Testing the EPC9
EPC9 Manual
24
C-fast – using the model circuit it is not very critical to misadjust -fast. Continue
adjusting C-fast and -fast unless you see an almost flat line in the oscilloscope (red
line). This should be the case at a around 6 pF (2).
Instead of compensating C-fast ”by hand” you can also press the
Auto
button (4) in
the
CFast
section of the amplifier control panel for an automatic compensation of C-
fast and -fast. If the compensation fails, the
E-
field (5) in the
Auto
button becomes
black. If this happens, you should repeat the auto-compensation, until it succeeds
and the
E-
field becomes normal again. The steps listed above can be automatically
executed by clicking on the
ON-CELL
button or pressing the
‘2’
key on the numerical
keypad. This will execute the following predefined macro that increases the gain and
then performs twice an auto-compensation – considering a possible failure in the
first attempt.
2 : ON-CELL
E Gain: 14 ; set gain to 50 mV/pA
E AutoCFast: ; automatic C-fast compensation
E AutoCFast: ; repeat compensation
E SoundOn: TRUE ; beep
E SoundOn: FALSE ;
Step 3: ”Whole-Cell” Voltage-Clamp Recording
After compensating C-fast well you can now switch into the “0.5 GOhm” position of
the model circuit. This will simulate a “model cell” with 22 pF ”membrane
capacitance”, 500 M
Ω
“membrane resistance” and 5.1 M
Ω
“input resistance” in the
whole-cell configuration. This mode can be used to verify the C-slow controls, the
action of series resistance compensation with C-slow enabled, and the current clamp
mode (see below).
After reducing the gain to 20 mV/pA (1), the
Rmem
field should reflect the changed
“membrane” resistance and display a value close to 500 M
Ω
(2). You should see in
the oscilloscope two capacitive transients (blue line) caused by the 22 pF capacitor in
the model circuit. The “slower” time constant of the model cell – compared to the
“fast” time constant from the middle position – is
τ
= R
s
⋅
C
m
= 5.1 M
Ω
⋅
22pF = 112
µ
s. The peak current can be calculated from I
max
= C
m
⋅
U / = 22 pF
⋅
5 mV / 112
µ
s
= 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 E9SCREEN (3).
Activate the C-slow compensation by selecting the 100-pF range from the
Range
field
(4). Now start the compensation by increasing the
CSlow
(5) and the
RSeries
(6)
