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Analog Input Features
2-9
Maximum Achievable Throughput Rates
Because you can change input ranges on a per-channel basis, throughput
is likely to drop if you group channels with varying gains in sequence.
The drop occurs because the channels with low-level inputs (magnitude
of 100mV or less) are slower than those with high-level inputs and
because the channels with low-level inputs must drive out the residual
signals left by the high-level inputs. The best way to maximize
throughput is to use a combination of sensible channel grouping and
external signal conditioning. When using the channel-gain queue,
consider the following suggestions.
●
Keep all channels configured for a particular range together, even if
you have to arrange the channels out of sequence.
●
If your application requires high-speed scanning of low-level signals,
use external signal conditioning to amplify the signal to ±5V or 0 to
5V. This method offers the advantages of increasing total system
throughput and reducing noise.
●
If you are not using all the channels, you can make a particular
channel-gain entry twice to allow for settling time. Consequently, you
will ignore the results of the first entry.
●
If you are measuring steady-state signals, do not use the channel-gain
queue. Instead, use software to step through the channels and perform
single-channel acquisitions. For example, using software-controlled
single-channel acquisitions to acquire 1000 samples on channel 0 at a
gain of 1 and then 2000 samples on channel 1 at a gain of 250
virtually eliminates interference. This method is best for measuring
steady-state signals even if all the channels are at the same gain.
Table 2-2. DAS-1802ST/HR Input Gains and Ranges
for Unipolar and Bipolar Modes
Gain
Unipolar Range
Bipolar Range
1
0.0 to +10.0V
−
10 to +10V
2
0.0 to +5.0V
−
5.0 to +5.0V
4
0 to 2.5V
−
2.5 to + 2.5V
8
0 to 1.25V
−
1.25 to +1.25V
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