Dagan IX2-700, Руководство по эксплуатации

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IX2-700 Dual Intracellular Preamplifier
9
COMPENSATING FOR THE CAPACITY
The capacity compensation control provides capacitance neutralization, or
“negative capacitance” at the headstage input. Without this compensation, high
frequency signal components from a high impedance source such as a
microelectrode would be lost because of stray capacitances at the input. Apply a
square wave (such as in balancing the bridge) to the electrode. Since you have
already balanced the bridge, there should not be a step pulse on the voltage trace of
the oscilloscope. What you will see, however, are capacitative transients at the
initiation and termination of the pulsed current. Turn the capacitance compensation
clockwise until these are at a minimum without overshooting, ringing or
oscillating.
IMPALING THE CELL
With the system calibrated, the electrode in good condition, and the
amplifier compensated, you are ready to penetrate the cell. As the barrel of the
electrode enters the tissue, further adjustments of the capacitance compensation
may be necessary.
As you approach the cell and the electrode tip is abutted against the
membrane, you may wish to use the Buzz feature to aid in penetration. Both
Channel 1 and Channel 2 are equipped with Buzz circuitry of variable amplitude.
The exact configuration and parameters with which you “buzz” your cells is
something that must be determined individually for your particular system. The
type of cell, electrode resistance, and nature of dissection are all factors affecting
the ideal parameters. A bit of trial and error methodology must be employed here.
Finally, the Holding Current may be set at the desired level and the Step
Current Command or an external command current can be directed to that channel.