NPI SEC-05LX, Руководство по эксплуатации

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Tuning Capacity Compensation
Version 1.11 page 8
Second part: fine tuning
Now the basic setting of the CAPACITY COMPENSATION is achieved. Since the electrode
parameters change during the experiment (especially after impaling a cell), it is necessary to
fine tune the CAPACITY COMPENSATION during the experiment using the CAP.COMP.
control on the amplifier. To get familiar with this, connect a cell model and go through the
following steps (the procedure is the identical with a “real” cell).
 Connect POTENTIAL OUTPUT and CURRENT OUTPUT (front panel) to another
oscilloscope.
 Set SWITCHING FREQUENCY to the desired value (>15 kHz) and DUTY CYCLE to
the desired value.
 Set the HOLDING CURRENT to zero. With the amplifier in CC mode, apply square
pulses of a few nA (or a few tens of pA for patch recordings) to the cell. Negative current
pulses are recommended. If you apply positive current pulses, be sure only to elicit ohmic
responses of the cell membrane, i.e. pulses should not elicit openings of voltage gated
channels.
 The POTENTIAL OUTPUT should show the ohmic response of the cell membrane,
without an artifact, as illustrated in Figure 6 and Figure 7.
Figure 7: Capacity compensation of the electrode inside a cell. Current stimulus and
membrane potential are shown.
Hint : The results of this procedure look very similar to tuning of the bridge balance. If the
BRIDGE is balanced accurately no differences in the potential outputs should occur when
switching between CC- and BRIDGE mode.
Important : Always monitor the OUTPUT from ELECTRODE POTENTIAL OUTPUT at the
rear panel, using a second oscilloscope. The signals must be always square. If not,
CAPACITY COMPENSATION has to be readjusted or the switching frequency must be
lowered.