HEKA Elektronik EPC 10 USB, Hardware Manual, Page: 28 / 81

22 Verifying and Testing the EPC 10 USB
The peak current can be calculated from
I
max
= C
m
∗
U/τ = 22 pF
∗
5 mV / 112 µs = 982 pA
With the actual gain setting of 20 mV/pA this would generate a voltage of 19.6 V at the current-to-voltage converter
output, which exceeds the amplifier’s voltage range. This is signalized by the red clipping indicator at the amplifier
and in the ”virtual panel” in
Patchmaster
(3).
Activate the C-slow compensation by selecting the 100 pF range from the Range field (4). Now start the com-
pensation by increasing the C-slow (5) and the R-series (6) values either separately or by using the using the drag
button (7) for both parameters (drag the mouse in all four directions). With some exercise you will get a better
feeling for these parameters and how they effect the recording. With increasing quality of the compensation you
should approach the real values of the model circuit and the transients should disappear (black line). Instead of
compensating
C-slow ”by hand” you can also press the Auto button (8) in the C-slow section of the amplifier
control panel for an automatic compensation of C-slow and R-series . If the compensation fails, the E -field in the
Auto button becomes red. When this happens, you should repeat the auto-compensation, until it succeeds and
the E -field becomes normal again.
Note: The speed and success of automatic C-slow compensation depends on the actual values of C-slow
and R-series . These two values should be reasonably near to the real values. Therefore, you should
always check, whether the values are reasonable before executing the automatic compensation. It is
much better to have too large estimates than too small ones.
Figure 4.6: After C-slow compensation
Note: If you are a novice to patch clamping it is useful to perform the C-fast and C-slow compensation
at least a couple of times manually before getting used too much to the convenience of the automatic
routines. Doing so you will get a better feeling for the quality of a recording and how it is affected by
the various parameters, especially the input resistance
R-series .
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