112 • Reference Section
MultiClamp 700A Theory and Operation, Copyright 2000, 2001 Axon Instruments, Inc.
Overload
• OVERLOAD LED on the front panel of the MultiClamp 700A warns when the
signal presented at SCALED OUTPUT or SCOPE saturates (i.e. exceeds ±10.5 V
longer than 10 µs) at any point in the internal circuitry of the amplifier.
• See also Capacitance Compensation, Feedback Resistor.
Inadvertent overloading of the internal circuitry of the MultiClamp 700A is a problem
because it may cause distortion of the signal of interest. The OVERLOAD LED helps
to avoid this problem in two ways.
• By reporting saturation in internal circuits. The SCALED OUTPUT might not
appear to be saturated because it may be heavily filtered, reducing the size of any
saturating transients at the output. OVERLOAD reports any saturation that occurs
before the signal is conditioned.
• By expanding transients. Very fast saturating spikes (e.g. uncompensated
capacitance transients) may be missed under visual inspection on an oscilloscope,
because they are too fast to be seen clearly. The overload sensing circuitry in the
MultiClamp 700A catches any signals that exceed saturation for longer than 10 µs
and illuminates the OVERLOAD LED for at least 500 ms.
If saturation occurs, first try reducing the Output Gain. If the problem persists,
indicating that saturation occurs in the headstage, reduce the Feedback Resistor.
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