Electrical noise

ShivahnShivahn Unaware of her barrel shifter privilegeEastern coastal temptressRegistered User regular
The situation, briefly, is that I'm doing science in a Faraday cage, but have a lot of electrical noise that just randomly started at some point. It happened before, and went away within a week or two, but recently it started again and after a few days I got fed up and started removing things from the cage. It turns out that the bifurcating gooseneck light that I use to illuminate the preparation is causing it. I don't know why that suddenly started, or what. I just got frustrated with removing it to make a recording and grounded both necks, and it's... much better, maybe even usable.

However, it's still somehow generating noise. I know this because when I touch it, the noise decreases even more, but springs back about a second after I let go. I don't think it's just me being grounded (it might be? Not an expert) because when I dip my finger into the grounded solution the prep is in, there is still noise.

Does anyone have experience with this, or ideas on how to fix it?

Posts

  • romanqwertyromanqwerty Registered User regular
    It sounds you might have ground loops (perhaps dodgy shielding inside your gooseneck). See if you can ground all your electrical signals in a way that doesn't create any loops.

    Handgimpa5ehren
  • HandgimpHandgimp R+L=J Family PhotoRegistered User regular
    If you're grounding the cable shield, do it at one end only. Preferably at the source end.

    PwH4Ipj.jpg
    Soggybiscuit
  • SoggybiscuitSoggybiscuit At the edge of spacetime lies a path with no end.Registered User regular
    Handgimp wrote: »
    If you're grounding the cable shield, do it at one end only. Preferably at the source end.

    And inspect any cables with shields. If the cables get kinked in any way, the shield or drain wire can break, which can cause issues with noise obviously.

    Steam - Synthetic Violence | XBOX Live - Cannonfuse | PSN - CastleBravo | Twitch - SoggybiscuitPA
  • ShivahnShivahn Unaware of her barrel shifter privilege Eastern coastal temptressRegistered User regular
    Hmm that makes sense. We have spare cables, so I can try those, and if not I'll see if I can't figure out a way to ground the thing without creating loops. Thanks.

  • BlazeFireBlazeFire Registered User regular
    An explanation for why the noise is reduced when you touch it is that you would be adding capacitance to the system. This will act like a low pass filter.

  • ShivahnShivahn Unaware of her barrel shifter privilege Eastern coastal temptressRegistered User regular
    edited May 2017
    Ok everyone, I've got a new problem and I'd appreciate your help. I've made a diagram since it's a lot easier to show the setup than explain with words:
    UOvqefG.png

    The problem I'm having is not mysterious this time. The two pumps, the intake pump to a small degree and the outtake pump to a much greater degree (probably to do with the type of pump, I'd assume?) add a small-but-damaging amount of noise. The tubing I'm using is just some aquarium tubing - polysomething or other. I can look it up if that matters - it probably doesn't. The ends of the tubing are connected to a much smaller piece of tubing, which I'm not sure the identity of (though I think it's polyurethane), which is what actually goes to the sample dish. The intake line physically enters the fluid, the outtake line does not generally, as it would completely drain the dish if it did. However, this means it's not touching the fluid with the ground, which leads to even stronger noise.

    My question is this: is there a way to ground this properly? Since the materials are non-metallic, I can't just.. ground them. Does anyone have any ideas on ways around this, or some simple trick I don't know because I'm not a physicist?

    I can probably fabricate small things if I need to, though since the dish is glass I can't make many alterations to it directly.

    Anyway, this is my new setup and it has problems, and I'd appreciate any help.

    Shivahn on
  • a5ehrena5ehren AtlantaRegistered User regular
    edited May 2017
    Hm. If your experiment is sensitive enough to where you are doing it inside a faraday cage, it is possible that the tubing itself is propagating a tiny field into your cage.

    My initial guess was going to be the liquid, but you said the outtake tube is empty most of the time...though if the pump is always running it may be doing something weird.

    Since it sounds like your experiment is fairly sensitive, I would ground everything that crosses the cage boundary even if it isn't something that would be called "conductive". I'll say that "conductor" and "insulator" are more like engineering terms and not science terms, so everything is relative :)

    Edit: Oh and also make sure the pump and data collection wire (?) are electrically separated outside of the cage as well. Pumps are hellish EM generators and you may be picking that up instead of something penetrating the cage.

    a5ehren on
    Shivahn
  • ShivahnShivahn Unaware of her barrel shifter privilege Eastern coastal temptressRegistered User regular
    a5ehren wrote: »
    Hm. If your experiment is sensitive enough to where you are doing it inside a faraday cage, it is possible that the tubing itself is propagating a tiny field into your cage.

    My initial guess was going to be the liquid, but you said the outtake tube is empty most of the time...though if the pump is always running it may be doing something weird.

    Since it sounds like your experiment is fairly sensitive, I would ground everything that crosses the cage boundary even if it isn't something that would be called "conductive". I'll say that "conductor" and "insulator" are more like engineering terms and not science terms, so everything is relative :)

    Edit: Oh and also make sure the pump and data collection wire (?) are electrically separated outside of the cage as well. Pumps are hellish EM generators and you may be picking that up instead of something penetrating the cage.

    Hmm the bolded is quite possible, they all come through the same area. Things are shielded, but still. That makes sense.

    The cage is open, it's not like, completely sealed sensitive... but I'm doing neuroscience, so I'm trying to record things that are fairly small (millivoltsish) so even relatively small noise is an issue.

    (worse, what I'm recording looks roughly like a single pulse of a sine wave, so it's really easy to lose it in the noise).

  • romanqwertyromanqwerty Registered User regular
    There's a couple of things it could be which immediately spring to mind.
    With debugging what the noise looks it might help if you could show us an example. Can you do a FFT (fast-fourier transform) of the noise to figure what dominant frequencies it occurs at?


    1) The pumps might produce a whole bunch of noise while operating. Can you physically move the pumps as far from both your sample/cage and your data collection cables/instruments? Make sure they're plugged in on a different power circuit if you can. Does that help?

    2) Can you feel any vibrations through the cables while the pumps are on? Physical vibrations can turn into electrical noise.

    3) Do you still get noise while you pumps are adding/removing water from a vessel right next to your grounded sample (i.e. is the noise coupling directly through the liquid or just close proximity)?

    4)How are you grounding your liquid? What else is plugged into the same power circuit as this ground?

    a5ehren
  • romanqwertyromanqwerty Registered User regular
    Also depending on what your budget is, you could try buying a noise isolator like this (http://www.quest-sci.com/).

    I don't think this is a problem that you can't solve with proper grounding and shielding but at some point it's not worth spending a bunch of time solving problems that you can just buy a solution for.

    a5ehren
  • ShivahnShivahn Unaware of her barrel shifter privilege Eastern coastal temptressRegistered User regular
    edited May 2017
    There's a couple of things it could be which immediately spring to mind.
    With debugging what the noise looks it might help if you could show us an example. Can you do a FFT (fast-fourier transform) of the noise to figure what dominant frequencies it occurs at?


    1) The pumps might produce a whole bunch of noise while operating. Can you physically move the pumps as far from both your sample/cage and your data collection cables/instruments? Make sure they're plugged in on a different power circuit if you can. Does that help?

    2) Can you feel any vibrations through the cables while the pumps are on? Physical vibrations can turn into electrical noise.

    3) Do you still get noise while you pumps are adding/removing water from a vessel right next to your grounded sample (i.e. is the noise coupling directly through the liquid or just close proximity)?

    4)How are you grounding your liquid? What else is plugged into the same power circuit as this ground?

    I'm not at work yet, so I can't answer all of these, but the noise is roughly sinusoidal and I'm 90% sure it's 60 Hz (because it's always 60 Hz, I'm not un-used to noise of that type). I believe the pumps are on a different circuit from the data collection stuff, but I'll have to check. Grounding is to the same circuit as all the scientific tools, different circuit from the pumps and light, and is just a gold pin soldered to a wire that's placed in the sample dish.

    I'll check the rest later today.

    Edit: the problem seems to have been, mostly, that the tubing was coming into the cage via the same hole as the data recording equipment. I've taped all the tubing so that now it runs along the legs, towards the center of the open face where I interact with everything, then up over that, so it's not near any data collection cables (which run along the back and out the side). Trying to shield seems to make things worse. There's still some noise, but it's probably low enough for me to record the EPSPs I need. For everyone's information:

    The outtake pump tubing is definitely vibrating a fair bit - it's a very, very cheap pump. So that might be contributing to residual noise (I dunno how to fix it, it runs along the entire cage and still vibrates). The intake pump tubing isn't, it's a super expensive peristaltic pump. The light and pumps are plugged into a power strip plugged into the wall, while a different outlet is powering a huge power strip that the data instruments and ground all come from. The power spectrum shows spikes at 60 and 120 Hz, though I'm not an expert at interpreting them (it's not trivial to get data from that computer to my laptop, and the computer's not networked). Since the noise at any given point is not quite as big as what I'm measuring, and I can see what I'm measuring even with some noise (since the noise moves up and down with the phenomenon, which is a bit slower than the noise), I've probably got this. Thanks again for all the help, I'm sure I'll need it again in the future (...hopefully not later today, though that's possible if I run the experiment and suddenly nothing works. Trials with petri dishes full of saline seem ok though).

    Shivahn on
  • BlazeFireBlazeFire Registered User regular
    60Hz noise.... that lamp is highly suspect to me. Can you take a reading with the lamp turned off (or even better, removed)?

  • Jebus314Jebus314 Registered User regular
    If your pump is a peristaltic pump, meaning it squeezes the tubing to produce flow, then I've seen a fair bit of noise be transmitted through the tubing. I have no idea what the mechanism is, but I'm assuming it's some kind of static charge generated by the friction of the rollers running over the tubing.

    At any rate you can by conductive plastic tubing, which can be grounded. Not sure if that helps with anything. Also when you have so many grounds I would 100% check for currents/ground loops, or maybe through some capacitors on there.

    "The world is a mess, and I just need to rule it" - Dr Horrible
    a5ehren
  • ShivahnShivahn Unaware of her barrel shifter privilege Eastern coastal temptressRegistered User regular
    The lamp wasn't the source of the noise, that's usually what I check first (and problems started when I moved the pumps in).

    I did not know conductive tubing was a thing, I'll look into it if I have more problems!

  • romanqwertyromanqwerty Registered User regular
    edited May 2017
    If moving the tubes doesn't help much one thing to try is to literally use a different power circuit for the pumps (or light too). I.e. a plug that's on a different circuit-breaker/fuse not just a different socket. I was lucky the last time I did measurements like this, we had had a room on two different circuits. Previously I've connected a power strip to a massive extension cord that I ran down the hallway and plugged in in a different lab.

    60Hz is just mains interference (assuming you're in a country with 60Hz AC power) and it'll also show up in harmonics of that frequency (120, 180 240 etc.) It's probably the cheap pump. Actually, it's probably everything, just with the cheap pump being the biggest contributor at the moment. What happens if you run with it turned off briefly?

    Conductive tubing might help but if shielding it with foil or copper mesh doesn't help I'm not sure I'd expect that to. If it's 60Hz it's probably not vibrations from your peristaltic pump (which will probably appear at whatever RPM it's spinning at) though if you remove this noise you might start to see it.

    romanqwerty on
    a5ehren
  • ShivahnShivahn Unaware of her barrel shifter privilege Eastern coastal temptressRegistered User regular
    edited November 2017
    I wish I'd written how I solved my last problem down. Ugh. Some day I will get my PhD and stop bothering everyone with noise problems.

    Here is the current situation: I have improved my rig by adding three solenoid valves with various solutions and an automatic pump control. Everything is powered by a relay, which is controlled by an Arduino. Suddenly, I am getting nasty noise. I am fairly certain it is coming from the pump, as it only occurs when the pump is on. However, it also seems like it does not occur when the tubing connecting the solenoids to the pump is disconnected (the tubing is filled with a conductive solution, so it occurs to me that I may be inadvertently creating ground loops). Whether or not the solenoids are on doesn't appear to have any bearing on the noise. My basic setup is the same as it was upthread:
    UOvqefG.png

    except now attached to the (other side of the) pump, there are a few solenoids, and they, along with the pump control, are wired into a relay being powered with a 12VDC adapter. And also there's an arduino controlling everything. The noise I get is kind of weird, top trace in the picture below:
    OPSZoy2.png

    It occurs in small bursts, it is in an increasing and then decreasing sinusoidal pattern, and it is 60 Hz. It's a bit harder to see in the picture above, but it generally comes into existence, hits a peak, then disappears, and is symmetrical across the tallest peak.

    Does anyone have any suggestions, and also, does anyone recognize that noise pattern? It's really weird that it just starts and then stops.

    Shivahn on
  • KetBraKetBra Dressed Ridiculously Registered User regular
    edited November 2017
    I am guessing the motors in your pumps are generating noise that is being propagated as low frequency radio noise. How are your data lines shielded? How are your pumps operating? Are they stop/starting or are they continuously operating?

    I am assuming your pump controls are being run independently of your data collection computer?

    I would try replicating your noise by just dry running your pumps with no experiment, but recording data. Leave the pumps running but unhooked and try physically separating them from your data line.

    If it is radio noise being picked up in your data line you can try a few different things, depending on the frequency of the signal you want to measure. You can use a simple RC low pass filter, or using a ferrite clamp on your data line.

    Edit: though, now that I think about it for a second, a ferrite clamp will probably not work for your frequency of noise.

    KetBra on
    KGMvDLc.jpg?1
  • ShivahnShivahn Unaware of her barrel shifter privilege Eastern coastal temptressRegistered User regular
    KetBra wrote: »
    I am guessing the motors in your pumps are generating noise that is being propagated as low frequency radio noise. How are your data lines shielded? How are your pumps operating? Are they stop/starting or are they continuously operating?

    I am assuming your pump controls are being run independently of your data collection computer?

    I would try replicating your noise by just dry running your pumps with no experiment, but recording data. Leave the pumps running but unhooked and try physically separating them from your data line.

    If it is radio noise being picked up in your data line you can try a few different things, depending on the frequency of the signal you want to measure. You can use a simple RC low pass filter, or using a ferrite clamp on your data line.

    You'll have to bear with me - I know very little of electrical engineering, so I might misinterpret things.

    The data lines aren't really shielded (I think - I actually should probably look up the specs), other than starting in the faraday cage. I do know that normally noise isn't really an issue for them. The recording setup is completely independent of everything else. I have a digitizer and various amplifiers and such hooked up to an ancient computer, and then separately, an outflow pump plugged into a power strip, and then separately again, the inflow pump, relay, arduino, personal laptop powering the arduino, and so on. The pump turns on, then runs until I turn it off - this is normally a period of several hours, at least. It's a Thermo Scientific FH100 peristaltic pump, if you want specifics.

    I am currently running a mock experiment like you suggest. I am not sure exactly what you mean by leaving the pumps running but unhooked, could you clarify?

    It seems the noise happens when

    1) the pump is on, and
    2) the pump's inflow tubing is connected to the + junction with the solenoids (regardless of whether or not the solenoids are energized) and
    3) there is an amount of fluid in the tubing between the pump and the dish, though it appears that it does not need to be totally continuous

  • MugsleyMugsley Registered User regular
    Without getting too deep in the weeds in what's all going on, is there a way you can perform this work using syringes of the relevant fluids and quantized volumes? Then you eliminate all the pumps and you don't need the vacuum pump since you know how much fluid you're working with at a given time.

  • ShivahnShivahn Unaware of her barrel shifter privilege Eastern coastal temptressRegistered User regular
    Mugsley wrote: »
    Without getting too deep in the weeds in what's all going on, is there a way you can perform this work using syringes of the relevant fluids and quantized volumes? Then you eliminate all the pumps and you don't need the vacuum pump since you know how much fluid you're working with at a given time.

    It'd be pretty difficult, especially because the main reason for the pumps is to maintain a constant flow rate across the preparation. I can try to think of alternate methods, though.

  • KetBraKetBra Dressed Ridiculously Registered User regular
    edited November 2017
    Shivahn wrote: »
    KetBra wrote: »
    I am guessing the motors in your pumps are generating noise that is being propagated as low frequency radio noise. How are your data lines shielded? How are your pumps operating? Are they stop/starting or are they continuously operating?

    I am assuming your pump controls are being run independently of your data collection computer?

    I would try replicating your noise by just dry running your pumps with no experiment, but recording data. Leave the pumps running but unhooked and try physically separating them from your data line.

    If it is radio noise being picked up in your data line you can try a few different things, depending on the frequency of the signal you want to measure. You can use a simple RC low pass filter, or using a ferrite clamp on your data line.

    You'll have to bear with me - I know very little of electrical engineering, so I might misinterpret things.

    The data lines aren't really shielded (I think - I actually should probably look up the specs), other than starting in the faraday cage. I do know that normally noise isn't really an issue for them. The recording setup is completely independent of everything else. I have a digitizer and various amplifiers and such hooked up to an ancient computer, and then separately, an outflow pump plugged into a power strip, and then separately again, the inflow pump, relay, arduino, personal laptop powering the arduino, and so on. The pump turns on, then runs until I turn it off - this is normally a period of several hours, at least. It's a Thermo Scientific FH100 peristaltic pump, if you want specifics.

    I am currently running a mock experiment like you suggest. I am not sure exactly what you mean by leaving the pumps running but unhooked, could you clarify?

    It seems the noise happens when

    1) the pump is on, and
    2) the pump's inflow tubing is connected to the + junction with the solenoids (regardless of whether or not the solenoids are energized) and
    3) there is an amount of fluid in the tubing between the pump and the dish, though it appears that it does not need to be totally continuous

    From what I can tell there could be three ways you are getting noise in your measurements:

    1) Vibrations caused by the pump being converted to an electrical system by whatever instrument you are using (this depends on the nature of your measurements. Pressure measurements or something of that sort could convert vibrations in this manner)
    2) Electrical noise caused by conduction through your system
    3) Radio waves emitted by external equipment (pumps etc.) that is being picked up by your signal wire (essentially acting as an antenna)

    If you run your pumps without having them physically connected to the rest of your apparatus, you should be able to eliminate 1) and 2). Your noise from radio waves should fall off at 1/r^2 rate so moving them further away from your apparatus should demonstrate whether or not 3) is what is causing your noise.

    This is assuming your data line is carrying an analog voltage and unshielded, in which case it is basically acting like an antenna.

    Edit: the more I think on it the I think it is probably unlikely to be radio waves that low of frequency. What rpm are you running the pump at?

    KetBra on
    KGMvDLc.jpg?1
    romanqwertya5ehren
  • ShivahnShivahn Unaware of her barrel shifter privilege Eastern coastal temptressRegistered User regular
    I think it has to be 2 or 3, since the pump has not changed since my previous recording setup (which worked ok). Moving the pump out of the solution causes an insane increase in noise, but of a different signature (much faster, or at least much less easily discerned without expanding the timescale in the view). I'm not at work now, but the rpm is 14, I think.

  • romanqwertyromanqwerty Registered User regular
    Can you take a bunch photos of the setup next time you get a chance?

  • ShivahnShivahn Unaware of her barrel shifter privilege Eastern coastal temptressRegistered User regular
    Sure, I'll try tomorrow

  • KetBraKetBra Dressed Ridiculously Registered User regular
    I doubt you are seeing direct conduction of current through your tubing unless you're using some really weird plastics.

    The solenoids switching will have a transient response which could look like your signal (a damped oscillation, essentially). Have you tried just switching your solenoid valves in isolation from the rest of your system and seeing if there is a response?

    KGMvDLc.jpg?1
  • a5ehrena5ehren AtlantaRegistered User regular
    60Hz always makes me suspicious of AC electrical noise, though at the tenths-of-a-mV level that could be nearly anything.

    At your sensitivity levels, I would definitely make sure the data wire is shielded (with the shield grounded properly to either the cage or earth ground in your electrical system) after it leaves the faraday cage.

  • ShivahnShivahn Unaware of her barrel shifter privilege Eastern coastal temptressRegistered User regular
    Ok, I can try to get a photo soon (though my phone's camera is broken, so it might not behave). Moving the pump tubing further away has two effects:

    1) when the tubing is no longer in contact with the (grounded) saline in the dish, noise gets very high, and is very spiky (not like the relatively calm waves I posted earlier). However, it looks like it has a similar thing with respect to brief bursts of bigger, then smaller, activity, with what appears to be the same envelope as the noise I'm having issues with.

    2) as the tubing is pulled further away, the noise becomes smaller.

    3) the tubing generates noise when not in contact with the saline even if the pump is off, though it's much smaller in size than if the pump were on.

  • ShivahnShivahn Unaware of her barrel shifter privilege Eastern coastal temptressRegistered User regular
    edited November 2017
    Ok, here is my setup. Apologies for the bad photos and general messiness of it.

    Here is the data acquisition bit. Mostly this is irrelevant, I think. There is a computer to the right, and the cables on the left are coming out of the faraday cage. The one that is passing the signal that is most affected goes up and into the second device from the top.
    RYgCBe3l.png

    Here is the setup inside of the cage. The blue wire going off to the right is the one with the funky signal. It connects to the device in the silver holder on the bottom. The dish is right there. The yellow wire is the ground. The pump is connected to the tubing in the lower right.
    cbJ38Orl.png

    This is the pump, there isn't much to see, really. There is a problem when it is on (sometimes. It's super sporadic). The yellow wires go into the relay; when they're shorted, the pump turns itself on.
    Sml6j3Hl.png

    This is the under part of the cart, where the solenoids and drugs live.
    F1x9H56l.png

    Edit: Additional info: If I disconnect the 12VDC connection, the one that powers the relay, the noise stops. If I short the pump wires manually, causing the pump to go, the noise appears and disappears completely when the adapter touches and is separated from the +/- splitter I have on the end.

    Shivahn on
  • romanqwertyromanqwerty Registered User regular
    edited November 2017
    There's a front to that box that you close right? Because a Faraday cage with a large opening won't work very well.


    Ketbra mentioned it earlier but there's 3 obvious sources of noise.

    1) Anything that runs of wall power is gonna put out 60Hz rf. Any long unshielded wires will act as an antenna for this and pick up noise.

    2) Any mechanical vibration might shake your whole sample slightly. This will also introduce noise. This includes making and breaking new water connections. Each "drop/section" of water is not necessarily at the same potential so adding more will almost always show up in your electrical signal briefly.

    3) Anything that's got a direct electrical connection will also introduce noise into your sample. Sometimes sharing a ground will do that too.



    Your data line looks unshielded which is likely picking up your noise source. Actually everything is, but your noise source is the only one you look at with enough detail to notice. It might be possible to eliminate this source but then you're just going to be seeing the next smallest noise source. The fix is to shield your data line better.

    I see two ways to do this. The easy (and shitty) way or the good (but makes measurements more annoying) way.

    Easy way

    All your instruments have BNC coaxial connectors. These are shielded connectors. At some point this is turned into a unshielded banana plug cable and then runs some distance to your sample. This gives you a large distance to pick up noise.

    You need something like this (https://www.showmecables.com/bnc-female-to-dual-banana-plug-adapter). Plug the top part (signal) into you dish, the bottom part you connect to ground and you use a long BNC cable to go from your measurement instrument direct to this adaptor. Now the only unshielded part of your line is directly in the dish, a much smaller amount of wire to pick up interference from.


    Hard way

    All of your measurements take place in a die-cast aluminium box.

    Here's one I prepared earlier. (https://photos.app.goo.gl/mxoAAYkayoUoEwjb2) Shielded cables connected with the side of this box and are then split off into unshielded lines once inside. There's a big hole in one end with a copper mesh sleeve. You stick you microscope objective inside this hole and then wrap the copper mesh around it. I use a TIRF objective that needs to be really close to my sample, but if that's not the case for you you could probably use a transparent, conductive window instead. Your pump and syringe lines would probably need dedicated feedthroughs. This is probably going to be the biggest noise source in this case but it would still be shielded far better than what you have now.




    P.S None of this addresses source 2) of noise but it's hard to do much about that other than moving the source further away. Your pump isn't on the same table and the source is intermittent which makes me think this source isn't likely at the moment.

    romanqwerty on
    a5ehren
  • ShivahnShivahn Unaware of her barrel shifter privilege Eastern coastal temptressRegistered User regular
    edited November 2017
    Unfortunately, the one bit I am worried about actually ISN'T BNC, but I can look at what it is tomorrow. I did make a makeshift low-pass filter at the point of the DC line split, which seems to help a bit. I spoke with a professor and he said that he's also run into a similar problem (though I only described it, didn't show him the noise) and that his solution was to buy better AC adapters (since it's hundreds to thousands of dollars for low pass filters that actually work for him), so I'm gonna try that as well.

    Edit: I'm not sure the box is an option, unfortunately, since I need to be able to manipulate the sample (or, well, jab it with 100micrometer precision). The Faraday cage DOES close, though it doesn't seem to make a huge difference.

    Shivahn on
  • KetBraKetBra Dressed Ridiculously Registered User regular
    edited November 2017
    A fun quick way to construct makeshift shielding is aluminum foil, which can be grounded with an alligator clip.

    It's not pretty, it's not the best, but it's quick and cheap.

    KetBra on
    KGMvDLc.jpg?1
  • ShivahnShivahn Unaware of her barrel shifter privilege Eastern coastal temptressRegistered User regular
    KetBra wrote: »
    A fun quick way to construct makeshift shielding is aluminum foil, which can be grounded with an alligator clip.

    It's not pretty, it's not the best, but it's quick and cheap.

    What a coincidence, I have a huge thing of it lying right by my rig :P

  • romanqwertyromanqwerty Registered User regular
    Yeah the whole reason we do everything inside aluminium boxes is that no "faraday cage" type structure to work in actually seems to do all that much. The door needs to make good electrical contact with all of the other sides and be quite thick. This makes it hard to find good ones without spending a fortune custom building something. We have to prod, move and add stuff to our samples too. Unscrewing the box lid is super annoying but the only way I've found to get super low noise measurements. It sounds like your noise requirement isn't a bad as ours though, so you might get away with just better shielding.

    Even if the connection on your data line is something else, the same principle applies. You need to shield your data line for the longest possible distance between the sample and your measurement instruments.

    Based upon your observations, my guess is the biggest noise source is the transformers that supply 12V DC to the relay. A better transformer might well reduce a lot of that. If you haven't already you should also try making sure it's plugged in to a different circuit than your instruments. I think the sample/instruments/faraday cage should be on one ground with no loops. Everything else should use a different ground or be floated.

    a5ehrenKetBra
  • ShivahnShivahn Unaware of her barrel shifter privilege Eastern coastal temptressRegistered User regular
    I just want to let everyone know that I have mostly temporarily solved the problem via the most jury-rigged solution possible: I took a soldering iron and a hot glue gun, bored a hole into my saline tubing, glued a wire onto it, then hooked it up to the faraday cage's ground.

    Looking for a good AC adapter is ongoing, but sometimes the solution is to abandon all good practice.

    Mugsleya5ehrenAegisZilla360KetBra
  • a5ehrena5ehren AtlantaRegistered User regular
    Just imagine I posted that meme from Leon here.

    Ground everything.
    Everything?
    EVERYTHING!

    :+1:

    Shivahn
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