Dynamic Test / Frequency Response; Carbon-Fiber Electrodes - NPI VA-10X Operating Instructions Manual

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Dynamic Test / Frequency Response

For this test a good signal generator with a ramp (triangle / sawtooth) output and an
oscilloscope is required.
 Connect a 1 pF capacitor to the electrode BNC at the headstage. To this capacitor connect
a triangle wave generator, with approx. 0.5 V pp and 20-100 Hz.
 This ramp is transferred into a small current following the formula:
Ic=C*dU/dt.
where dU/dt is the slope of the triangle signal (V/sec).
 Observe the current at the UNFILTERED output using an oscilloscope.
Note: The observed current is always double since you change from a positive (+) slope to
a negative (-) slope [x- (-x) = 2x)].
Note The amplitude of the current is also influenced by the accuracy of the capacitor and
the connecting wires.
 Start with AMPLITUDE and TIME CONSTANT turned into the left most position
(counter-clock wise) and increase first AMPLITUDE and then TIME CONSTANT by
turning the trim pots clockwise. By changing the amplitude and/or frequency you change
the dU/dt, and so you can evaluate the range of linearity of the amplifier and also the
frequency response.
 The BOOSTER is set correctly, if the current output is as square as possible. This also
depends on the quality of the triangle wave at the 1 pF capacitor.
 The effect of the gain stage and filters can be tested easily, if these tests work.
Gain stage: When testing the DC accuracy (see chapter 0) change the setting of the
GAIN and observe the correct signal magnitude at the output BNC.
Filter: If the booster is set correctly connect the oscilloscope to the FILTERED output
and change the filter corner frequency. You should see the changes on the shape of the
pulses.
6.3.

Carbon-Fiber Electrodes

Most voltammetric measurements in today's biological investigations involve the use of
carbon-fiber electrodes. These electrodes can be purchased or you can make your own. For
use with the VA-10X voltammeter the electrodes must fit to the BNC connector at the input
of the headstage. Two types of connection are commonly used:
1) direct connection via a BNC pin that is soldered onto the end of the electrode or
2) connection via a metal/liquid junction, for example using a 3 M KCl solution to interface
the end of a carbon fiber to a Ag/AgCl wire.
For the first type of connection no special holder is required. For the metal/liquid junction
type a special electrode holder must be used. For some electrodes a patch-pipette holder is
adequate.
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version 7.0
VA-10X User Manual
page 15