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 GΩ measuring resistor). If the signal source is a sine-wave
generator, the frequency response of the patch clamp can be verified directly.
To Next Page
Loading...