Multichannel Scanning Considerations; Figure 3-3. Dithering - National Instruments 6023E User Manual

LSBs LSBs
6.0 6.0
4.0 4.0
2.0 2.0
0.0 0.0
-2.0 -2.0
-4.0 -4.0
-6.0 -6.0
0 0 100 100
a. Dither disabled; no averaging a. Dither disabled; no averaging
LSBs LSBs
6.0 6.0
4.0 4.0
2.0 2.0
0.0 0.0
-2.0 -2.0
-4.0 -4.0
-6.0 -6.0
0 0 100 100
c. Dither enabled; no averaging c. Dither enabled; no averaging

Multichannel Scanning Considerations

© National Instruments Corporation
200 200 300 300 400 400 500 500
200 200 300 300 400 400 500 500
The devices can scan multiple channels at the same maximum rate as their
single-channel rate; however, pay careful attention to the settling times for
each of the devices. No extra settling time is necessary between channels
as long as the gain is constant and source impedances are low. Refer to
Appendix A, Specifications, for a complete listing of settling times for each
of the devices.
When scanning among channels at various gains, the settling times can
increase. When the PGIA switches to a higher gain, the signal on the
previous channel can be well outside the new, smaller range. For instance,
suppose a 4 V signal connects to channel 0 and a 1 mV signal connects to
channel 1, and suppose the PGIA is programmed to apply a gain of one to
channel 0 and a gain of 100 to channel 1. When the multiplexer switches to
channel 1 and the PGIA switches to a gain of 100, the new full-scale range
is ±50 mV.
LSBs LSBs
6.0 6.0
4.0 4.0
2.0 2.0
0.0 0.0
-2.0 -2.0
-4.0 -4.0
-6.0 -6.0
0 0 100 100
b. Dither disabled; average of 50 acquisitions b. Dither disabled; average of 50 acquisitions
LSBs LSBs
6.0 6.0
4.0 4.0
2.0 2.0
0.0 0.0
-2.0 -2.0
-4.0 -4.0
-6.0 -6.0
0 0 100 100
d. Dither enabled; average of 50 acquisitions d. Dither enabled; average of 50 acquisitions

Figure 3-3. Dithering

3-5
Chapter 3 Hardware Overview
200 200 300 300 400 400 500 500
200 200 300 300 400 400 500 500
6023E/6024E/6025E User Manual