Hi, I am receiving error code 200429 ("Error -200429 occurred at DAQmx
Write; Value passed to the Task/Channels In control is an empty
string") when attempting to run two similar VI's (both of which use two
analog out tasks) seqentially as subVI's. Each one works fine
when run separately, and I only get the error message when they are
both run as subVI's in a single master VI. I can tell this has
something to do with correctly creating/clearing/passing device
channels and have read the 3 or 4 other threads on this error code, but
I still can't seem to figure out how to fix my problem.
I am using Labview with a basic multifuncton DAQ and a separate TTL
counter card (Ortec MCS card) to raster a piezoelectric scanner
while counting photons from a sample. I'm using the tics from the
TTL counter card's onboard clock to synchronize everything.
Attached are 3 files which are minimal representations of my VI's which
are still sufficient to create the error code. The actual VI's I
am using include a timer/counter source (the Ortec MCS card) access via
ActiveX controls, but the timing, counting and ActiveX elements are not
associated with the problem so I have removed those parts for clarity.
In place of the MCS timer I have substituted the 20MHz timebase
on the NI DAQ board.
full_scan_hardwaretimed.vi is the initial scanner VI.
It takes use input for the range, # pixels and dwell time and sends two
AO voltages to an external scanner for rastering the sample
(typewriter-style). The rastering is accomplished using two timed
loops which are synchronized and timed using the output tics from the
Ortec MCS card.
ROI_scan_hardwaretimed.vi is very similar to the initial scanner
VI. It takes 3 additional inputs (x-offset, y-offset, and a
scaling factor <1) and performs another raster scan of the region of
interest ('ROI'). This is where I get the error.
scope_controller.vi is the master VI which runs both Sub VI's
sequentially. They have to be sequential because in between the
full scan and the ROI scan a matlab script processes the full image
determines the offset for the ROI VI. In my actuall full program
the Matlab script actually returns an array of points, and the
ROI_scan_hardwaretimed.vi will need to run multiple times in a
while-loop.
Oddly, I have previously had no troubles with a very similar VI which
collects a full-scale image, processes it in a Matlab script, and then
passes the returned array to a second VI for point-dwelling (as opposed
to smaller ROI image collection). This previous program had no
trouble using the 2 AO's on the DAQ in both sub-VI's. I only
began to encounter the error when I asked it to scan a smaller region
at each point, instead of just sitting stationary at each point.
