Arrive time of start trigger

Dear all NI high speed digitizer experts:
I am asking how can I read the timestamp of the start trigger? In my measurement I configure my digitizer NI5154 to start a multirecord acquisition by sending a start trigger. Currently I use the timestamp of the first captured waveform as the trigger time. This is not a precise approximation since the time difference between the first waveform and the trigger varies in a few ms range.
Anyone know how to read the trigger timestamp?
thank you.
Lixin

Hello,
The timestamp that you're looking at is actually the software timestamp returned by the NI-Scope driver VI, so you're right that it will differ from when the start trigger on the digitizer hardware is received and when that first sample is returned in software, especially if you have a very long record length.
There are two properties that can help you determine a relative timestamp between records, but is actually a time value of a constantly running counter onboard the digitizer. The "Absolute Initial X" and "Relative Initial X" values that get returned as part of the "wfm Info" on the Fetch VI, will show you the timestamp of the first sample in each record of a particular acquisition and the time from the trigger to the first sample of the record, respectively. Take a look in the niScope Fetch (poly) detailed help and you can see this explanation.
These values are good for comparison between records, but not a good absolute timestamp, because this counter is constantly running and is only reset on rollover or when the board is reset. So, you can see that the values returned may look a little funny, but keep in mind they are values derived from the counter counting a certain rate. So, what you can do is take the first values returned for AbsoluteInitialX and RelativeInitialX and add/subtract them (depending on your trigger type) and make that value your "0" time, and then for each consecutive record, just extrapolate from there.
Hopefully this helps out.
Chris W

Similar Messages

How to calculate the time between start trigger,first scan and first A/D in DAQ

Environment: Labview 6.1, N6052E DAQ board(max scan rate=333KHz, max channel rate=333KHz, settling time=3.5usec+1LSB)
I am using external scan clock 10K scan/s collecting data on 16 AI channels, and external channel clock 200KHz.
Could show me how to calculate the time betweent he start trigger, the first scan and the first A/D conversion?
Thanks

I read the one you give to me. still cannot work out. I am using Labview 6.1 DAQ vi, including AI config.vi. clock config.vi, AI control.vi, AI read.vi, working on colect data on 16 AI channels. So I belong to SCAN function and external scan and sampling timing, right?
But it says the T1 and T2 are determined by external signals. How can I calculate that?
T1=1/10KHz or T1=1/160Khz?
T2=1/200KHz?
Is the above correct?

Producer Consumer Start Trigger

Short Explanation: I'm using a 3rd party device to send a TTL signal to use as my start trigger in my VI. My cDAQ and modules appear to have the ability to send a start trigger independantly but I have been unable to hunt down how to do this in a producer/consumer system. I do have an idea at the bottom of the long explanation.
Long Explanation:
I'm running a test system that monitors the pressure wave from a hydrogen/oxygen ignition. Components are a cDAQ-9188 with modules 9222 (x3 high speed AI), 9481 (x2 relay), 9402 (x1 I/O Module), 9221 ("Low" Speed AI).
Based upon recommendations in this forum I've placed my DAQ in a producer/consumer architecture.
At this point the system mostly works, I still have a few more things to add for all the information I want to collect. However, it records at high speed and the 9221 and the 9222 modules are synchronized. It has successfully collected good data as of this writing.
When the system starts it will monitor, but not record. I need to fill the test structure with gas to a specific concentration before I ignite/record. When I press the record button I send a TTL signal from the 9402 to my high speed camera and I close a relay on a 9481 which engages a spark system. The spark system takes a variable amount of time to charge and fire so I have a timer that leaves the TTL and the relay active for a half second.
My problem, and it's a small one, comes in with the monitoring system and the synchronization. In order to get the system to synchronize properly I had to generate an external pulse into PFI0 to use as a trigger. I attempted to assign the various clocks available as a start trigger but I ended up with unsynchronized data.
Is there a way to generate a pulse on my 9402 to use as a trigger? It feels silly to me to use an external device when I have something that can generate the signal I need.
In thinking about this post I might have solved my problem, at least in my head. I'm thinking I can move the TTL output VI (which I will eventually change to DAQmx) into the producer loop and move my true/false statements to the consumer loop as a 1D array within my queue to start the record. Probably more to it than that but I can only learn by experimentation right?
Thoughts? Recommendations?
VI attached.
Solved!
Go to Solution.
Attachments:
HUCTA Controls.vi ‏186 KB

You can't generate a pulse with the 9402 itself. The pulse would actually be generated by the 9188. You should create a Counter Output task to generate a pulse train. Try the attached example as a start point to experiment with the counter.
This Vi is for LabVIEW 2013, if you have an older version let me know and I will try to convert it.
Camilo V.
Applications Engineer
National Instruments
www.ni.com/support
Attachments:
Pulse Train Generator.vi ‏18 KB

Timer fires during trigger processing on web

I was looking for a way to augment the default behaviour
of a hierarchical tree. The trouble is clicking in a tree can fire various combinations of WHEN-MOUSE-CLICK, WHEN-TREE-NODE-SELECTED, WHEN-TREE-NODE-EXPANDED,
WHEN-TREE-NODE-ACTIVATED, WHEN-MOUSE-DOUBLE-CLICKED. I wanted to trigger some action after they had finished firing but as I didn't know which would fire last, where to put the code ?
The solution I found was to start a 1 ms timer in WHEN-MOUSE-CLICK (which always fires first), gather information from the other triggers into a variable, and do my processing in WHEN-TIMER-EXPIRED. This worked fine on client/server but when I deployed it on the web I found the timer expired between WHEN-MOUSE-CLICK and WHEN-TREE-NODE-SELECTED (triggered by a single click).
My understanding of timers is that, however short their duration, they should not expire during trigger processing. Have I got this wrong or is this a bug ?
It seems to work OK with 5 ms but I would like to know what is going on.
(f6i patch 7)

All,
as promised, here's an answer from development. Duncan said it already, but here's the long version
1). Regarding timers in general. 1ms timers fire on the server (effectively,
at the time the timer is created in a trigger, we put a timer macro on the
stack so that that next time we go for input (after we've processed all
of the events we've already gotten at that point), it will act as if the timer
has expired. This, as you know, prevents us from doing round-trips to the
client when people are simply creating a timer to get around some of the
restricted built-in/trigger issues. Any timer of longer than 1ms will get
created on the client and thus cause round-trips. We have no plans to
bump that threshhold up, so people could use 2ms timers if they wanted...
2). Regarding timers expiring during trigger processing. It is true in both
client/server and web that we will not expire a timer while a trigger is
firing. However, the order in which the user will see events (and thus
which triggers will fire in) can vary. In the example that was given,
the user (double)clicks on a node in the tree on the client. The first
mouse click causes a message/event to be sent immediately to the
server, which ends up causing the when-mouse-clicked trigger to fire.
As soon as that message is sent, the server starts processing that
trigger. In the meantime, the client may decide that it needs to send
other messages (such as when-node-selected, etc.). However, until
the server sends a return-message to the client asking for more input,
this won't get sent. Now, the server fires the when-mouse-click trigger,
and as part of it a timer gets created. There are two possible scenarios
here.
In the first scenario, the timer is 1ms, and thus is handled on the
server. Thus, when the trigger ends, the server sees if there is any more
input to be processed, and sees that the timer has expired (because, as
I explained above, this gets put directly onto the macro stack). Thus, the
timer expired trigger fires. After that trigger fires, the server sees that it
has no more input waiting, and sends a message to the client telling it to
send more input. At that point, the client can send whatever other events
it has queued up (such as the when-node-selected) and we carry on.
In the second scenario, the timer is more than 1ms long. In this case, when
the trigger says to create a timer, the server queues up a message to send
to the client telling it to create a timer. When the rest of the trigger is complete
and the server sees that it has no more events to process, it sends this timer
creation message to the client at the same time it asks the client to give it
more events. The client sends the when-node-selected event, the server
processes it, and eventually asks the client for more input. By then, the
timer has expired and then the timer message gets sent to the server.
In neither of these cases does the timer trigger fire in the middle of
another trigger that is already firing, it is simply that the separate triggers
might fire in a different order because of the order that the underlying
events are processed. In client/server, the process is effectively the same
as the 2nd scenario above, because the timer is handled by the toolkit, just
like the other events, and thus the message for the timer expiring will get
sent to Forms after any of the events related to the mouse click. But again,
the rule about timers firing during trigger processing is not violated, it is just
that there is a break between triggers that can allow a 1ms timer to fire
'sooner' on the web than in client/server.
Fran

Using DAQ occurrence to wait for start trigger

Hi,
I'm trying to use digital triggers to start and stop datalogging. Every time start trigger appears, new file is created and data is acquired to file until stop trigger occurs. Now I'm using set DAQ occurrence and wait for occurrence functions to wait for start trigger before creating a new file. The problem is that after first stop trigger this occurrence method doesn't work. I believe it's because AI is not cleared and configured before calling DAQ occurrence again. Number of scans acquired is not zero, if I don't clear and configure AI again? Am I right?
Do I have to clear and init AI everytime before occurrence config or is there a better way to make program wait for start trigger?
Thanks in advance,
Jakke

Hi Matt99eo,
Have you configured your device for triggering? Although you have not mentioned your device specifically, the M series user manual provides a great explanation of digital triggering. Using the DAQ Assistant, this can be configured from the triggering tab. Hopefully this helps!
Regards,
h_baker
National Instruments
Applications Engineer
Digital Multimeter Resources

Working of start trigger

i want to know how a start trigger starts the acquisition of data.please give me any example

Hello Christian,
Thank you and Best Regards,
I implemented a advance Measurement and Control system using cRIO-9074
with c-Series I/O cards( NI 9217, 9411, 9264)
I have some questions about it,
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I saw your post in NI discussion forum about how to write data from
Host.vi, But still I am confuse that how can I creat a protocol between
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38 channel to write data.
(3)- I have to measure time difference between two digital pulses, to find
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i get a timestemp when there is risisng edge for the second rising edge
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I am stuck in this question since from last one month. I already followed
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is may be wrong.
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CTR start trigger error - USB6343

Hi-
A digital pulse from a device in my system is connected to the gate of CTR0 (PFI9).
CTR0 is used as a quadrature encoder. My code routes PFI9 to the gate of CTR1 (PFI4)
and also defines PFI9 as a start trigger for CTR3. CTR3 is set to generate a finite
retriggerable pulse train for each digital pulse on PFI9.
My code returns error -89137 indicating that Specified route cannot be satisfied,
because it requires resources that are currently in use by another route.
Not sure what this means?
Screenshots of relevant code and error message are attached.
I am using LV2010 and a USB-6343.
Your help is appreciated !
Dar
Solved!
Go to Solution.
Attachments:
CTR3 start trigger code.jpg ‏89 KB
External trigger pulse route and CTR1 setup code.jpg ‏129 KB
Error.jpg ‏163 KB

Hey Dar,
As long as you're careful about managing your hardware resources then you shouldn't face persistent problems. It's just a matter of knowing which lines you are using at what time, and being conscious of how your signals are physically re-routed in your hardware (as I said, this is something you can check in Measurement & Automation Explorer). There are lots of great DAQ resources online through NI KnowledgeBase articles, Developer Zone articles, and community examples (found at ni.com/support). For resource related conflicts, this KnowledgeBase article is particularly good:
http://digital.ni.com/public.nsf/allkb/485201B647950BF886257537006CEB89?OpenDocument
I hope this helps! If you encounter future problems, the forums are a great way to get peer input &/or response from NI engineers.
Courtney L.
Applications Engineer
National Instruments

PXI question: four analog ouput cards to start-trigger simultaneously

Hi all,
Here's the situation:
We have built a system that ouputs 24 analog signals using a PXIE-1073 chassis. It has 5 slots:
Slot 1:          Internal
Slot 2:          Empty
Slot 3:          Empty
Slot 4 (Hybrid): PXI-6733
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I can't speak to the chassis, but I'd warn you that if you want your tasks sync'ed, you'd better share a sample clock too and not just a start trigger.  The onboard clocks will have a tolerance (often ~50 ppm, dunno for your 6733's) and their sampling instants will drift apart from one another over time. In fact, I rarely both with triggers at all for syncing tasks & boards. I'll usually *only* share a sample clock, and then make sure I start all the slave tasks before the master whose sample clock is being shared.
Good luck on your real question though...
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Start trigger 6608

Program works in CVI 8.0
I use several 6225 for analog acquisition and one 6608 for time metering.
For simultaneous start of all devices start trigger must be set up.
DAQmxCfgDigEdgeStartTrig function allows me to connect ai\StatrTrigger of "master" 6225 with PXI_Trig0 and to connect ai\StartTrigger of other 6225 with DevN\PXI_Trig0.
So, one of 6225 defines strarting others devices 6225. For complete syncronization I must tune up start of 6608. This mean, that I shall connect PXI_Trig0 with DevN\Ctr0StartArmTrigger, where DevN - name of device 6608 in system.
What function must be applied for it? Maybe I need fundamentally other method of syncronization?
Best regards, Alexander

Hi Alexander,
To define the source terminal of the Arm Start Trigger in LabVIEW, use the DAQmx Trigger Property Node (see attached image). The C function for the same operation would be DAQmxSetDigEdgeArmStartTrigSrc(). Is this what you're trying to configure?
Regards,
Andrew W
National Instruments
Attachments:
trigpropnode.JPG ‏25 KB

Set time at start of DAQ to 0

I am using 'DAQ Assistant' (subVI) to measure some AI's I am then storing this data using 'write LVM'(subVI). I acquire for a length of time when a trigger is received, it then stores and waits for the next trigger where the process is repeated. When I look at the LVM file I see that the time axis doesn't start at 0 seconds. I think the time actually starts when I start the program running because as you look at the files sequentially the start time always gets bigger, although I am not sure as I am only using express vi's so it all quite elusive and clever and not in my control. In order for my time axis to start at 0 seconds what do I need to reset.
Nice

Hello,
I have had this post in my inbox for a few days and have been checking to see if you have posted further questions or if the posts from other users helped you out enough to get moving again with your project.
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Arrive time of start trigger

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