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更多的资料。
60-Hz noise is most often caused by ground loops. I have some specific suggestions for grounding your setup, which should help to eliminate this problem, and you will find further advice in Chapter 2 of The Axon Guide (available in Adobe Acrobat format at Axon's web site. Another good reference is R. D. Purves, Microelectrode Methods for Intracellular Recording and Ionophoresis, Academic Press, 1981.
Here is a quick outline. Use a brass bar drilled and tapped for 1/4-20 screws as a ground bus, and mount it to your air table. Connect this bar to a good earth ground with heavy gauge wire (braided copper works well). Use a separate, heavy-gauge wire to connect each of the following to the ground bus: microscope, manipulator, Faraday cage and computer chassis. Keep noisy power supplies (e.g., computers, monitors, supplies for illumination sources) in a separate rack from your amplifier, or at least separated from the amplifier if they must be in the same rack. Use a heavy, grounded metal plate between the monitor and the amplifier if they must be in the same rack.
The headstage signal of Axon amplifiers is floating. That is, it is not directly grounded until it leaves the amplifier output. You may find noise reduction by connecting the ground bus to the Signal Ground input on the rear of Axon amplifiers. If this is used, then do not make a separate connection from the ground bus to mains ground.
If you are using two separate headstages (from different amps), you should use only a single ground connection in the bath, and connect this single ground to both headstages. Furthermore, the headstage cables form a loop antenna that pick up line-frequency noise; the larger the loop, the better the antenna. Thus, it is best to run the headstage cables closely together, or even twisted together, as they return to the main units. Some researchers also try to keep as much of the headstage cable within their Faraday cages as possible as another way to reduce line-frequency pick-up.
Note the following may be difficult to implement:Unlike the headstage cables, try to keep the headstages themselves separated to reduce coupling. It may help to place a grounded shield between the headstages as well, if possible, to reduce noise due to coupling between the headstages. Increased noise might also result from coupling between the pipette tips, if they are very close together, so try to keep the electrodes as well separated as practical. |
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