Data Logger Timing and Event Recording Issue

Hello all,

I’ve only been using LabView for a week or two, so I’m pretty green and everything that I’ve done so far is by learning from my mistakes, however I have a few issues that are eluding me so I thought I’d post here to get some help. I think my lack of knowledge is the main stumbling block, so please go gently! I have a basic program up and running that is attached.

Here’s some background:

I have a requirement to test the output of four electronic devices during a test. A lack of output from the device indicates that the device under test has failed and the elapsed time from when the test started should be recorded. The output from the devices is a +3.3V logic signal (DC level). The test will be extended in the future to incorporate more channels, but for now four will be use to keep things simple (and utilise existing hardware).  The test system will run for approximately 3000 hrs (~125 days) continuously (so any timer roll-over etc should be accounted for). Due to the nature and length of the test, the timing resolution of the system can be to the nearest second.

LabView Requirements:

-          Monitor four analogue channels (+3.3V DC)

-          Detect when signal falls below a prescribed threshold (say +2.5V DC, but make the level selectable)

-          Plot all four waveforms

-          Indicate a ‘faulty’ channel using a Boolean indicator

-          Display elapsed time (since test starts or since VI first run). One Sec resolution.

-          Log to file the elapsed time when a channel falls below the selected threshold. TDMS or Excel file output.

Equipment:

-          cDAQ-9178 Compact DAQ backplane

-          NI-9229 Analogue card

Issues:

The first issue is with the timing of the program. I’m not sure how to implement this correctly. I could use the Tic command, but I’m not sure how to display the data. I’ve tried using other methods but the time always starts from Friday, 12:00, 1^st Jan 1904. I’m guessing that this is an epoc/reference start time and anything time derived from this should be accounted for?

Second issue is with the logging of data. I’m not sure how to add in a condition that says ‘If threshold <2.5 then log to file data and time etc’ for each analogue channel. Maybe a switch statement is required to test for this condition? Still not entirely sure how to setup the TDMS logging in order to do this? At the moment I'm getting all of the data, when I only want and event occuring on each channel.

Any help would be hugely appreciated!