Clamp mode switch
In voltage clamp mode (MODE switch in upper position), all command controls are active
with the exception of the CURRENT HOLD command (in COMMANDS block). The range of voltage
clamp potentials at the headstage input is ± 200 mV.
Zero current mode (MODE switch in center position) is a transition mode between voltage
clamp and current clamp. It disengages all commands and functions from the headstage
with the exception of the ZAP controls.
The primary uses for zero current mode are: 1) to protect the preparation when
switching between voltage and current clamp modes, and 2) to preset the voltage hold or
current hold settings prior to switching to voltage or current clamp modes, respectively.
In current clamp mode (MODE switch in lower position), all commands are again active.
The current range at the preparation is limited by the ± 10 V input maximum and the
headstage resistor, as follows:
• ± 20 nA with the 500 M resistor
• ± 200 nA with the 50 M resistor
NOTE: Current clamp mode does not operate with the PROBE SELECT toggle set to high. The
low headstage resistance is automatically selected when in current clamp mode.
Gain
The GAIN control selects the amplifier gain in units of mV/pA. The gain scale on this
control is modified by the PROBE RESISTOR select toggle (x0.1 or x1.0 for the low setting, and
x10 for the high setting).
LED’s indicate the selected gain scale modifier. The clipping LED lights when the
instrument I
m
output exceeds the amplifier limits.
4-Pole Bessel filter
The I
m
output signal can be filtered using the internal low–pass 4-pole Bessel filter
selectable from 50 Hz to 20 kHz in 9 steps. The full amplifier bandwidth of 25 kHz is available
by selecting bypass with the ACTIVE/BYPASS toggle switch. The filtered I
m
signal is present at
two BNC outputs labeled I
m
located at both the front and rear panels.
Voltammetry
The PC-505B can be used as a potentiostat for voltammetric measurements. A rear panel
POTENTIOSTAT SWITCH increases maximum output of the VOLTAGE HOLD control (in the
COMMANDS block) to ± 1 V and increases the maximum COMMAND IN signal to ± 2 V. The P STAT
LED lights to indicate on status for this switch.
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