E9Screen Software EPC9 Manual 44
to make the time constant R-series * C-slow greater than 5 µs to prevent oscillations.
The C-slow value may be adjusted manually by dragging the mouse, or typing, or
automatically by selecting the Auto function. Auto-compensation will adjust C-slow
as well as R-series.
R-series: Adjusts the resistance in series with the slow capacitance (range: 0.1 MΩ -
10 GΩ) to determine the time constant of the C-slow transient and also for R
s
-
compensation. Adjustment is limited by the capacitance values and the range as
described above. The value can be changed manually by dragging the mouse, or
typing, or automatically by clicking on Auto.
<>: This will select both C-slow and R-series. Values for each are changed depending
on whether the mouse is moved horizontally or vertically.
Auto C-slow: Selecting this function performs an automatic compensation of C-slow
and R-series. These settings are used by the Rs-compensation circuitry as the measure
of series resistance. The procedure uses a routine that applies short trains of square-
wave pulses (number and amplitude of these pulses are specified by C-slow Num.
Cycles and C-slow Peak Amplitude), averages the resulting currents and fits an
exponential to deduce the compensation values required to cancel the current (see
Chapter 7. Compensation Procedures on page 59). During this procedure some
parameters are changed temporarily: Rs-comp is turned off, the stimulation is
interrupted and the gain is internally set to an appropriate value (0.2, 2 or 50
mV/pA, depending on the effective gain range). If the C-slow Range is set to Off, it
will automatically be set to the highest possible range, i.e., the 1000 pF range in the
low and medium gain ranges, and the 100 pF range in the high gain range.
Auto-compensation works best when C-fast is canceled beforehand in the cell-
attached configuration. The compensation may be improved by alternating cycles of
Auto C-fast and Auto C-slow. If the compensation fails, the small box in the Auto button
(E) will be darkened to indicate the error. Continuous Auto-compensation can be
performed by selecting Cap. Track option, see below.
Note: It is necessary that reasonable estimates for C-slow and R-series are supplied before
the Auto C-slow is started, otherwise the auto-compensation may fail.
Cap. Track: Selecting this button will perform repetitive Auto C-slow compensation.
Clicking on Cap. Track again will turn it off.
Note: The “Output Cap. Track” option in the EPC9 menu determines whether the
capacitance and G-series values are output as voltages on the DA channels 0 and 1.
If selected, the C-slow value is available at DAC 0, and the G-series value (1/R-
series) is available at DAC 1. The scaling for G-series is 100 nS/V; scalings for C-
slow are 0.5, 5 or 50 pF/V for 30, 100 and 1000 pF ranges, respectively. The DAC
values will be reset to zero when activating “Reset”. Make sure that the trigger DAC
is neither DAC 0 nor DAC 1 when you want to activate "Output Cap. Track".
To Next Page