Measurement Computing USB-1616HS-BNC, User Manual

Page: 18 / 49

USB-1616HS-BNC User's Guide Functional Details
18
If the three counter channels are all returning 32-bit values and the digital input channel is returning a 1-bit
value, then 18 samples are returned to the PC every scan period, with each sample being 16-bits. Each 32-bit
counter channel is divided into two 16-bit samples—one for the low word and the other for the high word. If the
maximum scan frequency is 166,666 Hz, then the data bandwidth streaming into the PC is 3 MS/s. Some slower
PCs may have a problem with data bandwidths greater than 6 MS/s.
The USB-1616HS-BNC has an onboard 1 MS buffer for acquired data.
Averaging
Certain acquisition programs apply averaging after several samples have been collected. Depending on the
nature of the noise, averaging can reduce noise by the square root of the number of averaged samples.
Although averaging can be effective, it suffers from several drawbacks:
 Noise in measurements only decreases as the square root of the number of measurements—reducing RMS
noise significantly may require many samples. Thus, averaging is suited to low-speed applications that can
provide many samples.

Only random noise is reduced or eliminated by averaging. Averaging does not reduce or eliminate periodic
signals.
Analog output
The USB-1616HS-BNC has two 16-bit, 1 MHz analog output channels. Analog outputs can be updated at a
maximum rate of 1 MHz.
The channels have an output range of -10 V to +10 V. Each D/A can continuously output a waveform. In
addition, a program can asynchronously output a value to any of the D/A channels for non-waveform
applications, assuming that the D/A is not already being used in the waveform output mode.
When used to generate waveforms, you can clock the D/As in several different modes.

Internal output scan clock
: The onboard programmable clock can generate updates ranging from 1 Hz to
1 MHz.

External input scan clock
: A user-supplied external input scan clock at XPCR can pace both the D/A and
the analog input.

Internal input scan clock
: The internal ADC scan clock.
Example: Analog channel scanning of voltage inputs and streaming analog
outputs
The example shown in Figure 8 adds two DACs and a 16-bit digital pattern output to the example presented in
Figure 5 on page 16.