TEC-B-01 User Manual
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version 1.1
page 18
Enable the OSCILLATION SHUTOFF unit from BA-03X with a moderate THRESHOLD
(DISABLED / RESET switch (#
32
)
in middle position, OSCILLATION SHUTOFF LED
green, THRESHOLD potentiometer set to a low value, but not to the most left position)
Set the TEC-B-01 amplifier with the MODE OF OPERATION switch (#
1
) to VC mode.
The BA-03X POTENTIAL display should show the holding potential of –50 mV and the TEC-
B-01 display (I
CEL
) the holding current of –5 µA (according to Ohm's law).
It is very likely that the display shows a holding potential of slightly less than –50 mV because
the controller is in GAIN ONLY mode and the GAIN is low. Increasing GAIN and activating
the INTEGRATION will enhance the control loop and therefore increase accuracy.
Hint
: If the system oscillates as soon as you switch to VC mode switch back to CC mode and check
the settings. GAIN too high? CAPACITY COMPENSATION not 0? THRESHOLD potentiometer of
the OSCILLATION SHUTOFF unit at the most left position? R
S
-COMP. not switched OFF?
Apply a test pulse of 20 mV to the cell model by giving a voltage step of 0.2 V to COMMAND
INPUT (#
15
). The length of the test pulse should be at least 30 ms.
You should see a potential step of 200 mV amplitude at BA-03X POTENTIAL OUTPUT
(#
36
).
Note
: If you expect the POTENTIAL display to show the value of the potential step (in this case +20
mV amplitude, i.e. –30 mV) remember that the display is rather sluggish and may not display the right
value (depending on the length of the step). The same is true for the CURRENT display.
5.6.
Tuning the VC mode
In VC mode there is the problem that the voltage step is often not strictly angular shaped. But, for
instance, increasing the clamp speed by tuning the CAPACITY COMPENSATION of the potential
electrode or increasing GAIN also increases noise. Therefore, the settings of the different parameters
result always in a compromise between the stability, accuracy, noise and control speed. In this chapter
we will give some practical hints, how to optimize the accuracy and speed of the clamp. The
theoretical background of adjustment criteria is discussed in chapter 9 (see also Polder and Swandulla,
2001).
The main considerations are: Do I expect rapid or slow responses to voltage changes? How much noise
can I accept? Is it possible to use electrodes with low resistance?
General
: The speed and accuracy of the voltage clamp control circuit is mainly determined by the
question how much current can be injected and how fast can this happen. Thus, the more current the
system can inject within a short time the better the quality of the clamp (see chapter 9).
