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The
Model 1900 Polarographic Amplifier has been specifically designed
for low noise, precise amperometric measurements. The features
of this research instrument easily permit the use of a wide
range of commercial polarographic oxygen sensors.
The wide response range of the Model 1900 extends all the
way from 100 pA up to 1 uA with 100% overrange on all scales.
On its most sensitive scale, the resolution is 0.1 pA. The
amplifier output is displayed on the front panel digital meter,
and is available from a BNC connector for chart recorders,
polygraphs, A/D converters or other display devices. Accuracy,
ease-of-use, and recording flexibility are design features
for the researcher’s satisfaction. No head stage is
required to achieve the 0.1 pA sensitivity, reducing the congestion
at the electrode measurement site. The input connections are
made conveniently through standard BNC connections. The front
panel scale adjustment does not require zero current readjustment
when there is a change in scale, reducing instrument set-up
time. The digital meter display is switch selectable for mmHg,
percent (x1 or expanded x10), or absolute current. The instrument
gain automatically adjusts for polarity of the polarization
voltage, even for an external polarization input.
The maximum input bias current is less than 1 pA at normal
room temperature. With the 10-turn potentiometer knob, the
Zero Current control can be used to eliminate this input bias
current of the polarographic sensor at 0% oxygen. The Zero
Current can be turned off to determine the absolute current
level. This is a convenient way to check electrode resistance.
The amplifier offers two polarization voltage methods. One
is from the instrument’s internal source set by the
Internal Voltage knob; the other is from an external source
into the Ext In BNC connector. A novel feature for the external
source is that a variety of polarization waveforms may be
used. The display meter can be switched to monitor the polarization
voltage. The voltage can also be monitored via the Monitor
Out BNC connector. An external GATE signal may be used to
switch on or off the polarization voltage applied to the electrode,
for further experimental control.
The Model 1900 has been designed to minimize the effects
of artifacts and noise. While for many applications a single-ended
sensor input may be adequate, differential measurements may
also be made. Built-in low pass and notch filters further
reduce spurious noise. The instrument has features to withstand
the rigors of a research environment, with protection against
normal static or DC overvoltages.
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