LabVIEW
How to remove random delay in measurement
Solved!
Hi guys:)
I got a small problem with some measurement I do in a sub-vi. Take a look at the picture (please don't laugh:) )
Some explanation first:
I have to set a digital line High in order to initialize a piece of hardware.
Then I activate two Relays. This is time zero (T0).
Then I have to activate the piece of hardware I initialized at start.
Meanwhile this is activated I have to do the measurement (here called Måling). The measurement is 40 channels. I do measurement on 10 circuits. Each with 3 voltages and 1 current measurement. The voltages are RSE and the current is differential. The sampling is 1000 samples at 1kHz which gives me a resolution of 1 sample every ms.
After the measurement I turn off the relays and the piece of hardware I initialized at start.
The collected data is transformed into an array of 40 rows and 1000 columns with data. In my for-loop I extract the data and do some comparison and put the data into a graph.
Now comes my problem:
I get a random delay on every measurement. I have used OpenG to get the tickcount (could have used frame structure). In the x-y indicator I get from 1060 - 1072-ish milliseconds. I have tried to subtract the 1000 ms of measurement and added the 60-72-ish millisecond delay to my graph and dataindicators, but it don't work. When I use oscilloscope on the 10 circuits I get the same measurement every time. When I do it in Labview it becomes worng because of the delay. I have to get exactly the same measurement as the oscilloscope.
For my own defense:
I have used the DAQ assist because it gives me the hardware wireing diagram on my NI USB-6225 M series. Also I'm not yet familiar with setting up the DAQ without the assist. Yes, I have looked at the forum and the examplefinder, but I spend too much time on it compared to the DAQ Assist.
My measurement should start right after the Relays have been activate. I believe maybe using Triggering on a internal clock, but not quite sure if it will help on the delay. My thoughts of setting this up would be not using the DAQ Assist. Setting up the channels using a For-loop and to do the measurement.
Maybe you can share some thoughts around the delay problematic and maybe give me a clue on where to begin to remove this delay. My DAQ should be ok since it has a limit of 250k samples /sec and I only use 40k samples. Do you think the delay I measure is before or after the 1000 ms measurement?
Regards,
Even
My first reaction is that you're activating the fuses in parallell with your measurement and measure time on both. Move your starting clock to after Fuze setter PÅ and only measure Måling time for starters.
(RelePWR->Fuze PÅ-> time ->Måling->time)
/Y
(welcome neighbouring country) 😉
Hi neighbor:) May I ask, Sweden? Or Finland? Or Denmark?
Well since RelePWR is time zero, and I use all my calculations based on that, and that my hardware Fuze requires to be activated after RelePWR, I thought I had to put the time measurement as I did. I've not yet tried to set the time measurement as you suggested, but I'll post if it helps. Things always looks a bit clearer the day after so I belive you suggestion should work fine:)
I've also made a new coupling and I now wait for the RelePWR to go high. My measurement waits for this trigger before it starts collecting data. Something that in my mind should remove any random delay before the measurement since I force it to start on a trigger event. This I also have to try out today.
Regards,
Even
Hi Even,
Sweden here. You think clearer on the day after? I'm usually hung over. 😄
Keep us updated how it works out.
/Y
Hehe Well the day after Saturdays is an exception!
I used a trigger event and now I get a stable measurement with some +/- 2-3 ms within the relays ( I'll replace them). I put the RelayPWR to trigger the measurement and voilá!
Also your time suggestion worked 😄
New changes:
Regards,
Even
