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I've always considered Otis to be the most iconic elevator brand, with a very interesting technical history. This door controller is very "Otis". It seems to be well designed at every level with well laid out circuitry, proper input/output protection and no corner cutting.
The controller is surprisingly complex. It's a computer controlled variable frequency drive specifically designed for one application. It can operate on a variety of networks including a proprietary one and CAN Bus, plus accept simple switch signals for use with older equipment.
It takes a surprising level of torque to open and close an elevator door, as the drive mechanism isn't just driving the car door, but also the mechanically interlocked landing door, which has a self-closing bias. Then there are various friction factors like debris in the door track and general wear and tear. But the unit must also be able to detect obstructions and avoid using excessive force to avoid causing injury to users.
To give good torque and precise speed control the controller has an integrated VFD with an IGBT module that converts the incoming single phase supply to a frequency controlled 3-phase supply for the motor.
The classic Otis service tool is a simple handheld serial display and keyboard that will display whatever data the module it's connected to sends it. The menus can be quite deep, and also used for diagnostic and development purposes. A notable warning in the pocket service tool guide says "Warning: This function is used to to monitor and change the RAM memory hexadecimal codes. DO NOT USE THIS FUNCTION FOR ANY REASON!!!"
The unit is designed to self-learn the door operator it's connected to, and work out motor-phase and encoder sequence by slowly trying the door in both directions until it hits a limit switch. By watching encoder movement and switches it can determine position based on door size data entered by the engineer setting it up. During the learning sequence it also displays questions regarding door movement and direction if needed.
The IGBT block looks like it might be a Mitsubishi module like a PS21553-N. If it is then it does require external control from the processor for the phase control. That makes the software in the board's processor quite complex as it has to control the motor phases while also handling network communications.
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Is very interesting not least because it's a otis component. I'm just going going to plug it in fact but because it's made in germany. Which means engineering should be very interesting inside so this is a door operator you've just heard a relay click inside no blinky lights or anything like that it's very anonymous. But it has the main supply going in and it has a variable frequency supply out it's got five connections here it's got the three phases protective earth and the screen and then it's got another connector over here for the encoder with uh screen ground.

15 volts and t1 and t2 that'll be the two center positions. So can count number pulses in the direction. It goes in um and to program. This because.

This is basically a computer with a variable frequency drive you get a serial interface and it's the standard. I'm just going to bring it in it's the standard tool that otis engineers use is this a standard tool is this what they still use these days have they moved on i don't think. It is i think they still use this because there's a lot of equipment like this still in use. And it's pretty much universal.

These units are so programmable. Because as the otus has evolved their communication protocols. They've just made stuff backward compatible. Just so.

You you can use the modules in many applications. And also retrofit them to old equipment so um to change parameters on this you have this serial terminal. You've got the six button input and uh you've got the display and this is normally used for telling this to do uh learning. Things well let me demonstrate i'll just press three it's missing.

A menu. But that's okay uh so let's go to uh monitor and then status and it'll show you its current status. It says working it doesn't know where the doors are because it's the texts are not hitting any of the switches the end of travel switches. But it's got a measurement for the door at this point.

In time of 1050 millimeters travel. Other things um days alive. Let's go look for that so uh let's go to the maintenance days alive. It's quite low.

I get feeling this is a reconditioned unit. Not sure and if i press down to go. It says total cycles. Four thousand which is a nice round figure is also not a high number for elevator doors.

So i'm not really sure the history of this unit uh. If you want to find out the software version um. It is test. And two oh that's a day's alive uh that's the one i've already looked at isn't it.

It is indeed a software let me just uh work this out. This is where i get completely lost in menus. The software dates back to 2007. It's i don't know how old this unit is interesting uh.

The other thing there should be another menu. There is uh three engineer four and this lets you set things well that lets you actually see the status uh maximum motor current 4500 is that i guess that's a stall current that it's going to actually detect and sort of take evasive action around it's very very clever uh pass protect limit three percent stop. Distance. 60 millimeters in position range 20 millimeter gsm position 150 millimeter is that the slowing position.

I'm not really sure lock distance 33 millimeter uh lock speed 5 hertz open and close so you can actually set the frequency of the motor. The rotation of the motor anyway i digress i could just basically look at random menus what we really want to see is what's inside this and this is where really i should unplug it because it does contain spicy mama voltages in here so i shall go and i'm going to leave it for a moment because this i just know because it's a variable frequency drive. It will contain big fat beefy capacitors that are just waiting to end my life. So i'm going to let i'm just going to pause momentarily one moment.

Please i think that's long enough. Although. I obviously won't be trusting discharge resistors as having done the full job uh. The connectors into this are wago or wiggle terminals.

So ramdi. Who says oh i don't trust these because they don't have screw terminals. I've come across them in the hussman and well here's a notice you that's been used them for a long time they have a good pedigree. Let's pop that over there out the way and get these other connectors out before i try and get the lid off these are very close together.

So i'm going to have to use long nose pliers to tweak these connectors out as opposed to just ripping them out by the cable. These are also keyed you see these uh little pins on the top you cut off x number of pins. Then put little blocking uh pins. And things into the receiving connector and it means.

That you can't plug the connector in the wrong position well. I suppose you could if you tried hard enough yes. There must be combination you can do that so i actually in the i used to work in elevators. But like way back in the electromechanical era with a company that also did elevators as part of its electrical engineering work.

But not the electronic ones and i did go into uh otis's office in uh argyle street in glasgow. And i inquired about the availability of work and could have ended up there. But the receptionist told. Me that i'd have to be clean shaven to be considered for work uh and well no and i sometimes wonder was that actually their real policy that they didn't they expected their customer facing technical staff to be beardless or was it just her opinion.

I always wondered that uh so i've got my uh swedish. Little socket set to open this german controller such as europe. What would have happened i think it would get bored. Very quickly it would just because as the electronics of a good shot as the electronics crept in the interest aspect of elevators just got less in a way.

I mean they're more versatile. But um. Because they can do a lot more to electronics well this is a good example of that this is a very clever unit. But in a way i kind of like the old electric mechanical stuff.

It was more challenging don't like technical challenges. Although having said that i mean your average engineer. It says it's got two stickers in this it's got the danger high voltage. It's got the do not open sticker well that's a good example is this going to come off is this going to come off it's exciting.

I'll just put that over there. What do we have what do we have let's zoom down this let's brighten. The image up because let's face it it's not very bright. Now is it because that's all dark and circuit board ish that's better uh.

What do we have we've got incoming filtering here we've got spark gap metal oxide varistors. We've got the capacitors come. Mode suppression choke. We've got a couple of inrush.

Limiting resistors here. What are they um and we've got a little relay. Oh is that really bypassed that really is bypassing. These are inrush limiting resistors to to take the spike off it uh charge.

These capacitors and protect the rectifier which i can see is underneath apparently because i can see the symbols. There and i'm just going to take a look oh i'm going to have to take this apart further hey. What else do i see yeah. I'm gonna have to take it apart further.

There's the igbt module under there yeah we need to see that there's the microprocessor. What else is in the vicinity of that loads of opto isolators for the io and we're optimized leaders here everything is well protected. This is what i would expect a of german engineering and b of otis who are quite frankly to elevators. They're the equivalent of fluke to meters.

They're just like the pinnacle of engineering. When you get to the technical side. Don't like the corporate side much. But i i like the technical side.

You know what i'm going to actually start taking more stuff apart. I'm gonna be cautious here. I still don't trust these big fat capacitors oh uh what's the voltage rating. I just want to see if they're proper death beam capacitors yes they are 450 volts.

So they are death beam capacitors just watch out anti 5g people they're going to kill your babies with death beams. Those who have seen that arseholes video will know who i'm talking about just because it's got a 400 volt capacitor 450 volt. That's worse in this case is this going to fit through look at that they've made a hole in the circuit board. Just the right size for a standard socket isn't that just very german verse spring durst technique as they say or whatever.

It is i probably said that wrong my apologies to the germans. I'm right in the vicinity of the dc side here so i do hope there's discharge resistors otherwise. I'm going to hurt. Oh god look how many screws are here what is that about that is probably why they got two screws here.

I'll work that out later on and what was this designed to take it's going out there. No i'm not really sure was that suppression chokes for the variable frequency drive output. So what this does is the main supply comes in against converged dc. And then it gets converted back to ac on with by basically a six transistor.

I would expect uh almost an h bridge driver. So that each output can be positive or negative. And then the processor controls that it pauses pauses and think the processor's got a lot and it's a lot in its hands. Because uh.

If the processor is actually driving the ver. The very normally you get dedicated processors this might be one of those that is designed for variable frequency drives that may be one which means that it can autonomously have a module for driving those that would be very very interesting and logical. Too here is the screws hopefully it's not smothered in heat sink compound. Sorry for any noise here i would have liked to work for autist really a bit of a fanboy of the old brands.

I don't like the corporate mentality. But they're engineering and they do tend to attract the geeks so it would have been interesting. But it doesn't really matter life went in different directions. And i like the older lynch mechanical lifts.

I like riding on them. As well who doesn't oh a quick quick shout out to beno or bean bino. Whatever his name is benno. Don't change.

The settings randomly in contours like this. It's not a good thing. If you want to work in the lift industry get a job in the lift industry and then you'll not only get paid to be in the lift industry. But you'll get to play with lifts.

All the time and get paid for it what could be better sometimes. I wonder if some of the best engineers are too shy to apply for jobs that they love because they're scared that they won't be good enough. Why is this not coming out. Yet is there another screw that i'm not seeing here sometimes.

There are screws. I'm not seeing or is it stuck down with thermal compound. Not really sure i don't want to use excessive force here. I don't want to damage this even though quite frankly.

I don't need an elevator control pcb. I think it's coming up. I should actually be exercising more caution. Because these capacitors could be charged.

Why is this knocking out is this where i have to pause. Because this ain't coming out. It has that sort of feel oh you know what it might be the fact that the rectifier is kicking at a funny angle and because it's kicking at a funny angle. It's kind of blocking it from coming off let's try that no the rectifiers pop back down again.

Oh there it goes right very interesting so first thing. I'm going to do that is a very odd and very strangely specific igbt module. I mean i suppose it's standard. It's the sort of thing you'd find in generic drives.

Uh. Let's check these capacitors for space let's set this to 700 volts uh d. 1000. Volts dc.

In fact and just probe across that and see if there's any just left. Then no i am safe it should be mentioned unlike the street light death beam capacitors uh elevator ones. I'll just put a finger across that's the final test. You know i'd rather have the surprise when i'm expecting it uh it's worth mentioning that elevators kill babies differently.

They smash them between the doors that's how they work so they don't need the death beam capacitors for that so. What do we have here. Oh. This also answers a question.

I had earlier on about the diodes okay so i was looking at these here these are look like two switch wood power supplies. The chips are the viper 228 are very stereotypical it's a dedicated i think that's a fixed frequency switch mode chip. The transformers are they look proper transformers they have the double insulated windings on them. Which is good triple inch lead.

I think they even call that is basically the secondary winding. The bit supposed to be isolated. It's a bit for all the serial networks and stuff like that and the switch contacts. So you don't want to fry your lyft engineers elevator mechanics.

If you're in america uh. They are have they they put extra insulation on the uh secondaries to isolate now. Why do they have two one will be the five volts for the um processor. Although i'd expect a regulator for that and the other one may be supplying the 24 volts.

I think of multiple voltages and 15 volts. I'm seeing pairs of capacitors here in little inductors. I wonder if each one does two voltages. It does look like it two diodes two diodes these uh must be putting out uh two voltages per switch mode.

I've seen 50 volt. I would expect five or less for that i've seen. 24. Volt.

What's the other voltage going to be and why is it going to be that what's the feedback. There's the uh up to isolators for feedback. They've just copied and pasted this uh module across and what's the little 431 ac. It's a 41a voltage reference chip driving up to isolator for feedback back to the switchboard chip loads of filtering capacitor and dr capacitor very common but quite neatly implemented um that really there is that really doing the resistors the resistors in series for dissipation and they do appear to be going over to that really.

Although it's hard to tell because i think this is a multi layer circuit board might not be they are very prone to having multi layer circuit boards yeah it's multi layer. I think they've got a screening layer at least in the middle it makes it very hard to reverse engineer these um. There is protection diodes on the output side for the opto isolators for the input side as well and current limiting resistors. I would expect them all to have just tons of protection for something of this quality.

There's the uh signals over to igbt are they the must be up to isolation built in uh. There must be a translation built into that that's good because it means if that module blows up it's not going to feed back and block the processor. So what's this other relay for oh that really mate i'm not sure about this. But that really might actually just activate the whole power section.

Here would it do that i would expect the switch would power supplies be powered from this i'm not really sure is that either a inrush limiting circuit or as a or is it a discharge circuit. I wouldn't think it'd be a discharge circuit. It could be wrong. Though because these these will actually pack quite a whomp if you were to touch them.

While they were fully charged it would be a very very bad experience it would ruin your day epic costs. I'm expecting these all to be premium quality capacitors goodness knows how old they are any signs that they've been changed any point. No the soda joints are very clean they look like lead based soda. So everything's gonna be super.

Yeah. That's interesting eh that's more or less it so what we've got. Here what's that admiral two for c. 64 an.

That's a memory chip that's going to store the settings uh right. Say what i'm just going to pause just kind of go and look what this infineon chip is i think that may be special purpose just give me a moment one moment please hmm okay. I took a look at the data sheet. It's it's very big.

I didn't see anything specifically relating though. Although it's a 16 bit very capable processor with all manner of networks including canvas it didn't specifically state it was had a module for variable frequency motor drives and i'm looking at this mosfet module here i don't know what it is i don't want to start ripping off the board. Because that'd be very destructive. And the number is apparently on the other side.

Which is a shame uh the five connections at the side get positive and negative plus. The three outputs and then i'm wondering if this is a fairly intelligent module. I wonder if it's been given information or if it's just a dumb igbt there's a possibility it's actually being sent uh data on direction and sort of speed. I'm also thinking where are the current sensing resistors is that also built into the igbt module.

It's possible that it could be a dedicated module just purely for that task that would make sense given that you know variable frequency drives are so general you know of like every factor is like loads of them. But a very nice design very robust looking design. It's followed all the rules. Which is what you'd expect for something designed in germany definitely something you'd expect in an otis product.

So there we have it that is what the inside of these motor drives look like it's worth. Mentioning that the motor drives have to be very powerful because uh. It's not just uh closing the elevator doors for the car itself as the elevator comes into level it will the doors will lock on to the uh the outer doors in the landing. So the landing doors are also powered open by the car and also they have to overcome the fact that they are biased deliberately often with weights to actually close if the car was for some reason to move away perhaps be manually wound away during a rescue from those doors.

If the car goes away then the landing doors will close themselves. Also the doors could be made of metal. They could be made of glass. And there's also always the friction aspect of the fact that they've got the guide rails with the gibbs going down into them to actually keep them in position and dirt and stuff goes into those and mechanical tolerance and wear and tears just they have to be powerful.

This is why it's got a three phase motor and all the current sensing uh so it can actually properly deal with just every scenario. But there we have it well worth looking inside quite an interesting device very text to book in a way. But nicely implemented.

10 thoughts on “Exploring an otis door controller”
  1. Avataaar/Circle Created with python_avatars Eric says:

    Baaaaaaaahco 🐑 are good tools 🛠🤣🇺🇸⚡️⚡️⚡️

  2. Avataaar/Circle Created with python_avatars Mark Harris says:

    With all these mentions of 'Otis' I’m going to have 'Hard To Handle' as an ear worm all day now.

  3. Avataaar/Circle Created with python_avatars Erik Swiger says:

    It might be fun to find an old elevator logic board with relays, before the age of electronics.

  4. Avataaar/Circle Created with python_avatars SeanBZA says:

    Bearded was her opinion, she did not like your accent. Otis techs by me almost all will have some form of facial hair, the only constant is being able to climb up 20 floors with a toolbox.

  5. Avataaar/Circle Created with python_avatars Hola! menno duk says:

    Is there a reason the different modules aren't on different boards so that if some component breaks you can just change that part?

  6. Avataaar/Circle Created with python_avatars Alexis Starsmith says:

    LMFAO!! Death caps 😹 I've handled so many, consider 40oz energy drinks? Yeah them barely fit your meet hooks & potentially lethal!! Still have "CaN capacitors" laying around – imma 2x check there discharged l!!
    Lightning in a bottle type

  7. Avataaar/Circle Created with python_avatars Slikx666 says:

    No schematic today Clive? 😆👍
    Hope you're managing to stay cool, I'm melting. 🥵

  8. Avataaar/Circle Created with python_avatars Keith Davis says:

    I lived in Reading in the 90’s and occasionally I’d see one of their company vans with their office address on the side. Yes, “Otis, Reading” – always raised a smile 🙂

  9. Avataaar/Circle Created with python_avatars WhyteFyre says:

    If I'm not mistaken, the infineon chip is an fpga. Think of it as a programmable logic array specializing in one task, in this case, elevator operation. It's different from a general purpose cpu found on arduinos and raspberry pis

  10. Avataaar/Circle Created with python_avatars 6581punk says:

    Follows all the rules because it's made in Germany? VW didn't oops.

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