abnormal large noise

[Reinhard]

Hi, all

I'm wondering who has such an experience about abnormal large noise. Our system now has an abnormal large noise level (around +/- 70uV), while it was +/- 20uV previously. One reason I can guess is that our lab was under decoration and now is reopened, the power supply and wires' layout was changed. Could it cause the unstable voltage?

Is there anyone has such a problem before?

Is there anyone tried to use a external voltage stabilizer for a reasonable noise level even using a DC power?

Is there anyone tried to build a Faraday cage to reduce the noise?

[Mary Guaraldi]

We also had a large increase in noise after our lab and the lab next to ours went under construction and new light fixtures and -80 freezers were installed near by. I tried to reduce it using a wire mesh covering and adding additional shielding to the wiring but those did not help. One thing which seemed to help (a little) was to do experiments in the dark after hours. The lighting system was found to cause some of the noise. I have not tried to do any experiments lately but will be back in the lab next month. I hope you find the source of your noise and look forward to any solution you may find.

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[Jon Newman]

Hi Reinhard,

To start, do you have a digital oscilliscope in the lab? If so use it to probe one of the channels form the MEA at the National instruments breakout board. This will allow you to see the temporal characteristics of the noise and will give you hints at its source. 

- If the noise is intermitant, then Mary's suggestion about freezers (specifically its compressor) and lights is a good candidate. See my response to Mary about how to deal with this.

- Generally your ossilisccope can be set to trigger off of Mains power input. If you get a stable noise waveform using AC power as a trigger, then at least some of the noise is being coupled from your AC power outlet. Check for ground loops.

- If you see sharp trasients occuring at 1 kHz to several MHz, then the noise is likely caused by a switch mode power supply that is (1) inproperly isolated from the ground return of its AC input or (2) is emitting strong enough EMI that it is coupling that way. If this is the case, locate switching power supplies (e.g. wall warts and electronic gizmos around the area which have them integrated) and unplug them one by one until you see the transients dissapear on the scope.

- If you oscope has an FFT/spectrum analyzer built in, look at the power spectrum of the waveforms. This will tell you everything above but in a single picture.

--

Jonathan Newman

Postdoctoral Fellow, MIT

http://www.mit.edu/~jpnewman/

[Jon Newman]

Hi Mary,

I'm answering your question separately since it is more well defined. For slowly varying magnetic fields (those below ~100 kHz, such as those generated by overhead lighting, electric motors, trains, industrial requirement, etc), Faraday cages made of wire mesh will be effectively transparent to the offending field and offer no protection. Counter intuitively, you will need to create a shield out of _high magnetic permeability material_, that does not any contain holes like the wire mesh does. The mode of action here is actually not to reflect the offending fields, but to draw them into the shielding material where they are dissipated by loss due to Eddy currents which themselves dissipate as heat. Holes in the shield prevent eddy currents from following and reduce the magnetic permeability of the material, so try not to have any of them.

The easiest way to do this is to get a cheap plastic or cardboard enclosure that completely surrounds your amplifier and spray the entire inside with several coats of EMI nickle-iron (mu-metal) paint such as this

http://amzn.com/B005T8O7X4

Jon

On Tue, Sep 15, 2015 at 6:56 AM, Mary Guaraldi <mtgj...@gmail.com> wrote:

[Mary Guaraldi]

Thanks!

[Reinhard]

Hi, Mary

Thanks a lot, I don't know why but the noise level in our system become normal (about +/-20uV) again. Did you ever have such experience? How about your noise level?

On Tuesday, September 15, 2015 at 6:56:33 PM UTC+8, Mary Guaraldi wrote:

We also had a large increase in noise after our lab and the lab next to ours went under construction and new light fixtures and -80 freezers were installed near by. I tried to reduce it using a wire mesh covering and adding additional shielding to the wiring but those did not help. One thing which seemed to help (a little) was to do experiments in the dark after hours. The lighting system was found to cause some of the noise. I have not tried to do any experiments lately but will be back in the lab next month. I hope you find the source of your noise and look forward to any solution you may find.

On Sep 15, 2015 5:57 AM, "Reinhard" <laos...@gmail.com> wrote:

Hi, all

I'm wondering who has such an experience about abnormal large noise. Our system now has an abnormal large noise level (around +/- 70uV), while it was +/- 20uV previously. One reason I can guess is that our lab was under decoration and now is reopened, the power supply and wires' layout was changed. Could it cause the unstable voltage?

Is there anyone has such a problem before?

Is there anyone tried to use a external voltage stabilizer for a reasonable noise level even using a DC power?

Is there anyone tried to build a Faraday cage to reduce the noise?

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[Reinhard]

Hi, Jon

Thanks for your suggestions, and we have tried to detect the noise at the breakout board shown as the following figures. It seems that we have two different noise sources, one is with high frequency and large voltage amplitude but not continuous, the other is continuous with low frequency but has lower voltage amplitude. However, I do not think they are from the external electrical supply. Do you have any suggestions to improve our system?

On Tuesday, September 15, 2015 at 8:21:42 PM UTC+8, Jon Newman wrote:

Hi Reinhard,

To start, do you have a digital oscilliscope in the lab? If so use it to probe one of the channels form the MEA at the National instruments breakout board. This will allow you to see the temporal characteristics of the noise and will give you hints at its source. 

- If the noise is intermitant, then Mary's suggestion about freezers (specifically its compressor) and lights is a good candidate. See my response to Mary about how to deal with this.

- Generally your ossilisccope can be set to trigger off of Mains power input. If you get a stable noise waveform using AC power as a trigger, then at least some of the noise is being coupled from your AC power outlet. Check for ground loops.

- If you see sharp trasients occuring at 1 kHz to several MHz, then the noise is likely caused by a switch mode power supply that is (1) inproperly isolated from the ground return of its AC input or (2) is emitting strong enough EMI that it is coupling that way. If this is the case, locate switching power supplies (e.g. wall warts and electronic gizmos around the area which have them integrated) and unplug them one by one until you see the transients dissapear on the scope.

- If you oscope has an FFT/spectrum analyzer built in, look at the power spectrum of the waveforms. This will tell you everything above but in a single picture.

On Tue, Sep 15, 2015 at 6:56 AM, Mary Guaraldi <mtgj...@gmail.com> wrote:

We also had a large increase in noise after our lab and the lab next to ours went under construction and new light fixtures and -80 freezers were installed near by. I tried to reduce it using a wire mesh covering and adding additional shielding to the wiring but those did not help. One thing which seemed to help (a little) was to do experiments in the dark after hours. The lighting system was found to cause some of the noise. I have not tried to do any experiments lately but will be back in the lab next month. I hope you find the source of your noise and look forward to any solution you may find.

On Sep 15, 2015 5:57 AM, "Reinhard" <laos...@gmail.com> wrote:

Hi, all

I'm wondering who has such an experience about abnormal large noise. Our system now has an abnormal large noise level (around +/- 70uV), while it was +/- 20uV previously. One reason I can guess is that our lab was under decoration and now is reopened, the power supply and wires' layout was changed. Could it cause the unstable voltage?

Is there anyone has such a problem before?

Is there anyone tried to use a external voltage stabilizer for a reasonable noise level even using a DC power?

Is there anyone tried to build a Faraday cage to reduce the noise?

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[Riley Zeller-Townson]

Reinhard- from Jon's description, that looks like a switch mode power supply.  It could be coming from another device, not necessarily a power supply that is connected to NeuroRighter itself- try unplugging other devices around your setup.  

This also is supported by your observation that the noise appears to go away and come back again- it is possible that someone is unplugging the device, or turning of and on, cause noise levels to change.  

Good luck!

On Fri, Sep 25, 2015 at 4:40 AM, Reinhard <laos...@gmail.com> wrote:

Hi, Jon

Thanks for your suggestions, and we have tried to detect the noise at the breakout board shown as the following figures. It seems that we have two different noise sources, one is with high frequency and large voltage amplitude but not continuous, the other is continuous with low frequency but has lower voltage amplitude. However, I do not think they are from the external electrical supply. Do you have any suggestions to improve our system?

On Tuesday, September 15, 2015 at 8:21:42 PM UTC+8, Jon Newman wrote:

Hi Reinhard,

To start, do you have a digital oscilliscope in the lab? If so use it to probe one of the channels form the MEA at the National instruments breakout board. This will allow you to see the temporal characteristics of the noise and will give you hints at its source. 

- If the noise is intermitant, then Mary's suggestion about freezers (specifically its compressor) and lights is a good candidate. See my response to Mary about how to deal with this.

- Generally your ossilisccope can be set to trigger off of Mains power input. If you get a stable noise waveform using AC power as a trigger, then at least some of the noise is being coupled from your AC power outlet. Check for ground loops.

- If you see sharp trasients occuring at 1 kHz to several MHz, then the noise is likely caused by a switch mode power supply that is (1) inproperly isolated from the ground return of its AC input or (2) is emitting strong enough EMI that it is coupling that way. If this is the case, locate switching power supplies (e.g. wall warts and electronic gizmos around the area which have them integrated) and unplug them one by one until you see the transients dissapear on the scope.

- If you oscope has an FFT/spectrum analyzer built in, look at the power spectrum of the waveforms. This will tell you everything above but in a single picture.

On Tue, Sep 15, 2015 at 6:56 AM, Mary Guaraldi <mtgj...@gmail.com> wrote:

We also had a large increase in noise after our lab and the lab next to ours went under construction and new light fixtures and -80 freezers were installed near by. I tried to reduce it using a wire mesh covering and adding additional shielding to the wiring but those did not help. One thing which seemed to help (a little) was to do experiments in the dark after hours. The lighting system was found to cause some of the noise. I have not tried to do any experiments lately but will be back in the lab next month. I hope you find the source of your noise and look forward to any solution you may find.

On Sep 15, 2015 5:57 AM, "Reinhard" <laos...@gmail.com> wrote:

Hi, all

I'm wondering who has such an experience about abnormal large noise. Our system now has an abnormal large noise level (around +/- 70uV), while it was +/- 20uV previously. One reason I can guess is that our lab was under decoration and now is reopened, the power supply and wires' layout was changed. Could it cause the unstable voltage?

Is there anyone has such a problem before?

Is there anyone tried to use a external voltage stabilizer for a reasonable noise level even using a DC power?

Is there anyone tried to build a Faraday cage to reduce the noise?

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Jonathan Newman

Postdoctoral Fellow, MIT

http://www.mit.edu/~jpnewman/

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Riley Zeller-Townson

PhD student, Potter lab

Laboratory for Neuroengineering

Georgia Tech/Emory University

Atlanta, GA, USA

[Jon Erickson]

Also, maybe I missed earlier in the conversation, but what are you using to power the NR boards and your amplifier?  As shown/discussed on the NR website, batteries are best as they aren't connected to the ac mains.  With my setup, I had originally supplied power from a fairly expensive low noise power supply plugged into the wall.  I saw a lot of 60 hz , and it was worst when the incubator was opening/closing port to pump in Co2.  So I switched to batteries - which I should have done since the beginning - and voila, the power line noise was essentially unnoticeable.