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2-6
Functional Description
noise is amplified and digitized. As a result, you must carry out the
measurement of low-level signals carefully to minimize noise effects.
Low-level transducers are best used with signal conditioning. Always use
the ±20mV, 0 to 20mV, ±100mV, and 0 to 100mV ranges with the
differential input mode.
The tables below show throughput for various configurations. Note that
these throughputs are based on driving the input with an ideal voltage
source. The output impedance and drive of the source is far more critical
when making large gain changes between two channels whose inputs are
at opposite extremes of their input ranges, as when a signal near
−
20mV
is measured after a signal at near +5V. You will get better performance
driving adjacent channels at the same gain. The source needs to be able to
drive both the capacitance of the cable and the RC (resistor-capacitor
product of the multiplexer resistance and the output capacitance) of the
multiplexer and board. The multiplexer is typically about 360
Ω
(1k
Ω
maximum) in series with 90pF output capacitance.
The maximum throughput for sampling one channel at one gain (any
gain) is 333 ksamples/s. The throughput for channel-to-channel sampling
with fixed gain in bipolar mode (0.024% maximum error) is as shown in
Table 2-3.
Table 2-3. Throughput for Channel-to-Channel Sampling in Bipolar Mode with
Fixed Gain
DAS-1801HC Range
DAS-1802HC Range
Throughput
—
±10.0V
312.5 ksamples/s
±5.00V
±5.00V
312.5 ksamples/s
—
±2.50V
312.5 ksamples/s
—
±1.25V
312.5 ksamples/s
±1.00V
—
312.5 ksamples/s
±100mV
—
312.5 ksamples/s
±20mV
—
75 ksamples/s
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