National Instruments 6023E - Manual (Page 24)

Chapter 3 Hardware Overview
© National Instruments Corporation 3-5 6023E/6024E/6025E User Manual
Figure 3-3. Dithering
Multichannel Scanning Considerations
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.
a. Dither disabled; no averaging b. Dither disabled; average of 50 acquisitions
c. Dither enabled; no averaging
100 200 300 400 0 500
-4.0
-2.0
0.0
2.0
4.0
-6.0
d. Dither enabled; average of 50 acquisitions
LSBs
LSBs LSBs
LSBs
6.0
100 200 300 400 0 500
-4.0
-2.0
0.0
2.0
4.0
-6.0
6.0
100 200 300 400 0 500
-4.0
-2.0
0.0
2.0
4.0
-6.0
6.0
100 200 300 400 0 500
-4.0
-2.0
0.0
2.0
4.0
-6.0
6.0
a. Dither disabled; no averaging b. Dither disabled; average of 50 acquisitions
c. Dither enabled; no averaging
100 200 300 400 0 500
-4.0
-2.0
0.0
2.0
4.0
-6.0
d. Dither enabled; average of 50 acquisitions
LSBs
LSBs LSBs
LSBs
6.0
100 200 300 400 0 500
-4.0
-2.0
0.0
2.0
4.0
-6.0
6.0
100 200 300 400 0 500
-4.0
-2.0
0.0
2.0
4.0
-6.0
6.0
100 200 300 400 0 500
-4.0
-2.0
0.0
2.0
4.0
-6.0
6.0