Testing the EPC9
EPC9 Manual
34
Measuring the Frequency Response
The
Test
mode allows one to easily check the basic current-measuring circuitry of the
EPC9. Select
Test
from the
Mode
list, connect a function generator or stimulator to
Test Input
, and connect the right-hand
Current Monitor Output
(Filter 2) to an
oscilloscope. Alternatively, you can connect the
Test Output
of the internal
stimulator (DA 2) to the
Test Input
and look at the response. With the
Gain
set to 10
mV/pA, any signal applied to the
Test Input
connector should be reproduced with
the same amplitude at the
Current Monitor Output
. An applied signal amplitude of
about 1 volt is appropriate.
Note:
The probe input usually needs to be shielded from low-frequency noise. A simple
way to do this is to cover the input connector with a cap made from aluminum foil.
Note:
The Test mode current-injection system is intrinsically AC-coupled, which means
that long (>30 ms) pulses may be distorted in shape. Also, large low-frequency
inputs can cause the current-injection circuitry to saturate.
The action of the internal filters on the background noise level and the temporal
response can be observed by changing Filter 1 and Filter 2. An improved signal-to-
noise ratio should be apparent when the
Gain
is increased to 50 mV/pA or greater
(which selects the 50 G
Ω
measuring resistor). If the signal source is a sine-wave
generator, the frequency response of the patch clamp can be verified directly.
