How to trigger a TTL output with an analog input

Hello,
I have an apparatus for measuring the flame speed of various hydrocarbon/air mixtures. The chamber uses central ignition as the means for igniting the mixture. My goal is to film the ignition process with a high speed Phantom video camera. I control the ignition with an analog output signal from a SCC-68 DAQ. I would like to trigger the camera with the same signal that triggers the ignition sequence. The camera is triggered with one TTL pulse so ideally I would connect the output analog voltage signal to an input analog voltage port that would be used to trigger a counter output that generates one pulse.
I have a sample VI that triggers a digital pulse each time the analog trigger level is met and it works for what I am trying to do but I do not understand how the two channels are connected. I also can't figure out how to make the VI end after just one pulse. In the VI the digital counter is supposedly triggered using the /Dev1/ai/StartTrigger slot on the DAQ but nothing is connected to this slot.
I need to first figure out how to make the output_pulses_on_sine_wave.vi terminate after a single pulse is generated. Then I can try to incorporate it into the VI that I use to control the ignition and measure the temperature and pressure once the mixture is ignited.
John
Attachments:
output_pulses_on_sine_wave.vi ‏27 KB

I am using the USB-6259, sorry for the confusion. I would be nice if I could trigger with an analog signal to the ignition system but it is controlled with a high voltage relay that operates when 12 volts are supplied to it. It really isn't a trigger as much as powering on the high voltage relay. To control it, I have a 12 V supply line that is switched closed using a SCC-RLY module. Could I somehow connect the 12 V supply to one of the buses and use a digital trigger to supply the 12V on command to the high voltage relay?
Thanks for the quick response.

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I'm fairly new to LabVIEW and I'm trying to collect data from multiple sources with synchronized timing on the acquisition but I'm having trouble figuring it out. My problem is that I've got two counter frequency inputs, one optical tachometer reading one pulse per revolution, and a max machinery flow meter with a k factor of 12000. I can't seem to figure out how to sync the timing with my multiple analog inputs. I've been attempting to get the tachometer to sync with the analog inputs first by following the example linked here. (https://decibel.ni.com/content/docs/DOC-10785) So far each time I run it I either get a timeout error on the DAQmx read or a "Multiple sample clock pulses were detected" error (see attached image). It seems if I slow the sampling rate way down to say 10 hz and ensure that the tachometer signal is over 800-1000 RPM (13-17 Hz) before starting the VI then the program will run without errors until the RPM drops below that threshold then the "Multiple sample clock pulses" error occurs. The code is attached below.
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Thanks!
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Solved!
Go to Solution.
Attachments:
SimpleDAQ.vi ‏44 KB
LV_Error.JPG ‏31 KB

Maybe third times the charm?
So I've finally got a good handle on why the VI is having problems at low RPM though I'm somewhat embarassed how long it took me to do that
Because I have the counter time synced to my Analog input task if it doesn't see at least two pulses between the two clock pulses set by the analog input task I get the -201314 "Multiple sample clock pulses" error. This seems fine at first as it just sets a minimum RPM that I can measure and it's well below the area I'm interested in so no problems there. I tried a simple error handler that would clear the error when it happend assuming the loop would keep iterating until the RPM went above that minimum at which point I would get a signal again. This is not the case, the read function just continues to spit out the -201314 error even after the RPM is back in the readable range. So then I tried adding two case structures so that when the error occured it would stop the task, clear the error, and then start the task again on the next loop iteration (Code Attached). This also doesn't work as the error shows up again on the stop task and then AGAIN on the start task on the next loop iteration. It seems this error is not actually being cleared and once it happens it stays with the task regardless of what the error cluster is carrying.
Anyone have any ideas? The only solution I can think of is to just clear all tasks and recreate them each loop iteration until the RPM is readable again but that strikes me as a horribly clunky solution.
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SimpleDAQ_1_Start Stop.vi ‏48 KB

Control analog output based on analog input

Dear forumers,
I am pretty new to the labview programming so excuse me if this was posted before.
I use: Labview 8.5 + PCI 6229
I want to create a real time feedback: to control analog output based on analog input. The task is very simple - if the ai1 (analog input 1) voltage is larger than a constant, then decrease the voltage of the ao1 (analog output 1) by a constant. Otherwise increase the voltage of ao1 by the same constant.
All should work for 10 seconds.
I have tried to implement this using 2 daq asistants and various methods. The problem is that I get the whole signal recorded from the ai1 ( 10 seconds) and then modified and released to the output (another 10 seconds). The execution takes 20 seconds instead of 10 and it is not realtime at all.
Is it a must to make vi in "run continuous" mode to make it work ?
Please help :}.
I am attaching 2 examples.
1. Main idea what I am trying to accomplish
2. Very simple example that still does not work in real time simultaneously.
Attachments:
example-main.vi ‏180 KB
example-simple.vi ‏147 KB

nooto wrote:
Thank you for your suggestion.
I understand the simple arithmetic you are talking about. However I do not understand why it takes 20 seconds instead of 10 to complete the task. In other way to say - why it reads the whole input first (10 seconds) then write the output ( 10 seconds).
Why doesn't ir read and write simultaneously?
If I use Elapsed Time function - what feedback response time can I expect ? Is it good to use Elapsed Time if i need fast response time? In my application i would I need about 1 milisecond response time. Currently in the example the rate is 50 Hz, later I would like to change the rate to 1000.
You simply don't understand the underlying paradigm of LabVIEW -
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How to send a ttl signal with a good exactitude less than 10ms?

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Hi guys,
I am a beginner in Labview and have been dealing with this problem for a couple of weeks now and just can't seem to get it completely right, I have a feeling there are a few small bugs in my code/hardware setup.
I am running an scxi-1000 chassis with a 1600 module and 1302C along with a 1303 accesory for temperature measurements, this is connected to four thermoucouples. Unfortunately I have a limited number of modules available so I am also using a PCI-6221 DAQ card with an scb-68 breakout box used for a digital output and analog input voltage channel. Attached is my labview program. When I run the code at a 50 Hz sampling rate it runs with no errors but the data file comes out extremely wrong, this is also attached. When I run the code at 100 Hz I get error-200279 after a few loops. I used to have 2 daqmx timing VIs (one for each input), but the same error would eventually happen, I have also tried increasing the buffer size on said timing VI. I am also using an old computer (Pentium IV) could this effect the program?
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Attachments:
tc_2.txt ‏1102 KB
FinalCombined_2.vi ‏128 KB

Ok this makes sense. I have made the suggested modifications but still getting the same error with sampling rates of 100 Hz or higher. Could you check that I have implemented the queue VIs properly (new file attached)? Also when running at 50 Hz in debug mode it does not look like the second while loop (with the dequeue element) comes into play until I hit the stop button, once I hit the stop button I get the following error:
Error 1 occurred at Dequeue Element in FinalCombined_2.vi
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LabVIEW: An input parameter is invalid. For example if the input is a path, the path might contain a character not allowed by the OS such as ? or @.
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NI-488: Command requires GPIB Controller to be Controller-In-Charge.
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FinalCombined_2.vi ‏102 KB

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LV7.1
DAQmx
PCI-6036E
SC-2345
Windows 2000
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column 2
column 3
1
12345678
100
2
44
2
12345678
100
3
13.87
3
12345678
100
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12345678
101
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14.35
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12345678
101
4
14.35
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102
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12345678
102
4
14.83
8
12345678
103
3
0.95
9
12345678
103
4
0.95
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column 0
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1
12345678
100
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100
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102
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102
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14.83
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102
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0.95
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12345678
103
2
0.95
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12345678
103
2
0
15
12345678
103
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0.95
16
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103
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How to trigger a TTL output with an analog input

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