inside the actual sensors themselves and how they work so yeah I don't think we're going to get too much into that side of things but anyway um it is an intrinsically safe product as the intrinsically safe the EXR symbol there and what that means is this is designed and certified to go in underground situations like mines where there are these explosive gases and things like that and well it's not designed to ignite though so it doesn't matter how this thing is used where you turn off and on or you or it goes off you know the siren goes off or you plug the battery in or something like that or it fails internally it's designed to be intrinsically safe so it doesn't ignite any of those gases and there's a lot of certification which goes into intrinsically safe products like this so yet let's check it out it's got a dot matrix our LCD this one is faulty I believe andreas said it was faulty it was too expensive to repair so they just scrapped it it's got a NiCad battery pack in the back here which we can take off a there we go and d25 connector inside that's really rather interesting so this is the NiCad battery pack that presumably got some circuitry in here charging circuitry and other such stuff like that but there you go that just plugs in and we can got some screws on the back let's open this puppy up and see so the first thing we'll do is just take off this module it is designed to come out so you can plug they're designed to be user replaceable so like for example if a if the fire brigade was on you know on headed to a fire you know in a in a chemical factory or something like that they may decide on you know they know ahead of time what factor it is and what sensors to put in here they could just replace this module in here and it looks like we've got a rubber surround so they could they could replace that on route there's a little port there obviously that's for outside air I'm presuming that this has maybe well it's got five ports I'm not sure you know that's a free air port there but also there was a port on the side here so I'm not sure if that's like the fresh air sensor or something like that permanently built into the thing because this is designed to be calibrated in fresh air so you can turn it on apparently and then run the calibration when you're out you know in the clean fresh air and then that just that just calibrate it recalibrates the thing for the current ambient environment that you're actually in generally fresh air but it looks like that doesn't come out it looks like you so much for user user replaceable it looks like we have to yeah it's user oh okay it's bit compliant that so it is user replaceable but for so much for the so much for the firemen changing the thing in the in the back of the truck on route to a fire oh well so will that pop out there we go so aha there we go and these are design to be are plug and play modules so IE they've got little identifiers in them so that the firmware inside knows which one you've plugged in so you don't have to reconfigure it or anything like that in software you just plug it in it's got an automatic ID system it knows what it is and it recalibrates itself now here we go there must be some sort of pump system in here because this looks like as we said came through that filter there's that extra intake over there and possibly that's linked to the outside here so that may be that's probably the pump so where they're actually pumping that around and for what purpose I'm not entirely sure but like how do you get these things out they're supposed to be user replaceable I guess you have to get a pair of pliers on there and pull them out mm-hmm should be that whole assembly in there as we saw before is sort of its own rubber shock mount and I guess it's got to do that to reduce the noise and possibly vibration from the pump I'm not sure if the pump continuously operates when you switch this song on I wouldn't think so otherwise your battery life would be you know wouldn't be great with this thing so not sure what the deal is there anyway you know maybe it just done does the pump you know once every 10 seconds or something like that I'm not entirely sure how it actually operates and then just you know it takes a sample every 5 or 10 seconds or something perhaps now until we actually get down there and look at the labels I don't know which ones are installed in here what different types of gases these are designed for but you can see different types of top elements here this one has got it's weird it's got some sort of I don't know you know rough metallic surface on it almost like it's little globules of solder or something like that I'm sure it's not obviously but that's what me is in the electronics engineer that's what it looks like almost anyway we've got that particular service so it's acting as some sort of filter on top these things are going to be filtered and this one has some sort of membrane filter I'm not sure what that material would actually be this one looks basically the same but it's obviously designed it's a different sensor desire for a different gas they got different colors on them so presumably they're different models and this one here is a complete molded plastic case except for it looks like a tiny little vent hole in the top that's all we got there why so small these sensors these are actually can be blocked by you know water or gross humidity or something like that in the air at least some of them so you just have to be careful not to you know certainly wouldn't want to immerse this thing that's for sure the only way I can think to get these out apart from pulling Emma's give my hey there we go give it a good whack and we're out look at that we got ourselves these these two have popped out our you can see the connectors down in there show you those in a minute there we go and this one down here which is in its own plastic cavity I'm not sure why there we go tada we're in like Flynn feel that uh-huh so it turns out this one with the plastic surround here is different it's got a pinhead it's got a standard naught point one inch pin header it's got a polarity hole plugged up there so that's what this module plugs in for I still don't know what it does is nothing ex sensor so that's intrinsically say sensor C I don't know I'll have to take a close look at that and decode that to see what that is but anyway it looks like there's maybe that one is for like semi-permanent installation it's only plastic but perhaps that's different anyway the other three physically use a smaller smaller pin pitch connectors there and they're male instead of female so in finally different and that's what these sensors plug into and they're plug and play so obviously they've got some sort of ID system on there whether Lubeck there you go I've been to Lubeck fantastic little town in Germany I loved it I went to an organ recital in Lubec there you go one of the churches there that was something yeah so these are rather interesting whether or not they do it with just like a resistor value or something like that you could and the firm we just reads the resistor value that would be the easiest way to easiest way to do it otherwise you could have like a little maxim you know laser engraved ID chip or something like that perhaps or some sort of you know e-squared prime or you know something I squared C cuz you'd only got a couple of pins available there but anyway so that's the real sense of whether or not these have any amplifiers in them at the bottom I guess we'll find out by taking them apart or whether or not they are you know analog output just direct analog output so we'd only supply like a power we'd get analog output and then we'd have the ID the pin ID system whether or not that's the case or whether or not they do actually contain an amplifier and the board in here is expecting you know I correlated like you know a 1 volt analog output or something like that because this thing does actually you know it measures value so it's got to have a DC it's got to be an analog output sensor and it does data logging as well I think I forgot to mention you can actually log data for like 50 hours or something like that so yeah so I might have to crack these open but let's get the rest of the box open first I think now will be interesting to see inside if the PCB is conformally coded or not you don't have to for intrinsically safe our devices although it may be probably not it'd be my guess but certainly would not surprise me if we found a conformally code aboard I don't expect anything fancy a Spector you know an 8 or a 16 bit micro or something like that drive in the LCD and with a ADC either building to the micro if it's not that atom and in a requirement that's a long screw or poor whether or not it uses an external you know precision ADC something like that could very well do I will find out but I don't expect much else I expect a microcontroller on the electronic side of things a microcontroller maybe some signal conditioning that one that one's feeling quite quite we and almost as if it's slipping so I don't know yeah it's not just gonna oh yeah hey there we go we're in took power do that that's pretty easy it's gonna board on the front for the PCB for the LCD I should expect so the rest of this hopefully just pulled out mm-hmm there we go it was just held in with a pin header on the back side of the board there there oh yeah it is conformal e-coated yeah there you go you can see the gloss of the conformal coat so yeah it just had the pin header down in here is the female and down there on the LCD we've got our male pin headers down there which then plug into the board neat so what we've got here is a two board construction right angle Rd 25 as you'd expect so double-sided dot load on that so there's quite a bit of stuff going on on that board but that's a processor as I said eight 16-bit micro maybe some latches or something like that very old-school sort of design so I'm not sure the vintage of this one but might be able to get a chip decode or something like that got ourselves a battery for the battery backup of course for the real-time clock that could be the real-time clock chip there if it is quite old school year as a 32 that would be the 32 kilohertz watch Christel next to it because of course being a data logger you've got over date and time stamp everything and then probably some analog stuff happening on the bottom perhaps but there is a secondary board here I'm not sure if that's just too well shielded look at that they've really gone to town to put the that metal foil all over that that's yeah that's really going to town so I'm not sure if that's part of the intrinsic safety of it or whether or not it has to do with um yeah just a you know keeping out interference for the sensor board so yeah we got some circuitry down on there can see some resistor networks and stuff like that so we're probably oh yeah yeah yeah I think it's going to be chalk or two so there's lots of analog stuff happening on here but I think this is going to be a lot of old-school I probably expect a lot of 7/4 series logic like I'd probably expect these to be you know latches or 74 series latches or something like that perhaps and there's the top side of the board there are this connector here is the pump output so it goes directly up into the pump mechanism in there there we go there's the is the reservoir for it and the pump just drives that boom boom on a offset shaft there and boom it just drives it in and out something like that and generates a bit of pressure whether or not so noisy you wouldn't think it would be you know hugely noisy or something like that so yeah this as I said most likely that oxygen sensor if I can google that part number haha no no no no no knew that's not an oxygen sensor that's going to be a pressure sensor of course making sure that the pressure inside the system is still good here is going to be oxygen sensor I'm presuming once again it's an oxygen sensor they've got that sense of going directly down to the analog board down there there we go tipping header that's a bit that's a bit dodgy and how you do and look at that don't like that G they could have done that a bit better at least have a locking connector or something like that not impressed there and the pressure sensor of course I could get you can look up that number there it is PA 6gf 25 I have no doubt that's a pressure sensor should have known that I used to work on pressure sensors a lot back in the day but that also goes down to the analog board down there nothing special so that's what we've got in the whole system so my guess ambient oxygen sensor plus the plug in units I still don't know what that one down there is with the separate connector it's obviously got nothing to do with this pump system actually no I stand corrected again I've gotten this out and it gets more interesting as we get into this thing as a vertical board here there's some sort of sensible there's another sensor embedded in this part here this is really interesting this is why it needs the pump it needs to flow the air across there Atlit now I still think it is the oxygen sensor but it's really interesting look they've got to mirror it a real like a polished mirror or something in there almost looks like a gold type finish or something like that which is you can see it's sort of welded on the back there so they're obviously there so this I don't think as a sensor this is like the like eight probably and infer aha I reckon this is going to be an infrared LED bounces through there off the back and we've got ourselves a photo sensor here which can detect the oxygen level aha that's what it's got to be just like those cheap-ass ebay pulse oximeters you can buy that tie clip on the end of your finger they just clip on there and they put they shine infrared light through your finger and based on that you can work it based on you know absorption and stuff like that you can work out the level of oxygen in your blood I reckon a similar sort of thing is probably happening in here we've got ourselves an infrared LED transmitting bouncing off the back and then you know maybe you know why that they've obviously gone to a lot of trouble there it's not just a mirror it's a specific type of mirror so specific type of material so whether or not that's doing some filtering or something or some such thing I don't know I'm certainly no expert on that side of things but here's our second board down the bottom here we can pull that off there we go they've got a little flex membrane going there so it's all really quite a bit of a mess going together here so that's only a interface board really nothing fancy there at all but they've gone to a lot of effort to sort of integrate that in to that whole pump system and it just seems very convoluted like they could have easily done something a lot more attractive and sensible than that I would have thought and that plastic ring on that connector there it's just that it's a plastic ring so yeah yeah to stop but presumably to stop the wrong modules being forced into the wrong hole so why they've gone to that effort there's obviously one module which you know they really don't want as part of this modular system it's designed to be plugged into a separate connector what that one is I don't know you'd have to read the user manual I haven't read the user manual and it'd be too much trouble wouldn't it and it would ruin all the fun of trying to figure out all this yourself actually this is getting rather confusing the more I think about it I'm the first thing I'm thinking now is that what why do you need the pump the pump isn't needed just for an infrared oxy meter for example that could easily work without the pump so that doesn't make sense that they would need a pump for that so I yeah I don't know how hey I get it I I just got it I just got it okay yep the where does the pump go look at this bottom here here's the inlet okay this is actually I think this is the inlet up here and that's what ugh din - aha there you go that was our port on the top so there you go that's designed to plug an external probe into it and then of course when you've got an external probe you need the internal pump to suck it into the chamber in here to actually analyze it and I'm also thinking that this is may not just be an oxygen sensor it might be doing other stuff as well I think I barely go to the manual for this one and yes sure enough it all becomes quite clear when you read the manual should do that first RTFM yeah the internal pump is an optional thing which look he's a happy dude there is a check in a remote the hose coming out there and checking a sample port on this pipe here has probably got some stuff Reiter thrilled he's checking whatever you know for the presence of gases or something within that pipe that it's a suitable level and there you go you can draw out 45 meters that's pretty good so there you guys so that answers a question about the noise and stuff like that who cares you know how our quiet is is not continuously operating it's only when you choose the internal pump and they also differentiate between this which yes I confirmed it is an infrared our sensor that was pretty easy and I was pretty sure I wasn't going to be wrong there but this what they call a cat e^x sensor which is the one that plugs into here which is this module here you can choose to switch between these two and they might be the same sensor for the same gas for example or not the same sensor but the same are detecting the same gas you can choose between two different types this one which uses whatever method and the infrared one and there's a page which explains that today here it is IR a X so the infrared one versus the cat so the infrared operates in environs with low or no oxygen AHA and the infrared one is immune to poisoning and inhibiting compounds that effect this poor sucker here so there you go so you can have both of those in there and you can choose well there you go different responses different compounds versus catalytic sensor which is this one here so there you go you can choose during Operation which one you want even though detecting the same gas useful for different environments terrific thought of everything so why don't you just use the infrared for everything well I don't know I'm sure one of these that catalytic sensors is going to be better performing in some situations and as it turns out I believe this one is actually a methane sensor but you can get different types you can get ones that do hydrogen and what's called nonane never heard of it anyway for you chemistry buffs out there it's c9 h20 go figure now I figured out why we've got different sensors here these are well in this case this one's an oxygen sensor there we go oh - and this one's a hydrogen sensor h2 so these are just regular sensors but this one is a catalytic sensor as I said and this one is designed to that's why it's got a different physically different connector on it it needs power for an internal heating element in their design to detect combined combustible gases and this is the e^x sensor see and here's how it works and tada we don't even have to open it this is what is going to be inside the sensor here and it looks like it's fully potted anyway I don't think I'm really going to be able to work get in there properly thankfully Drager have provided an exploded internal diagram fantastic what we've got inside here is basically a catalytic bead sensor and it's based on the pélissier principle where yes it's like a resistance but the resistance value changes with the gas in there so what we've got is we've got ourselves a heating element here and as a sensing element and basically you heat it up to a couple hundred degrees I'm not sure exactly what temperature gets to but heat it up very hot and what it does is actually burns the gas inside that's why you need the flame arrestor here because you don't want it to you know actually catch a light inside there and fly in our flames to shoot out with these combustible gases so that's what they're doing which is funny in an intrinsically safe sensor and intrinsically safe device to actually burn the combustible gas you're actually trying to detect hilarious anyway what they're going to do is burn the gas in there and if of course the more combustible the gas in there the hotter it actually gets it which changes the resistance of the detector element which is a platinum coil and that's pretty much all there is to it it's rather neat I like it and it gets even neater than that the reason that I show it two coils here one's not actually the heater element they're not actually showing the heater in there but one they've called it a compensator element and what that is basically doing is that one is not reactant to the temperature change so this allows them this is are built into a Wheatstone bridge circuit and that allows them to compensate for ambient temperature because they've got the one that changes with the gas the burning gas pressure in there and one that doesn't so that allows them to compensate for that ambient temperature changes brilliant so yes the gas inside here can actually explode because hey we're trying to detect combustible gases they're going to combust right so to stop it yeah they got this flame arrestor here and a center disc inside the thing which basically controls the reaction it stops it blasting out the end here but it also stops the reaction internally so when it does if it does explode it sort of self extinguishes itself and that's why you can use these sensors in an intrinsically safe product designed in a combustible environment yes they do combust it but I do it safe know might see if I can dig open one of these puppies and tada hello what do we got in there ah hmm let's see if we can't hack into that with a pair of side cutters brilliant I've got my hockey pair of side cutters not my good ones and Wow but that was a waste of time don't know what's going on there anyway potted inside there by that that's interesting no I've hanging Oh Oh what is that that's interesting jeez I've never never encountered that before not sure when Tyrael that is no idea anyone got a clue anyway there is a wire hanging off there so look I just broke it cool stuff in there I know look at that there you go that's weird there's a couple of wires you can see them going that's soaked in some sort of well I won't call it electrolyte material but some sort of soaked in something and there's obviously some sort of sensor down in there not sure what right down in there and this yeah that why I was going through to the top of there so anyone anyway if anyone has any idea how this hydrogen sensor works I don't know and unfortunately the PCB down in there is potted as well Oh all right over to the PCB and I'll try and scrape off this conformal coating looks like this one is coming off relatively easy I see an M in there I see the big am I see the golden arches and no it's not Macker bloody Mickey D for you Yanks smackers here so no surprises for finding a Motorola something or other tada Motorola MC 68 L 11 I'm saying well basically it's a 68 HC 11 as you might be more familiar with the L stands for the low voltage version which goes down to wait for it folks three volts oh but back then that was absolutely stunning so are there yeah there you go obviously for battery operation they're using a low voltage version now this is probably all the firmware in here which is in that puppy over there is probably all in assembly language it could be NC but could have been originally written in C but more likely assembly language because to get a product like this certified as intrinsically safe every line of code in this thing must be verified you pay someone like a hundred bucks per line of code to actually go in and verify that it's all ok and it's not going to explode or something like that so yeah I'm so more than likely written directly in assembler and those other chips yeah pass right latches there we go 74 HC five seven fours is that a date code I can see there of the 27th week oh one possibly a number on that one's not easy to make out so get some of the magic spit and put that on there might come up a bit later better let me get the right angle on that and you probably can't read that but I can it's just an NEC memory so yeah that's just coupled to the processor on the other side and just some random ones next door it's 7 4 HC 320 so as I said all these are probably going to be just you know pretty generic out 7 for series logic nothing much happening at all now this array of components down here is quite interesting what I think there's no analog stuff happening here this is another analog latch so all of this stuff is digital so what this is because of its proximity down to the external connector down here for intrinsic safety what they've done is they got resistor limiting and diode clamp in here so that's that's why they've got so many in that symmetrical arrangement near the connector there so all of the i/o go into this connector for intrinsic intrinsic safety reasons is all going to be a resistor current limited and diode clamped and you're going to see the same thing over here with this D 25 connector as well and probably this external external connector here they're all going to have the same arrangement and if we rip apart what we'll call the analog board here interesting they got some marks on there they've done that before it was conformally coded you can see the coding over that so I'm not sure why they're marking that and those because they just look like resistor R raised to me nothing fancy pantsy going on there at all they've got some board some like elephant hide under there hots knotted in place that's interesting that would be for intrinsic safety reasons there's no other reason why they'd have that cardboard in there that's for sure and there we go there's the bottom side of presumably our analog bought find pin pitch part they're fancy pantsy stuff probably just some more 7 4 Hz interface stuff here on top would be my guess yeah yeah that is a four layer board too well that's interesting in a Phillips RP CF 85-77 I squared C interface of course Philips invented that LCD driver so there you go that's driving the big LCD at the dot matrix LCD on the front which is strange because they have a proper LCD module down there with the LCD drivers so huh and it seems that I don't have to scrape the conformal coating off this to see the numbers in there if I get it at the right angle under my mantas microscope I can see clean through the conformal coating straight through the numbers and nothing is revealing we've got three op amps down here just a 27 L 2 s nothing happening just you know jewel op amps these are all 7/4 series logic all around here and it will nothing and all up here so nothing else on the top side there and on the other side here we've got a couple of chord op amps going on once again 27 L Falls there instead of the dual version and some MUX is some 4000 series you know four or five one type MUX is going on around here but that's it so that literally is just an analog interface board really going over via presumably this had a cable here over to the main board and of course there is no ADC on this board or not as a separate chip so it is built into the microcontroller of course this is an e series 68 Hz or even an CL version 68 HC 11e series so it's got an 8 channel 8 bit ADC built in so yeah fairly crude measurements nothing fancy but that's doing all your data logging or your memory over there is holding all your data logging stuff and well yeah there's not much else to it really fairly old school stuff couple of op amps and ADC building to a microcontroller pretty much as expected but of course the most interesting stuff is to be found in these sensors and things like that yeah sorry I can't get that apart and the other one just didn't come apart so yeah I don't know but this infrared sensor rather interesting look they've actually got this is the infrared transmitter here but they've obviously got another sensor in there and another something another sensor happening down in there it's a 2 pin at TI 92 package device just bent over at right angles like that and shoved through a hole in there doesn't come out as a separate hole inside there though well actually that what I thought would be the infrared LED there is not it's got like 4 ohms and also given that looks like a just a bent tio 92 package like that potted in there too by the way they've got some potting compound down the bottom there so can't really get it out intact but I am suspecting that that is a temperature sensor against the against the top metal there that would be that would be my guess about what's going on there because then usually plastic tear 92 packages like that aren't a top entry sensor even if it does have like a transparent or a you know a transparent in encapsulants usually they're on the side they're actually a side emitter so yeah my guess is because they've got the top surface there attached to what basically our thermally coupled through to that metal my guess and being to Penn my guess mmm temperature sensor although there's been an infrared sensor it is quite perplexing because this is obviously a three terminal device whatever is encapsulated in this side of the housing over here and this certainly isn't a lead that's for sure so unfortunately I've had no luck trying to get this sucker out it just won't budge I've taken off the retaining screw clip in there and it just ain't budging incuriously that reflective back in the piece there which is you know some sort of gold mirror or something like that it has got an individual serial number whether or not that's a serial number for the whole unit or whether or not it's just the serial number for that back surface it could be that important that they had two individually serial number and presumably test and characterize that before they actually are welded that in place hmm I just had a thought now I think I might know what's going on here and by the way check this out you can see the angle on that mirror I just noticed that of course because it has to the angle is going to be important to focus it down into the detection chamber down in here what we've got what I think is happening here is that we've got a header element here and that is what some heating up and generating the infrared source we've got our you know our polished and perfectly you know aligned mirror that then reflects that down into the chamber down here and what we've got is a reference temperature sensor down in here a reference sensor presumably and then we've got the actual detector for the for the signal so that's what they're doing it's sort of like a differential between the reference sensor and the temperature sensor under test and then that way you cannot take out any ambient temperature differences possibly I don't know that's my best guess and if you're curious to see inside the battery pack well there we go but I conformally coded are charging PCB down in here which then plugs at right angles into thee that's rather neat I like that and it looks like a we're going to ourselves a baseboard that that's used as the connection the external external connection for power through to the main board so yeah really interesting arrangement really looks like it is charging port on the top here but that looks like it's all gunked up looks like it's totally sealed once again for the intrinsic safety so yeah that's really heavy and probably fully potted so and I think there's any chance of me getting that out anytime soon so there you go that's the dragger or Drago probably pronouncing it incorrectly I'm sure multi warned it's the multi one two actually and that was really rather interesting a bit more involved than what I thought and rather is fascinating so if you got any more details on how say the infrared sensor and stuff like that works and please link it in because that's fascinating but there you go whole bunch of detectors fascinating technology and I'm sure there's a whole bunch of you know really good science behind all this stuff too you could do a PhD thesis on just you know how various different types of infrared sensors there are different types of these different techniques for actually doing it there's an open one which actually works in um open air which is you know much huger than this you know like in the scale of meters and things like that for you know big plants and and stuff like that detection but this is fascinating how that's just you know linked in like that and then you can plug a probe on the top here and you can sniff things and fantastic I like it fascinating technology anyway I hope you enjoyed that and you want to discuss it the eevblog forum is the place to do it the link is down below catch you next time you you

Channel: EEVblog

Views: 69,061

Rating: 4.8921833 out of 5

Keywords: drager multiwarn, gas sensor, gas detector, how to, tutorial, teardown, hydrogen, ozygen, explosive, pellistor, Catalytic bead sensor, Dräger (Organization), draeger, hydrogen sulphide

Id: ph3utXdviAY

Length: 40min 6sec (2406 seconds)

Published: Tue Apr 15 2014