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USB-1616HS-2 User's Guide Functional Details
19
Analog input
The USB-1616HS-2 has a 16-bit, 1-MHz A/D coupled with 16 single-ended, or eight differential analog inputs.
Seven software programmable ranges provide inputs from ±10 V to ±100 mV full scale.
Analog input scanning
The USB-1616HS-2 has several scanning modes to address various applications. You can load the 512-location
scan buffer with any combination of analog input channels. All analog input channels in the scan buffer are
measured sequentially at 1 µs per channel by default.
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 7
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 7. Analog channel scan of voltage inputs example
Example: Analog channel scanning of voltage and temperature inputs
Figure 8
shows a programmed pre-acquisition scan made up of six analog channels (Ch0, Ch1, Ch5, Ch11,
Ch12, Ch13). Each of these analog channels can have a different gain. You can program channels 0 and 1 to
directly measure TCs.
In this mode, oversampling is programmable up to 16384 oversamples per channel in the scan group. When
oversampling is applied, it is applied to all analog channels in the scan group, including temperature and voltage
channels. Digital channels are not oversampled.