User
Guide
for
Axoclamp
900A
The
reader
is
referred
to
the
section
on
Headstages
in
this
chapter
for
specific
recommendations
regarding
the
selection
of
headstages.
Selection
of
the
Current
Recording
Method
There
are
two
techniques
available
for
recording
current.
For
almost
all
applications
the
built
‐
in
current
monitor
gives
excellent
performance,
however
some
users
may
wish
to
bypass
the
current
sensing
resistor
and,
therefore,
have
to
measure
current
using
the
virtual
ground
technique.
The
two
techniques
are
discussed
in
turn
below.
If
you
are
interested
in
obtaining
accurate
subtraction
of
the
linear
capacitive
currents
at
the
make
and
break
of
a
voltage
step,
then
you
must
ensure
that
the
current
measuring
device
has
enough
compliance
to
fully
resolve
these
large
transients.
Table
4
summarizes
the
current
passing
capability
of
the
HS
‐
9A
headstages.
Headstage
R
0
(M
Ω
)
Short-Circuit Current
Conversion
HS-9A ×0.1
100
±1.8 µA
100 mV/nA
HS-9A ×1
10
±18 µA
10 mV/nA
HS-9A ×10
1
±180 µA
1 mV/nA
Table
4.
Current
passing
capacities
in
TEVC
mode.
Series
Current
Measurement
(Internal)
To
monitor
the
clamp
current
it
is
recommended
that
you
use
the
internal
current
monitor
in
the
current
‐
passing
headstage.
Advantages
are
simplicity
and
the
fact
that
only
the
clamp
current
is
recorded,
and
not
other
currents
injected
into
the
chamber
from
iontophoretic
electrodes,
for
example.
Disadvantages
are
that
the
current
measuring
circuit
has
slightly
more
high
frequency
noise
and
also
loads
the
output
of
the
voltage
clamp.
In
some
circumstances
this
extra
load
can
affect
performance.
For
example,
the
×1
headstage
has
a
10
M
Ω
resistance
in
series
with
the
output,
and
the
clamp
102
