Appendix A
SCXI Troubleshooting and Common Questions
A-3
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My chassis worked fine until I inadvertently removed and reinserted
a module while the chassis was on. Now my chassis does not turn on.
What can I do?
You may have blown a fuse. Consult the SCXI Chassis User Manual for
more information on your fuses.
I am using an SCXI-1100 module and SCXI-1300 terminal block with
a thermocouple that measures room temperature. How do I stop the
thermocouple reading from fluctuating erratically?
Most thermocouples are floating signal sources with low common-mode
voltage; they require a path for bias currents from the SCXI-1100 amplifier
to ground. Check jumper W1 on your SCXI-1100 module to make sure the
jumper is in the factory-default position. Make sure that you have grounded
the negative lead of each floating thermocouple and that your grounded
thermocouples do not have high common-mode voltages. Average your
temperature readings to minimize fluctuations that remain.
I understand my SCXI-1100 has software-programmable gain, but I
need to continuously acquire data at different gains without stopping
to change the gain on my SCXI module. How can I do this?
You can use any MIO device to accomplish this. Assume you need to set
the gain for the first eight channels on the module to 100 and the gain for
the last 24 channels to 1,000.
Set the SCXI module gain to the lowest required gain and create multiple
entries in the MIO device scan list that use different MIO device gains
so that the total gain on each channel will be the desired gain. For this
example, set the SCXI module gain to 100, and set the MIO device gain
to 1 for the first eight channels and 10 for the last 24 channels.
In NI-DAQ for PC compatibles and NI-DAQ for Macintosh, use the
function call
SCXI_Set_Gain
to set the SCXI-1100 gain to 100. Then call
the function
SCXI_MuxCtr_Setup (deviceNumber, 1, 1, 8)
; this
specifies that eight SCXI module channels are scanned for each entry in the
MIO device scan list. The MIO device channel list is
{0, 0, 0, 0}
(remember that in multiplexed mode only MIO device channel 0 is used),
and the MIO device gain list is
{1, 10, 10, 10}
. The first eight channels
on the module will have a total gain of 100 • 1 = 100, and the last
24 channels will have a total gain of 100 • 10 = 1,000. Notice that you are
