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Sunday, February 10, 2019

Keithley 7013-C relay card headless operation

    This will be just a quick post of one things I've been woring on. I have a lot of stuff on the back-burner and about 4 or 5 really interesting blog posts that await to be written up. unfortunately there's a lot of work that has to go into the experiments for those, so bare with me.

   Now that I've made my excuses, here's what I came up with, for using a Keithley 7013-C relay card as standalone.

   It's not that  complex, but it kind of took a lot of time just because of the metric ton of soldering I had to do on the LEDs and wires and also because the modifications to the existing equipment was quite complex. A lot of cutting, filing and drilling... you know, the fun stuff

I got this relay card really cheap but don't have the Keithley DMM for it. It's for a Keithley 7001 Mainframe scanner, but I don't have that neither do I want to buy it. So I decided to put together a platform that allows me to take advantage of the realy card and use it to take measurements of....well, electrical stuff.

   For those curious, you can find all the specifications and schematics in this link.

  The guts of the card are pretty simple. Three  serial shifters, UCN-5841A and, of course, the relays.
   Keithleys are strange beasts, so together with the normal 5V DC supply, there's also a 14.6 V and 6 V rail.... go figure. Nothing some LM317s can't handle.
Note to self... make sure the voltage diciter on the LM317 meets the minimum current load (~10 mA works best).

  The unwilling donor is a piece of  old 19 inch rack mount Philips video equipment. The card slots are almost the right length to fit the relay card in. Almost...
Which in home-gamer talk, that's "take out your rotary tools".

  The front panel was the first to get the make-over.

   I gutted the donor, took out one whole card and took off the components from a second one, so that I could use that as a platform for the miscellaneous stuff I needed (wiring, power supply). I also made everything as modular as possible, with connectors everywhere, so in the future, if I get any more bright ideas I can implement them quite easily.....that, and it makes sense to quickly undo connectors instead of hard soldering stuff together, in case of some unhappy misshaps.

    The transformer secondaries were made for 12V DC operation, so I had to series two of them for the 14.6 V DC rail. Not ideal, but the current demand isn't that high so there should be minimal power dissipation. After about 30 or 40 minutes of playtime with the thing, turning relays on and off, none of the linear regulators got warm, so I guess my hunch was correct. I also did multiple 12 hour runs and everything is still OK. Even a blind dog gets lucky sometimes...

   Those LEDs on the front panel that I showed are to have a visual guide of which relays are doing what, so I also modified the card  itself and added a connector and wires to the shift register outputs. 

Remember kids, 5 minute epoxy might seem handy, but it's a piece of crap. Don't use it. Use the normal epoxy. 5 minute epoxy has a tendency not to stick well and just ruin everything afterwards. Either that, or use Araldite epoxy.

   And of course the drivers for the actual LEDs:

  I organized the whole thing in 2 rows, 10 LEDs each. The botton row is attached to a big PCB that also has the hex buffers on it. The upper row is just stuck on a small piece of protoboard and a ribbon cable going from that to the other board.

   I used a plethora of hex buffers, basically what I had lying around. I think it was two 74LS04, one 74LS19 and something else I don;t remember right now. I'm not really picky, as you can see. Anything goes.

    Of course, nothing is as simple as it looks. The relays are wired in what might seem to be a weird way to the shift registers. For example,  outputs 1 to 4 on the last shift register are wired to channels 1 to 4 but outputs 5 to 8 are wired to channels 8 to 5. So basically the second nibble (last 4 bits) in the first byte (order is LSB to MSB) are reversed. This also goes for the other two shift registers. Confusing? Here's something to help explain  it better

  Also, just a quick mention.. with so much wiring flopping around in the breeze, I used ETFE/PTFE  insulated wire, because it's a given that at some point you'll touch some wires with your soldering iron. It saved me a lot of headaches, let me tell you.

   The controller software, running on an Arduino, is not necessarily the best, in terms of efficiency, but it gets the job done. There's two main parts to the whole thing:
 - The input command handling part
 - and the actual data output to the shift registers

The command handling part isn't really SCPI standard, but I thought this is the easiest way to implement. Strings on  Arduino isn;t the simplest thing to get working well.

A command can be either for a single relay:

or multiple commands

The ";" at the end of a command is a must, in either of the two formats. The SW doesn't throw  back invalid format errors (yet) but nothing will happen if the romat isn't right (as far as I know)

The data to be shifted to the SW is first decoded from the input command, then stored in an array,  Relay_ch[]. From here, because of the way things work with these shift registers, the data gets switched arround into Relay_ch_toSend[] the finally out of the Arduino;

For the actual signals that go to the registers, this si how it happens:
  Data pin set either high or low, depending on whether  Relay_ch_toSend[] is a 1 or a  0. Then a clock pulse is sent in order for the data to be input to the register's register. (I actually  meant to write this)
Once all the desired serial data is loaded, a Strobe pulse will load it into the output latch register and then, pulling Enable low will activate the outputs of the registers.

   Because the PC needs to interface with mains-connected equipment, I've isolated the digital lines using some 4n25  optoisolators. The turn ON time of these is quite OK, but the turn-off...well... let's just say that the Arduino waits around a lot, in software. Hence thosewait times in the software in between switching  the data and clock lines.

  The first test I did was to measure the leakage of 5 wet tantalum capacitors with my Fluke 8505A. Probably the relays are not too well suited for this, but the results are more or less consistent. Did 3 12 hour test runs, after the caps were  formed @10V for at least 24 hours and both the Arduino and Keithley relay board behaved flawlessly.

As always, this is the link to the pics I have for this project. Enjoy

Wednesday, October 17, 2018

Edwards E2M12 Vacuum Pump Teardown and Overhaul

   High vacuum is one of those things that really suck.... Sorry, couldn'd help it. 
  Parts are expensive, finnicky and not always readily available to anyone.

    I recently bought an Edwards E2M12 vacuum pump for a project of mine. When I got it, it came without any oil and without any idea of the state it was in. But for the money I paid, I couldn't just pass it.

   So, I now have a vacuum pump... what now?

Well, to be able to make it suck in the proper way, I needed to give it an overhaul So first thing's first.. get an overhaul kit. How hard can it be?

  Well, very hard, apparently, unless you're a company. Very limited opportunities for those of us not blessed with a VAT number.
Most of the suppliers out there, including Edwards themselves only sell to companies and the only source for the kit I found, charged a hell of a premium for it and asked a metric ton of money for shipping something that weighs in a couple of hundred grams.

As reference, here's a list of stores that have Edwards supplies and kits, together with my rants comments

  • This is where I bought my kit from. A bit over-priced, but least they sold me one They do deal with individuals, not just companies, so that's perfect. However the shipping was very expensive even from the USA to Europe. Also, 0 points for customer support. I litterally tried calling them tens of times but nobody answered. Also all my emails sent to them requesting some info about the order went unanswered. But hey, they don't need to answer any phones or mails when they get a wad of money from their customers

  • Yep, they also have kits and yes, they do do business with individuals, but they're even more expensive than the previous guys.And shitty shipping policy. If you're from the US, they're...ideal. If not, tough cookies then.

  •  European store from what I can figure. Pretty low prices, but they only deal with companies. Only found out after about a week of trying to get someone there to look into why my account was not active. Though if you can borrow a friend's VAT number, they have the lowest prices as far as I've seen.

  •  A lot of supplies  here. Regarding my kit, they only had it from some off-brand company. Not original from Edwards. Could be helpful in a pinch, though.

    Was wondering what happened to all 4 of my mails and the 10+ phone calls or so. But the EM12 kit is finally here. Now what?

  Well, easy if you know you way around one of these things. Not so much if you're a noob like me. So, we seek the help of the collective hive mind.

   This helped me out a great deal. Nice write-up, and a lot of other useful links and info in the posts. Seeing how many models of these vacuum pump are out there, I thought I'd post my own adventure together with some helpful pics. Be sure to have a look through all the posts on the  EEVBlog link before you start working on your pump.

    First thing's first: flush out the pump. That is, drain whatever  oil there is in the pump then fill it with some cleaning fluids. Paint thinner is recommended in the link above, but I couldn't find anything useful, so I used some denatured alcohol. It doesn't do a great deal to dissolve the oil but it does flush out any dirt and in my case, spider webs and is safe on the seals. Of course, the E2M12 is well made and no ball bearings inside to screw up with aggressive solvents. But I went the safer route.

   Yep, guessed it... the blue stuff... denatured alcohol. Even after this step, there will still be oil left if you plan on tearing down both stages of the pump So have a lot of rags on hand or have a big sheet of plastic on your work table / space. I had a big plastic tupperware lid on the table, so it'd catch any oil spills.

Next step would be to get some service manuals for the pump. You can also find those in the previous link. As a side note, the M2, M5, M8 and M12 are functionally the same.

    If you plan on taking this thing apart, make things easy. Separate the motor from the pump first. This will make everything much easier when handling.  Start with the two red plastic parts either side of the pump.

On mine, the coupling to the motor  has two keys on either end of it and two grub screws (#1 and #2 in the pic below) Undo both of these and then the four  Allen bolts holding the motor to the pump's frame.

    Then you can just pull the motor away from the pump. 2 people are ideal for this task, but being the proud engineer that I am, and also being alone in the house, I did it by myself. 

My pump didn't come with a plate underneath. If yours has this, also undo the bolts holding the motor to it.

    Putting aside the motor and focusing on the pump itself, undo the four allen bolts holding the pump cover....after you've drained everything from the pump, that is.

You can use a plastic or wood shim to pry the two halves apart.

   Now that you're in like Flynn,  how about you take off that thin steel plate held with those two allen screws.

    And, while you're at it, undo the other two and the small aluminiun block holding that copper pipe (gas ballast tube) in place. Slide the cast rear cover plate down about 1 or 2 cm and slowly but firmly pull on the pipe. It comes out easily, just be sure not to bend it too much. 

Once the plate is off, you have access to one of the pump's stages.

    If you want to go ahead and take out the vanes, a word of caution. They're made out of some kind of phenolic resin so do not grab then in any way. Handle them like you would one of your french girlfriends.  
   I, on the other hand, took a dental pick and pried them out by hooking onto the spring inbetween the vanes. Another way to do it is also mentioned in that link from EEVBlog... take out the screws holding the pump stage (LV stator) to the rest of the body and slide it out a bit. 1 cm should do it, then push it back in. This should expose the vanes just enough so you can get them out.

Sources mention there is also a bolt in the middle of the now exposed shaft. Mine didn't have something like that. Seems they modified the design through the years.

 So all I had to do to get to the next stage was to only undo the allen bolts of the LV stator. The alignment to the main body is ensured by two precision ground  pins. Easy, right?
Well, it depends. This is the actual tricky part of the whole thing. The mating surfaces of the two parts are machined and can actually stick together.

    There's two recesses in the pump body, one on each side (marked with yellow). You can use those to prie open the parts. Just don't do it with metal tools; use plastic, wood or like I did, aliminium. Even with the aluminium I was extra careful not to scratch the inner surface of the parts. And used them only up untill the point the plates were separated enough to allow some plastic shims in between them.

    Also, the guide pins (marked in...yellow?...lime green?) will ensure the plate jams if you do not pull it out  straight

    These are some of the tools I used  in taking apart the plates. And yes, that's a PCB you see there. I filed down one corner thin enough to get in inbetween the plates and spread them apart. The orange shims were also used fot this task to take over where the PCB left off.

    At this stage, my pump looked pretty clean, so I didn't go any further. I just replaced the seals and started to put everything back together again.

    Also note that there's a lot of service manuals from Edwards from different years and the actual numbering on the schematics is not the same, only the names of the items. So be careful if someone refers to parts from schematic numbering instead if actual part numbers.

A few O-rings and some tightened screws later, everything was back together again.

  Oh, yeh.. you might have noticed the Edwards Pirani gauge on the pump. A little something I picked up on eBay. Works too... imagine that. It's an APG-M gauge and like the pump, it has its own story. But I'll tell that somewhere more private. Like in a next post.

    All's well when it ends well....ish..

 I measured the vacuum level after I put the pump together and the fact that it make any is a real surprise to me. Looks like I'm not all thumbs. But it barely makes 1 x 10e-2 mbar, which is OK for now, but way under the expected performance of this pump.
I think I narrowed it down to some leaks in the gas ballast circuit... probably didnt istall that allast gas pipe correctly. I'll get some vacuum grease and put a dab on the orings and will post some updates. 

As always, this is the whole album of the teardown. Enjoy

Friday, July 13, 2018

Making drafting pens great again. Rotring Rapidograph refurbishing

     Great title, huh?

  Ok, so in a previous post I showed off my drafting pencil collection and wrote some personal notes of what I think about the Rotrings, Pentel and Kuru Toga.

   Now it's time to show you another, more dark part of the involving black drafting ink (Pulitzer nomination for this posting, I guarantee it)

  I mentioned in a post a while back, that I found some Rotring Rapidograph ISO pens at a flea market. So I bought them, took them home, 'cause where else might I take them, then researched on how best to clean them and get them working again. Well, almost every article out there says you should soak them in some water for a day or two. So I did.

    From the black stuff floating aroung, you can guess these pens were ridden hard and put away wet. As you might imagine, this isn't really the way to handle these,  so after pulling on the pens so hard that I thought I'd break the plastic threads on them, I got the tips out and soaked them for 5 days in plain water. And same for the used ink wells. I'm stingy like that.

  After repeated soakings, then tapping the botton on the table (really hard) to get all the crud out, then more soaking , I reached a point where I thought they were clean. But I was wrong....

   So this is what a tip looks like. This is a 0.5mm one. And a dirty one at that. The brown part is the actual tip that goes in the pen and the ink covered thing with the needle on the left is the plunger that goes inside the tip. And as you might have guessed, all that dried ink shouldn't really be there. So I continued with more soaking and  then cleaning the plunger with paper towels. The tip also went for another soaking.

I even tried to put them in some IPA for a few hours (I'm refering here to isopropanol alcohol, not beer)

Better, but still not there. The more I soaked them, the more dried ink came out in small little bits.

   So the only thing I could do was just to keep at it until everything was shiny and clean. This tooks in total 7 days. 5 days of soaking and a whole weekend for the cleaning and putting everything back together.

After I gor everything squeaqy clean, assembling them was really easy. Add some ink cartridged from Rotring and job done

  Now, there might be other like-minded people out there, so what follows is a step-by-step on how to take apart a Rotring for cleaning. Yeah, there's Youtube.... but unfortunately I never really saw someone actually take out the plunger from the tip. Hell, I didn't even know it was there. Imagine my surprise when it first came out of the tip. 

   Oh, and most of the videos show you the pens being rinsed with some water....then lighly dried with a towel. Well, ink that's beed dried for some years isn't really going to dissolve in water. Trust me on this one. The only good way is to wack it out of there.

   First unscrew the pen and the well from the outer casing (the red thing that says Rotring on it)

 Then unscrew the coller so that you're only left with the tip and the ink well

   Now, to pull out the tip, screw it in the back of the casing, then pull on the ink well. Note, that if your pens were like mine and had the ink  dried on it for some years, it'll take a lot of force to pull off the ink well. And by a lot I mean you'll get that "this thing is going to just break in my hands" feeling. 

   But don't worry.... if you pull on it a bit at a time, it'll come loose eventually. As an alternative, you can pull off the ink well just a bit,  then soak the whole tip in some water for a few hours then try again. 

 Nearly there. There's one more thing to take care of. See that little black thing on the end of the tip? That has to also come off so that you can take out the plunger inside. Of course, if you have the ink caked in there, you'll need a lot of soaking and percussive maintenance until you can get that out.

And I leave the rest in your capable hands. After everything is as clean as your OCD will allow it, just put everything back together again. Oh, and don't forget to let the tip and plunger thoroughly dry.

And as a final word, make absolutely sure that every bit of dried ink is gone. If not, it'll just clog up the tip again. Though if that happens, you can use the plunger and ram it from the front of the tip to get  things flowing again.

   See you guys next time. Well, not see you...but... well, you know what I mean.

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