electrical noise

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lazy
lazy's picture
electrical noise

I have a problem of noise (>20 pA, >100 Hz) which is not AC origin (not 50/60 cycles). I have a good faraday cage grounded. This cage can work against the AC noise, but not that strange noise.

I found over the wall that there is a big freezer. However, I cannot change the place of both freezer and patch setup.

I did all what I know, but I cannot solve this problem. If you have the similar experience, I would appreciate for your advises. What is the possible causes and how to get rid of such noise problems?
Thanks.

Fraser Moss
Fraser Moss's picture
Do you run a ground cable out

Do you run a ground cable out of the back of your amplifier and from the Faraday cage to the ground/earth socket of a wall plug socket?

I had a similar bad noise problem a while back and found that the wiring in the wall of the lab was not properly grounded and so therefore neither was my set up. Only through trial and error of each socket in the room and in the end, a VERY long cable going to a socket with true ground did the problem resolve.

Also if you are using a UV lamp to illuminate positively transfected cells to patch and the lamphouse is inside the Faraday cage, double check its heat sink and shielding.

ecolechio
ecolechio's picture
If you are still having the

If you are still having the problem, you might be able to use a copper screen to shield your equipment.

SimsTina
SimsTina's picture
Hello,

Hello,

I saw your post regarding electrical noise and was wondering if I could ask a question.  I am new to "Scientist Solutions" and am looking for help.

I have an experimentation set up using a force gauge.  When the system is at rest, there is no noise.  When a small force is applied to the gauge, noise is present on top of the force signal.  Because the forces I am working with are small (fruit fly muscle, milli-Newtons), I cannot get a good reading of the true signal through the noise. 

I have tried various grounding techniques and have a "hum bug" in line, a device with filters 50/60 Hz noise, but it does not filter this noise, when the gauge is under pressure.

Any feedback is appreciated.  Thank you, ~Mia~

The FFM
The FFM's picture
 What's the frequency of the

 What's the frequency of the noise?

SimsTina
SimsTina's picture
Hello FFM,

Hello FFM,

I do believe it is 50/60Hz noise because it is cyclic, but it does not have a nice wave pattern on the oscilloscope.  Because the force gauge is very sensitive, the believe vibrations in the room throw off the nice, sinusoidal pattern. 

The noise I see, the peaks are smaller than the valleys but, like I said, it is still cyclical, even if it is a little "craggy." 

And it is only when force is applied to the gauge.  When the force is backed off, the nice 50/60Hz signal returns for a brief moment, until the hum bug senses it and filters it out. 

The FFM
The FFM's picture
Have you checked that the

Have you checked that the grounding on your set up really does go to ground?

The wiring in many labs is such that the ground pin in a socket is actually a "Floating Ground" and this will not satisfactorily ground the circuit and a cyclic hum will develop in the system.  If you have more than one electrical device in the system and they are connected to different power outlets you could also be developing a harmonic mains hum.

The first step would be to acquire an inexpensive circuit tester and check all the outlets in the lab to see if they are actually sufficiently grounded (www.acmehowto.com/howto/homemaintenance/electrical/grounding.php).

If none of them are, you may have to get drastic.  You will need to hunt around for a cooper pipe or something that really does go all the way to ground and hook up to that.  If you are in a university, ask the buildings management for plans of your lab and find out where the pipes and wiring go.  You want something that has an uninterrupted path to the ground floor/basement and literally connects with the earth.

lazy
lazy's picture
I saw a patch clamp setup in

I saw a patch clamp setup in the website of the below. (and not only them, but also some other labs use no Faraday cage).

As you see, no Faraday cage. And I believe they do not have any noise problems. While, I have an electrical noise problem (not AC) even I have a good Faraday cage grounded.

http://research.nki.nl/jalinklab/Equipment.htm

If the microscope itself plays Faraday cage (some one told me like that), we need not Faraday cage which is very helpful. I tried, but in my place, it does not work. I have a huge AC noise when outside the cage.

How t hey can be free from AC noise without Faraday cage?
Thanks.

   

The FFM
The FFM's picture
They probably removed the

They probably removed the cage so that you could see the equipment when they took the picture, or the photo was taken before they put the cage up when building the setup for the same reason.

There are plenty of wires running to ground from everything else in the set up.

neuro
neuro's picture
i have eliminated our 60 hz

i have eliminated our 60 hz noise without using a faraday cage, simply by making sure that all components are connected to a common ground (and not grounded twice... once via the power supply and a second time by a ground wire direct to the ground source).  if you're getting 60 cycle noise, first make sure that there is only one ground source in your bath solution (ie take out all stimulating electrodes).  then individually unplug/disconnect individual components/lamps/etc until you see a noise reduction.  when you find the culprit, reground that item properly, check the position of the component and adjust if needed, adjust position of wires accordingly.