FUNCTIONAL CHECKOUT
•
5
Chapter 2
4) Turn the meter switch to I
RMS
. Note the reading on the rms noise display for the three
headstage configurations (toggle the configuration between the PATCH and WHOLE
CELL positions). The expected values under optimal conditions are:
CV 203BU
PATCH β = 1 ≈ .045 pA rms
WHOLE CELL β = 1 ≈ 0.55 pA rms
WHOLE CELL β = 0.1 ≈ 1.60 pA rms
I
RMS
is shown on the panel meter always in a 5 kHz bandwidth using a Butterworth filter
that is independent of the front-panel lowpass Bessel filter. The front-panel gain does
not affect this reading.
If the observed values are more than twice the expected values or if the meter is
blanked due to exceeding its range, then check to see that the foil shield is correctly
grounded and that all controls are in the positions noted in 2 above. Also check on the
screen of the oscilloscope for 60 Hz interference or other noise pickup.
Test the PIPETTE CAPACITANCE COMPENSATION and FILTERS:
5) Set CONFIG. to PATCH. Set the oscilloscope gain to 0.5 V/div, trigger to line, and the
sweep speed to 2 ms/div. Connect the oscilloscope to the Scaled Output with a BNC
cable. Turn on the SEAL TEST switch. You should see oppositely going capacitance
transients at about 8 ms intervals (about 10 ms for 50 Hz line frequency). Turn the
FAST MAG and FAST τ controls and verify that the capacitance transients change
their size and amplitude. Do the same with the SLOW MAG and SLOW τ controls.
The change is subtle. You may need to change settings on the oscilloscope to see an
effect. Switch from PATCH to WHOLE CELL (β = 1) and repeat the above
procedures. Switch between the 1, 2, 5, 10, and 100 kHz positions on the LOWPASS
BESSEL FILTER control and verify that the capacitance transient signals seen on the
oscilloscope screen are affected.
Turn off SEAL TEST.
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