Chapter3 HardwareOverview
©NationalInstruments Corporation 3-5 6023E/6024E/6025EUser Manual
Figure3-3. Dithering
Multichannel Scanning Considerations

Thedevices can scan multiple channels at the same maximu mr atea s their

single-channelrate; however, pay careful at tention to the settling times for

each ofthe devices. No extra settling t ime is necessary between channels

aslong as the gainis constant and source impedances are low. Refer to

Appendix A, Specifications, for a complete listing of settling times for each

ofthe d evices.

When scanning among channels at variousgains, the settling times can

increase.When the PGIA switches to a higher gain, the signal on the

previouschannel 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

channel1 , and suppose the PGIA is programmed to apply a gain of one to

channel0 and a gain of 100 to channel 1. When the multiplexer switches to

channel1 and the PGIA sw itches 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 4000500
-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 4000 500
-4.0
-2.0
0.0
2.0
4.0
-6.0
6.0
100 200 300 4000 500
-4.0
-2.0
0.0
2.0
4.0
-6.0
6.0
100 200 300 4000 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 4000500
-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 4000 500
-4.0
-2.0
0.0
2.0
4.0
-6.0
6.0
100 200 300 4000 500
-4.0
-2.0
0.0
2.0
4.0
-6.0
6.0
100 200 300 4000 500
-4.0
-2.0
0.0
2.0
4.0
-6.0
6.0