Measurement Computing USB-1616HS-BNC User Manual page 16

USB-1616HS-BNC User's Guide Functional Details
For example, in the fastest mode, with ADC settling time set to 1 µs, a single analog channel can be scanned
continuously at 1 MS/s; two analog channels can be scanned at 500 kS/s each; 16 analog input channels can be
scanned at 62.5 kS/s.
Settling time
For most applications, leave the settling time at its default of 1 µs. However, if you are scanning multiple
channels, and one or more channels are connected to a high-impedance source, you may get better results by
increasing the settling time. Remember that increasing the settling time reduces the maximum acquisition rate.
You can set the settling time to 1 µs, 5 µs, 10 µs, or 1 ms.
Example: Analog channel scanning of voltage inputs
Figure 5 shows a simple acquisition. The scan is programmed pre-acquisition and is made up of six analog
channels (Ch0, Ch1, Ch3, Ch4, Ch6, and Ch7). Each of these analog channels can have a different gain. The
acquisition is triggered and the samples stream to the PC. Each analog channel requires one microsecond of
scan time—therefore the scan period can be no shorter than 6 µs for this example. The scan period can be made
much longer than 6 µs—up to 1 s. The maximum scan frequency is one divided by 6 µs, or 166,666 Hz.
Figure 5. Analog channel scan of voltage inputs example
Since the targeted number of oversamples is 256 in this example, each analog channel in the scan group
requires 256 microseconds to return one 16-bit value, making the minimum scan period for this example 7 x
256 µs, or 1792 µs. The maximum scan frequency is the inverse of this number, 558 Hz.
Example: Analog and digital scanning, once per scan mode
The scan is programmed pre-acquisition and is made up of six analog channels (Ch0, Ch2, Ch5, Ch11, Ch13,
Ch15) and four digital channels (16-bits of digital IO, three counter inputs.) Each of the analog channels can
have a different gain.
The acquisition is triggered and the samples stream to the PC via the USB cable. Each analog channel requires
one microsecond of scan time. Therefore, the scan period can be no shorter than 6 µs for this example. All of
the digital channels are sampled at the start of scan and do not require additional scanning bandwidth as long as
there is at least one analog channel in the scan group. The scan period can be made much longer than 6 µs, up to
1 second. The maximum scan frequency is one divided by 6 µs or 166,666 Hz.
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