NPI SEC-05LX, Operating Instructions Manual

Page: 51 / 69

Tuning Capacity Compensation
Version 1.11 page 3
Figure 2: Errors resulting from wrong compensation of the electrode capacity.
Original data kindly provided by Ajay Kapur. For details see (7).
Tuning Procedure
(see also chapter “Getting Started”, pages 14, 15):
First part: basic setting
In SEC systems the capacity compensation of the electrode is split into two controls, the
coarse control in the headstage and a the fine control at the front panel of the amplifier. The
aim of the first part of the tuning procedure is to set the coarse capacity compensation at the
headstage, so that an optimal, wide range of CAP.COMP. at the amplifier is achieved.
 Insert the electrode into the electrode holder and connect it to the amplifier.

Immerse the electrode, as deep as it will be during the experiment, into the bath solution.

Set the CAP.COMP. control at the amplifier (potentiometer # 24 at the front panel) to a
value around 2 and turn COARSE CAPACITY COMPENSATION at the headstage to the
leftmost position. Select a DUTY CYCLE as desired (#
24 at the front panel).
 Connect the BNC connector ELECTRODE POTENTIAL OUTPUT at the rear panel to an
oscilloscope and trigger with the signal at BNC connector SWITCHING FREQUENCY
(also at the rear panel). The oscilloscope should be in external trigger mode. The time
base of the oscilloscope should be in the range of 250 µs.
 Set the amplifier in CC mode and select the lowest switching frequency (1 to 2 kHz)

Apply positive or negative current to the electrode using the HOLDING CURRENT
control (potentiometer #
21 at the front panel).
 You should see a signal at the oscilloscope similar to those in Figure 3. Turn the
COARSE CAPACITY COMPENSATION carefully clockwise until the signal becomes
as square as possible (lower diagram in Figure 3).
Important : If you use a model cell (e.g. to train yourself in adjusting the capacity
compensation) the capacity of the model cell is always present. Thus, you will get an
approximately square shaped signal with a slight slope as shown in Figure 4 (lower panel).
 Increase the switching frequency to at least 15 kHz. The amplitude and shape of the signal
should not change considerably.