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Tutorials
MultiClamp 700A Theory and Operation, Copyright 2000, 2001 Axon Instruments, Inc.
A sawtooth pattern appears on Scaled Output (Figure 2.24). Each segment of the
sawtooth is actually an incompletely relaxing exponential.
Figure 2.24
5. Set the Tuning frequency to 50 Hz and note that, on an expanded oscilloscope
timebase, a step is visible at the beginning of each segment of the sawtooth. This
step is due to the resistance of the model “electrode”. As in the case of whole-cell
voltage clamp (Tutorial 4), electrode series resistance can introduce errors to
current-clamp recordings and needs to be compensated electronically. In current-
clamp mode, Rs is compensated using Bridge Balance.
Figure 2.25
Check the Bridge Balance checkbox and, using glider control, vary the M
Ω
value
until the step is eliminated. Alternatively, press the Auto Bridge Balance button
for automatic adjustment. The optimum value is about 10 M
Ω
, which is the
electrode resistance of the model cell.
To the left of Bridge Balance is the Output Zero button. This works exactly like
the corresponding button in voltage clamp, removing constant DC offsets.
