Axon Axopatch 200B, Theory Of Operation

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GENERAL INFORMATION • 71
Chapter 7
Chapter 7
Reference Section: General Information
Grounding and Hum
A perennial bane of electrophysiology is line-frequency pickup (noise), often referred to as
hum. Hum can occur not only at the mains frequency but also at multiples of it.
The Axopatch 200B has inherently low hum levels (less than 0.005 pA
p-p
). To take
advantage of these low levels great care must be taken when incorporating the
Axopatch 200B into a complete recording system. The following procedures should be
followed.
1) Ground the preparation bath only by directly connecting it to the gold
ground connector on the back of the headstage.
2) Place the Axopatch 200B in the rack in a position where it will not absorb
radiation from adjacent equipment. A grounded, thick sheet of steel placed
between the Axopatch 200B and the radiating equipment can effectively reduce
induced hum.
3) Initially make only one connection to the Axopatch 200B — from the
SCALED OUTPUT to the oscilloscope output. After verifying that the hum
levels are low, start increasing the complexity of the connections one lead at a
time. Leads should not be draped near transformers located inside other
equipment. In desperate circumstances, the continuity of the shield on an
offending coaxial cable can be broken.