User
Guide
for
Axoclamp
900A
Risetime
The
risetime
is
typically
given
as
the
time
taken
for
a
signal
to
increase
from
10%
to
90%
of
its
peak
value.
The
more
heavily
a
step
response
is
filtered,
the
greater
the
10–90%
risetime.
For
the
4
‐
pole
Bessel
filter
in
the
Axoclamp
900A,
the
filtered
10–90%
risetime
(T
r
,
in
ms)
of
a
step
input
depends
on
f
c
(in
kHz)
approximately
as:
T
r
≈
0.35/f
c
(This
can
be
measured
by
applying
Seal
Test
to
the
model
BATH
in
V
‐
Clamp
mode
and
looking
at
“Scaled
Output:
Membrane
Current”
while
changing
the
filter
setting.)
Suppose
you
are
interested
in
measuring
action
potentials,
for
which
you
expect
the
10–90%
risetime
to
be
about
0.4
ms.
You
would
then
choose
the
filter
cutoff
frequency
to
be
high
enough
that
the
filter
risetime
is
about
ten
times
faster
than
0.4
ms
so
the
action
potentials
are
minimally
distorted
by
the
filter.
According
to
the
above
equation,
then,
the
appropriate
filter
setting
would
be
10
kHz.
In
practice,
you
may
need
to
make
other
compromises.
For
example,
if
the
signal
is
very
noisy
you
may
wish
to
filter
more
heavily
and
accept
that
the
action
potential
risetime
is
artifactually
slowed.
Highpass
Filter
The
Scaled
Output
signal
can
be
highpass
filtered
by
setting
the
AC
value
in
the
Output
Gains
and
Filters
section
of
the
main
Axoclamp
900A
Commander
panel.
This
is
typically
done
in
order
to
remove
a
DC
component
of
the
signal.
When
the
filter
cutoff
is
set
to
DC
this
highpass
filter
is
bypassed.
Blanking
A
common
problem
when
using
stimulating
electrodes
is
that
some
of
the
stimulus
is
directly
coupled
into
the
recording
microelectrode.
This
can
saturate
the
coupling
capacitors
of
subsequent
AC
recording
circuits.
The
saturation
effects
may
take
tens
or
hundreds
of
milliseconds
to
subside.
110
