Two
identical battery operated current generators are
available. In ordinary use, the two current generators are
operated in parallel providing two distinct currents; one
for preventing substances in the micropipette from outward
diffusion (the retain or hold current) and the second for
actively ejecting charged material. For pipettes with
submicron tips, a hold current may not be necessary if
there is little outward diffusion of pipette material.
Model 260 is powered by two 9-volt alkaline batteries per
side (four, in total); unique circuitry converts the ±9 V
to ±100 V without a transformer, yielding an exceedingly
quiet output.
Single
Channel Operation
Model
260 contains two completely independent, battery operated
current generators which may be operated independently or
in parallel connection. The user need only connect his
external electrode pair to the red and black output
terminals of channel 1 (HOLD) or 2 (EJECT). For currents
below 100 nanoamperes the 100 nanoampere range is
recommended because one may adjust these low current
values with better resolution in the lower current range.
Two
Channel Operation, Hold-Eject
The
electrophoretic release of charged substances from
micropipettes often requires a second current to counter
outward diffusion of material from the delivery pipette.
This current has been referred to in the literature as
"backing, holding or retaining" current.
Operation causes a small current to flow in a direction
that will offset the spontaneous leakage of the active
agent from the pipette until it is required.
AUTO
Operation
The
timing of current flow from each channel of the model 260
can be externally controlled by a pulse generator or
computer that can supply a logic level of at least +5
volts to the AUTO INPUT terminal. Upon application of the
+5 volt command potential to the AUTO INPUT terminal, the
preset current will flow from the output terminals for as
long as the command potential is maintained. Note: If the
instrument is in the MANUAL mode, the application of the
AUTO INPUT signal will halt the current for as long as
this command is maintained. This is the complement of
normal AUTO operation.
Compliance
Alarms
Each
current generator channel contains an audible and visual
alarm circuit that warns when the current amplitude is
large enough to exceed the compliance voltage; in other
words, the load resistance is too high for the amount of
current flowing. The user is thus informed that the
instrument cannot deliver the amount of current indicated
on the panel ammeter. The alarm will also be triggered if
the output path is open-circuited by a loose connection,
air bubble or a blocked micropipette. The initial
compliance voltage exceeds 100 volts but will decrease
proportionately as the battery voltage falls with age.
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français
+49
(0)30 6188845
+45 (0)36 988 355
260
Dual Microiontophoresis Current Generator
