HEKA Elektronik EPC 10 USB, Руководство по оборудованию, Страница: 55 / 81

8. Patch Clamp Setup
8.1 Mounting the Probe
For low noise recording, the pipette holder must be attached directly to the
EPC 10 USB
probe. Although
the probe amplifier can tolerate the additional capacitance of a short connecting cable without instability or
oscillations, we find that the dielectric and electrostrictive properties of coaxial cables introduce excessive noise.
In typical setups, the probe is therefore mounted directly on a 3-axis micromanipulator. The
EPC 10 USB
probes are supplied with a plastic mounting plate for mounting on a flat surface. Holes can be drilled through the
protruding surfaces for attachment to a matching plate or other surface. Because of the extreme sensitivity of the
EPC 10 USB
, special care must be taken in grounding all surfaces that will be near the probe input in order to
minimize line-frequency interference. Even one millivolt of AC on a nearby surface, which can easily arise from a
ground loop, can result in significant 50 or 60 Hz noise. A high-quality ground is available at the
GND terminal
of the probe; this is internally connected through the probe’s cable directly to the Signal GND in the main unit.
The GND terminal on the probe is best used for the bath electrode. Nearby objects should be grounded to the
Signal GND of the
EPC 10 USB
.
Important note: Please remember, that the metal case of the probe must remain insulated from
ground.
8.2 Ground Wires
It is a good idea to run a separate ground wire from the Signal GND jack on the main unit to ground large
objects such as the table, Faraday cage, etc. It is best to have the high quality ground wire run parallel to the
probe’s cable in order to avoid magnetic pickup and ground loop effects. This pickup becomes visible only when
the
EPC 10 USB
filters are set to high frequencies; it can usually be nulled by changing the orientation or spacing
of the ground wire from the probe cable.
8.3 Grounding the Microscope
In most cases, the patch clamp is used in conjunction with a microscope; it and its stage typically constitute the
conducting surfaces nearest the pipette and holder. In a well-grounded setup, the microscope can provide most
of the shielding. Make sure there is electrical continuity between the various parts of the microscope, especially
between the microscope frame and the stage and condenser, which are usually the large parts nearest the pipette.
Electrically floating surfaces can act as ”antennas”, picking up line-frequency signals and coupling them to the
pipette. Make sure the lamp housing is also grounded. It is usually not necessary to supply DC power to the lamp,
provided that the cable to the lamp is shielded and that this shield is grounded at the microscope.
8.4 External Shielding
Especially when an unshielded pipette holder is used, some electrostatic shielding of the experimental setup is
necessary to avoid line-frequency pickup from lights and power lines in the room. Most experimenters use a table-
top Faraday cage with a closable front, and lead all of the cables (e.g., from the microscope lamp, probe, cooling
system, ground lines) through a hole in the cage to an equipment rack mounted outside. If the pipette holder
is somewhat exposed, or if the Faraday cage has an open front, a small grounded screen placed near the pipette
holder may help.