User
Guide
for
Axoclamp
900A
Bridge
Balance
is
available
only
in
I
‐
Clamp
mode,
when
Membrane
Potential
is
selected
as
the
Scaled
Output
signal.
For
the
Bridge
Balance
algorithm
to
work
correctly,
always
use
Pipette
Capacitance
Neutralization
first.
How
to
use
Bridge
Balance:
Manual
:
Enter
an
estimate
of
the
electrode
resistance
in
the
adjustable
field,
and
then
check
the
checkbox
to
activate
the
circuit.
If
typing
in
the
value,
express
it
in
M
Ω
.
Once
Bridge
Balance
has
been
applied
you
can,
if
necessary,
adjust
the
value
of
the
estimated
resistance
to
tune
the
response.
Auto:
Click
the
Auto
button
to
automatically
apply
compensation.
Bridge
Balance
generates
a
test
pulse
to
calculate
electrode
resistance
and
applies
compensation
accordingly.
It
automatically
sets
the
adjustable
field
to
the
resistance
it
is
compensating
for,
and
checks
the
checkbox.
Auto
can
be
used
whether
or
not
Bridge
Balance
has
already
been
activated.
You
can
fine
‐
tune
the
resistance
value
manually
after
Auto
has
been
applied.
Bridge
Balance
Overview
In
some
experiments
it
may
be
desired
to
inject
a
current
(I)
into
a
cell
in
current
‐
clamp
mode,
e.g.,
to
depolarize
the
cell
and
evoke
action
potentials.
The
flow
of
I
through
the
microelectrode
produces
a
voltage
drop
across
the
electrode
that
depends
on
the
product
of
I
and
the
microelectrode
resistance
(R
e
).
This
unwanted
IR
e
voltage
drop
adds
to
the
recorded
potential.
The
Bridge
Balance
control
can
be
used
to
balance
out
this
voltage
drop
so
that
only
the
membrane
potential
is
recorded.
The
term
“Bridge”
refers
to
the
original
Wheatstone
Bridge
circuit
used
to
balance
the
IR
voltage
drop
and
is
retained
by
tradition,
even
though
operational
amplifiers
have
replaced
the
original
circuitry.
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