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Control Description
The OC-725C is comprised of three functional channels: A high impedance voltage
sensing channel with capacity compensation and input offset to measure membrane
potential, a current sensing channel with bath clamp to clamp the bath and measure the
membrane current, and a high voltage amplifier to deliver the clamping current.
The complete voltage clamp system consists of the OC-725C, the voltage recording
probe with electrode holder, the current sensing bath probe with silver wire electrodes,
and the current cable with electrode holder.
Front Panel
The instrument front panel is divided into six control blocks titled voltage electrode
[V
], bath electrodes [I
m
rear panel has BNC connectors for gain telegraph output and V
on/off switch, and binding posts for circuit and chassis ground.
Voltage Electrode
The voltage electrode control block contains the voltage probe connector, the
voltage meter, the V
the V
output bnc. Controls for negative
m
capacity compensation are also located in
this block.
The voltage meter reports the membrane
voltage (V
) with a full scale range of
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±199.9 mV.
The voltage probe connector is a 7-pin
DIN connector for attachment of the
voltage probe to the instrument.
The V
offset control is a 10-turn
m
potentiometer providing up to ±200 mV at
the voltage probe input for offset of membrane junction potentials.
The V
electrode test control is used to determine the internal resistance of the voltage
m
probe. When the pushbutton is depressed, a constant 10 nA current is passed through
the voltage electrode producing a voltage drop of 10 mV/MΩ of probe resistance. The
measured potential is displayed by the meter or reported at the V
(at 100 mV/MΩ).
The V
buzz push button facilitates penetration of the voltage electrode by producing a
m
1 kHz square wave at the pipette tip.
The V
x10 output BNC reports the membrane voltage in mV multiplied by 10.
m
negative capacity compensation (-C) has been added to the OC-725C allowing for its
use as an electrometer in intracellular measurements. Input capacitance up to 45 pF can
be neutralized using the two associated controls. A lit LED indicates the active status of
this circuit.
], clamp, commands, and current electrode. The instrument
m
offset control, the electrode test and buzz pushbuttons, and
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x10 output, an alarm
e
x10 output BNC
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9
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