Dagan IX2-700 Manuale operativo - Pagina 10

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IX2-700 Dual Intracellular Preamplifier

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.