PC-505B Manual, Rev. 201013
Warner
Instruments
A Harvard Apparatus Company
9
any externally applied command voltages connected to the
COMMAND IN
input BNC by factors
of
x0.1
,
x0.01
, and
x0.001
.
Internal or external commands are activated by moving the
COMMAND SENSITIVITY
toggle
into the
on
position. When switched
off
, these modifiers are disconnected
from the
COMMAND
pathway.
Test pulse
When
internal
command
is selected and
COMMAND SENSITIVITY
is switched
on
, a 1V p-p
square wave test pulse (line frequency; 50/60 Hz) is generated by the
PC-505B
. The test
pulse is attenuated by the
SENSITIVITY SELECTOR
toggle and is available for adjustment of
capacitance compensation, measurement of pipet resistance, or for monitoring the formation
of a gigohm seal at the electrode tip.
S
ENSITIVITY SELECTOR
setting
Amplitude of test pulse
square wave (p-p)
x0.1
100 mV
x0.01
10 mV
x0.001
1 mV
When
external command
is selected, the internal
TEST PULSE
circuitry is disabled and
commands appearing at the
COMMAND IN
BNC are attenuated and available to be applied to
the headstage.
Junction Zero and Auto Zero
These controls set the pipette current to zero after the pipette is placed in the test
solution and prior to seal formation. This circuitry is used to compensate for electrode
potentials, liquid junction potentials and other offset voltages, and establishes a zero
baseline reference potential. The 10-turn
JUNCTION ZERO
control manually adjusts I
m
between
120 mV
with immediate response.
With the
AUTO ZERO
toggle switch in the
on
position (auto zero LED
on
) depressing the
associated pushbutton zeros the current automatically. The settling time is rapid when used
with M
pipette resistances, but can take several seconds if used with G
resistances. For
complete compensation, hold the pushbutton in until I
m
on the
METER
reads
zero
.
NOTE:
With
AUTO ZERO
turned
on
, the manual junction control remains active. In this mode,
depressing the auto zero pushbutton will zero any manual setting, holding potential, and
time-averaged test pulse or command voltage present. Switching
AUTO ZERO
off
restores the
uncompensated current and voltages. To re-zero, repeat using either manual or auto zeroing.
