No pulses generated!

Hey!
I am having trouble with generating a PWM signal using a counter channel on our NI-6733 card.
I use the DAQmx VIs to: Create a task (frequency = 50 Hz, duty cycle = 0.07) - set the task to finite samples with a certain number of samples - start the task - wait until they've been written - stop the task (is that actually necessary?) and delete the task.
I check the output with an oscilloscope. If I run the VI, only some times the pulse train is generated and sometimes nothing happens.
The same happens when I use MAX and create a pulse train with the "test panels" dialog.
It seems to me like there's a hardware problem, how can I investigate what's the problem?
Does anybody know this issue? Am I doing something wring? Thanks for any help!
Best,
Steve
Solved!
Go to Solution.

Hey again!
This was my bad! The osci was just to slow. Once it was acquiring the signal when the puls was on its high state and the other time it acquired the signal when the pulse had its low state..
Cheers!
Steve

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Hello, all,
I need to design a Labview problem as a Multi-channel Sequential Controlling Pulse Generator and output through DAQ card. The required digital pulses are showns in the attachment. Time scale values are shown on the top as an example. CLK's duty cycle is 0.5. x1 and x2's value need to be programable.
Could anyone give example codes? Or, give me any idea to program these pulses?
Attachments:
clock.png ‏22 KB

Duplicate
http://forums.ni.com/t5/Multifunction-DAQ/Multi-channel-Sequential-Controlling-Pulse-Generator-Desig...

Pulse Generator

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Hi Jack,
Thank you for your reply. I was looking over the topic you directed me to and will continue to do so. I had install DAQ as it wasn't previously installed. I had a few questions regarding that.
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Hi Gopal,
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Attachments:
1d.vi ‏77 KB

hi Tiano,
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I am attaching a copy of this mod
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hope this helps,
Lalitha.
Attachments:
fast2-vel_change.vi ‏156 KB

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Eric P. Nichols
P.O. Box 56235
North Pole, AK 99705

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Measure_Rink_(sub)6b_2ice.vi ‏73 KB

Greetings,
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Continuous Waveform Acquisition Using Scan Clock Gating
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Attachments:
gpctex5.cpp ‏10 KB

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Hi Naveen,
I apologize that I did not post sooner. I have determined that this is not directly possible. I am actually currently looking for a workaround. This workaround should be possible but may not be all that straightforward to implement. I will post back as soon as I find something.
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My motion control system is driven by a 6602 I wanted to acquire analog current (to a voltage via I/V converter) from a 6024 AI when:
(1) At the start of the pulse generation
(2) Stop at the end of the pulse generation
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(4) Option to skip at regular intervals to reduce amount of data accumulation
Anyone have some suggestions? What I did try and attempted was to "loop an AI from a triggered intermediate Analog Input VIs" this is rather erratic!My question for the analog input software are:
(1)Can you trigger an AI to start a continuous acquisition?
(2) How do you do AI from a "start" p
ulse train to "end" pulse train?
(3) How do you manage time for File I/O meanwhile doing (1) and (2) above?
Bernardino Jerez Buenaobra
Senior Test and Systems Development Engineer
Test and Systems Development Group
Integrated Microelectronics Inc.- Philippines
Telephone:+632772-4941-43
Fax/Data: +632772-4944
URL: http://www.imiphil.com/our_location.html
email: [email protected]

"(1)Can you trigger an AI to start a continuous acquisition?
(2) How do you do AI from a "start" pulse train to "end" pulse train?
(3) How do you manage time for File I/O meanwhile doing (1) and (2) above?"
Answer 1 and 2)
Yes you can, This VI is part of the search examples that ships with LV:
"Continuous Acquisition & Graph Using Digital Triggering and External Scan Clock
Demonstrates how to continuously retrieve data from one or more analog input channels using an external scan clock when a digital start trigger occurs."
Go to Search Examples in the Help/Contents of LV. Then pick I/O Interfaces/Data Acquisition (DAQ)/Analog Input/Triggering an Acquisition/Triggering a Continuous Acquistion.
This VI is appropriate ifs you want to clock the DAQ with some clock (external scan clock) other than the on board clock.
The start trigger required by the DAQ card will be a TTL signal attached to the PFI0/TRIG1 pin of you DAQ card (via whatever signal conditioning you have).
The external clock also needs to be TTL and is attached to the PFI7/STARTSCAN pin.
You tell it which AI channel to use and wire that up appropriately.
All of this stuff is in the context help for the VI.
Answer 3)
You have a misconception of how the acquisition makes its way into a file on the hard disk. You don't really "stream to disk." The VI above will run a buffered acquisition. The DAQ card sets up a buffer that fills with the data continously. When you use the VI you set up how the buffer is configured, you will see controls for buffer size, number of scans to read at a time, etc. The acquisition runs data into the buffer continously and reads from the buffer are a parallel process where chuncks of the buffer are extracted serially. You can end up with a scan backlog where the reads are falling behind the data. Making the buffer bigger helps. All of this is limited by the sampling capability of the DAQ card. 200kSamples/second is for one channel of AI. Divide by 2 for 2 channels. etc.
The short answer is that the VI and DAQ card manage the file I/O for you.
The VI above writes the scan out to the waveform chart on the front panel. You will want to wire that data out from the AI Read Sub VI to a spreadsheet file in tab delimited form or similar.
Look inside the VI block diagram. There is a While loop containing the AI Read. Every time the loop runs (unless you hit STOP), the AI Read plucks the specified # of scans from the buffer (starting from the last unread datum). If you wire the double orange wire from AI Read out of the loop (and set the tunnel for Auto Indexing) the Vi will build another buffer in memory that is a series of AI Reads appended to each other, a sequencial record of the acquisition. Here you put in a Write to Spreadsheet VI. This is in the Functions Pallete, it is the first VI in the File I/O Pallette (icon looks like a 3 1/2 disckette).
There is more to it than this. The spreadsheet Write is 1D or 2D only. By running the array out of the while loop with auto indexing enabled, you create a 3D array. (If you turn off auto indexing you will only get the last array performed by the AI Read.) You will need to create a new array withe the pages of the array placed serially into a 2d array. I don't think I want to get into that. It isn't that bad to do, but you should get some time messing with arrays on your own, then you will see how to do it yourself. One solution is to only run the While loop once with a buffer big enough to hold the whole acquisition, or in other words no loop at all. I don't know how many scans you want. The other thing is by wiring that AI Read out of the loop you are creating an array that must be dynamically resized as the loop runs. Kind of a no no. Better to know what you are acquiring size wise and letting the VI set up buffers and array space that does not need to be changed as the program runs.
Caveat: I am fairly new to this and I could be wrong about the arrays and buffers and system resources stuff. However, I have done essentially what you are trying to do succesfully, but not "continuously." I limited the AI Read to one large read that gets what I need.
"Continously" is usually reserved for screen writes as in the VI above. The computer is not required to continually allocate space for an ever expanding array to be written as a file later. Each time this VI runs the While Loop the data goes to the waveforn chart. Each new AI read overwrites the previous one. Sort of like if you turn the Auto Indexing off. When the VI stops, the waveform chart on screen would show the same data as was written to the spreadsheet.
Feel free to email me directly: [email protected]. I will help as I can.
Mike Ross

Generating a pulse sequence in NI5401 board

Sirs,
I?m sending this email massage because I have a doubt concerning NI 5401 Function Generator Board.
I?m working with a PXI system together with a NI5401 board, and I want to generate a pulse sequence with this board.
The propose of this is to synchronize my pulses with the acquisition of data by another board (PXI board from Goeppel ? Boundary Scan board which has 4 I/0 ports of 8 bits)
I want for each pulse generated to acquire and transfer data in that board, thus I need to know how can I send a predetermined sequence of pulses, (N pulses and then stop). (attached I send a figure to illustrate my question)
Please, I tried to understand the triggers but....
If the triggers is the solution for my probl
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Note: Now I'm generating a sequence of pulses using a simple pin I/O of the Goeppel Board but the problem is if I run many Labview applications sometimes the software is not fast enough to generate that pulses. Then I think if I use a hardware solution, like in the 5401 board,I could get faster a better responses for my pulses. Note that I'll need to now, in each instant, how is the level of each pulse.
Note2:I'm using LabView6i software.
Thanks very much.
Attachments:
PULSE.jpg ‏25 KB

Hi
The NI 5401 is a Function Generator; this is significant in that it is made to make periodic waveforms such as Sine, Square, and even a user defined periodic waveform that a user can download (the 16K buffer). The board can be triggered to start generation, and with a software call, abort generation. But there is no hardware that can specify how many cycles of a waveform has been generated to control the number of cycles at the output.
Depending on the rate of the pulses you need, it may be possible to do something. A pulse train is essentially a square wave with a certain duty cycle. Set up the device for a certain frequency that matches the rate of your pulses, and program it to start with a Software trigger. The best output to use is the Sync output which w
ill give you a TTL pulse.
After the software trigger is called in your code, use the Wait VI to wait a certain amount of time that corresponds to the number of cycles/pulses for the signal that you need, and then after the wait, immediately call NI-FGEN Abort to stop the output generation.
If you are unable to control the number of pulses through software, the NI 5401 really isn't made for this operation. The NI 5411 Arbitrary Waveform Generator is the device made to do this, create the pulse waveform you need, select how many times you want it to "loop", and then generate a waveform of zero volts. The NI 5411 has the hardware to count number of loops, and trigger, etc.
I hope this helps.
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No pulses generated!

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