Molecular Devices Axoclamp 900A, User Manual

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User Guide for Axoclamp 900A
the circuitry. It also provides the means for injecting current into the
microelectrode and for neutralizing the input capacitance.
Current in each microelectrode is continuously measured during both
voltage clamp and current clamp. This measurement does not include
currents from sources other than the microelectrode (
e
.g., hum,
iontophoresis, the other microelectrode) and indicates zero if the
microelectrode blocks.
The Meaning of H
A precision resistor (R
0
) inside the headstage sets the headstage current
gain (H). The particular value of H used affects the Bridge range, the
sensitivity to current commands, the sensitivity of the current monitors and
the gain in SEVC mode. Since the effects always appear in multiples of ten,
they are easy to calculate. For your convenience, Table 1 summarizes these
effects. Note that voltage commands during voltage clamp and recorded
voltages are not affected by the headstage current gain value.
H ×10 ×1 ×0.1
R
0
1 M
Ω
10 M
Ω
100 M
Ω
Max. Bridge Balance 8 M
Ω
80 M
Ω
800 M
Ω
Max. Step Command ±10,000 nA ±1000 nA ±100 nA
Max. DC Current
Command
±1000 nA ±100 nA ±10 nA
Ext. Command 100 nA/V 10 nA/V 1 nA/V
Max Total Current
1
12 µA 1.2 µA 0.12 µA
I Output 1 mV/nA 10 mV/nA 100 mV/nA
Max. Gain in dSEVC 3000 nA/mV 300 nA/mV 30 nA/mV
Max. Gain in TEVC 50000 50000 50000
Table 1. How H affects control and measurement range.
1
Assumes that electrode resistance is negligible.
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