Description of the Hardware EPC9 Manual 12
Chassis Gnd: The chassis is connected to the ground line of the power cord, as is
typical of most instruments. The Signal Ground is kept separate from the chassis to
avoid ground loops, but is connected to it through a 10 Ω resistor.
Test Input: This input is used for the Test mode. An external stimulus fed into the
Test Input is converted into a current (scaling is fixed at approximately -100 pA/V)
and injected as a test signal into the probe input. The current injection circuitry has a
very wide bandwidth (1 Hz to 1 MHz), allowing very precise determination of the
frequency response of the current monitor circuitry. With the Gain set to 10 mV/pA,
any signal applied to the Test Input connector will be reproduced with approximately
the same amplitude (but inverted) at the Current Monitor outputs.
Note: You can use the internal stimulator to generate a test pulse for determining the
accuracy of the calibration parameters. Simply connect the “Test Output” (DA 2)
with the “Test Input” and stimulate with the desired voltage pulse.
External Stim. Input: Signals from an external stimulus source are applied here;
they can be summed with the internal stimulus if desired. The combined stimulus
signal is passed through a 2-pole filter to round off stepwise changes in voltage. This
avoids nonlinearities (from slew-limiting amplifiers) in the command processing
circuitry and also reduces the amplitude of the current transients from rapid
charging of the pipette. Two degrees of filtering, specified as the risetimes (time from
10% to 90% of the amplitude of a step change) are available in the software: 2 µs,
which is the minimum required to avoid nonlinearities in the internal circuitry, and
20 µs, which is preferable for all but the fastest measurements, to reduce the
capacitive transients.
Voltage Monitor: This output signal provides a monitor of the pipette potential. It is
scaled up by a factor of 10 relative to the potential applied to the pipette. The output
impedance is 50 Ω. The unscaled signal may be viewed on the software oscilloscope.
Current Monitor: The output signals are filtered according to the settings in the
software. Positive voltages correspond to currents flowing out of the pipette.
Typically, the left-hand output (Filter 1) is fed to a data recorder (e.g., tape recorder,
PCM/VCR combination, or DAT recorder) to record the signal at wide bandwidth,
while the additionally-filtered signal from the right-hand output (Filter 2) is applied
to an oscilloscope for monitoring the progress of the experiment. Either signal may
be viewed on the software oscilloscope.
Probe: This input accepts the multi-pin connector of the head stage.
Signal GND: This banana jack is a high-quality signal ground connection that can be
used to ground other parts of the experimental setup as necessary (see Chapter 8.
Patch-Clamp Setup on page 67).
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