18
PROBE
An ultra low noise experimental setup and the absence
of capacitive loading effects are made possible by the
use of a probe head stage containing the first
preamplifier gain block and also all circuitry needed for
the other microelectrode terminations.
Capacitive neutralization is at your fingertips with a high resolution
neutralization control located on the probe. This feature gives you
the capability to fine tune signal risetimes when your
microelectrode’s resistances are greater than a few megohms.
A low noise shielded probe cable is so flexible that the lightweight
probe head stage will always stay where you want it. The ten foot
cable and rugged chassis connector make for fast and simple
connection to your experimental setup. A slide-on miniature co-axial
input connector mates with a wide variety of female connectors
made by several manufacturers. Two different mating connectors are
supplied with the 2400 initially. A removable three inch long rod
allows the probe to be mounted directly in your micromanipulator. A
flat removable probe mounting plate is furnished for setups that
necessitate permanent mounting of the probe to a variety of
surfaces and equipment.
a) CAPACITIVE NEUTRALIZATION CONTROL
The neutralization control is a 15 turn trimpot located at the
mounting rod end of the probe. It controls the amount of positive
feedback supplied to the input of the first gain stage of the
preamplifier. It effectively neutralizes up to 100pF of stray input or
microelectrode capacitance by correcting for the degradation in
signal risetime caused by these capacitances in conjunction with the
microelectrode resistance. The algebraic product of the micro-
electrode resistance and the stray capacitance is equal to one "time
constant" or about the length of time in seconds it will take the
signal's leading edge to rise to 63% of its total amplitude. Thus
decreasing this capacitance by neutralization (canceling it with the
