Need Help with SCXI 1100 Scan Problem

[*.com]

Using the top level "SCXI Temperature Scan" vi, it becomes obvious
that you cannot skip channels on any one module (i.e. if I want to
scan channels 1-3, then skip 4 and get 5). Seemingly, this would be
done by 1:3 input on array element 0, and then 5 on array element 1.
However, when the same modeule is referenced on 2 consecutive array
locations, the scan fails.

Question 1: Is there any other vi that I can use to skip channels
easily ?

Question 2: Has anyone had success with Open TC detection ? We have
not - which necessitates skipping channels.

Question 3: Why does a bad channel corrupt adjacent channels (or
sometimes the whole card) ? Can it be prevented ?

Hardware: SCXI-1000 w/SCXI-1100, 1122, 1123, AT-MIO-16X


Software: Win95, LabView 5.0.

Thanks in advance and please reply to this group.

Kevin

[Brent B.]

First, the SCXI-1100 cannot be randomly scanned, only contiguous channels may be scanned within a scan string. However, there are SCXI modules that do facitlitate random scanning such as the SCXI-1125, 1530, 1520, ect. There is also one other caveot, only LV is able to do random scanning. One cannot achieve random scanning through the C API.

Second, there are a couple of reasons as to why Open TC detection effects adjacent channels on the SCXI-1100 but also the DAQ card itself. Open TC detection is achieved by placing a pull-up to resistor to 5VDC. When an SCXI channel is configured for a TC (high gain) this 5VDC input saturates and overloads the SCXI amplifier as well as the DAQ amplifier. This effect is especially noticable with the 1100 due to its single filt
er, single amplifier configuration. Since the amplifier is overloaded, it does not have time in many cases to reset before the next channel is scanned. The only method of prevention that I can think of right now is to increase your interchannel delay so that the amp has time to settle from the overload state.

As a side note, the 1102 has 32 seperate amps and filters and in many cases this effect is not noticed. Even better is the 1112 because it has 8 seperate amps and filters but it also has random scanning so that the Open channel can be omitted from the scan string.