External noise

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Bubli
Bubli's picture
External noise

Hi everyone,

I was wondering if anyone has found some effective solutions to get rid of "noise."   I'm using a HEKA amplifier and initially I didn't have very much noise on it.  But recently, my amplifer (headstage) is picking up alot of external noise.    The microscope is in a Faraday cage, everything is grounded but there is still some 60 cycle noise and some bi-phasic noise (within the 60 cycle noise) that I can't seem to get rid of.

There is another rig set up in close vicinity to mine, but i don't think that rig is the problem. Does anyone have any suggestions to help eliminate the noise.  Your suggestions would be greatly appreciated.

The FFM
The FFM's picture
When you say that everything

When you say that everything is grounded does each cable that you have going to ground run individually to your grounding point?

Be careful not to plug the ground cables into one another before the ground otherwise you could be making what are known as ground loop and either introducing more noise or perpetuating the noise from one part of your system.

Have you checked that that the ground or earth to which all your cables run is truly going to ground?  In many modern buildings the ground socket of a power outlet is going to a virtual ground and the rig is  not sufficiently grounded when you send your ground to that.  Try and find a copper pipe that runs to earth in the building.  Ask the facilities dept of your institution for the building blueprints if necessary to establish all the true ground points in the building.

Do you have any pumps in your perfusion system?  Are these using an internal AC power source or an AC/DC converter.  Are these power sources outside the Faraday cage and are all cables running from them shielded and grounded?

Using a single powerstrip with the appropriate number of sockets try and get all the power to all the instruments in the rig  to run from one outlet from which you know the noise is a small as possible.  

Bubli
Bubli's picture
Thank you for you suggestions

Thank you for you suggestions . . .turns out the noise was line noise from the equipment . . .we are now using an isolated transformer and it seems to be doing the trick.

engstar
engstar's picture
Use a single powerstrip to

Use a single powerstrip to supply power to all instruments?
I guess that it may be better to supply power to the amplifier, digitizer, computer, Faraday cage and all the instruments inside the cage using one powerstrip, and to supply power to noiser instrments outside the cage such as the peristaltic pump, lights using another powerstrip. I tried it but it made no difference from using a single powerstrip. But theoretically speaking, separate the power supply to the noiser instruments from that to the recording system should be better. I wonder whether there is anything wrong with my understanding.