Simultaneous tasks using DAQmx functions

Hi all,
Is there any example of DAQmx PCI-6251 on Labwindows in which Multithreading is used.
Basically i want to acquire and generate Analog signals from PCI-6251 by using Multithreading.
In which one Thread is for Acquiring the analog signals and the other thread is for generating
the analog signals after performing some calculations on the samples of the Acquired Signals.
So it means i dont want to Acquire and Generate analog signals Simultaneously but there must be a
"Little Delay" between the two Threads.
Any help on this topic will be Greatly appreciated.
Regards

Actually, this is entirely possible. The primary difficulty is sharing data between your two threads. The easiest way to accomplish this in LabWindows/CVI is with a thread safe queue.
I admittedly don't write much DAQ code, so it likely won't meet your specific needs, but I've attached a simple example of doing what you've asked about. I create two threads, one for reading and one for writing. Each thread creates a task, and then loops while reading or writing until told to stop. They share data through a thread safe queue.
Let me know if you have any questions regarding the sample -
NickB
National Instruments
Attachments:
DAQMTProcessing.zip ‏7 KB

Similar Messages

Editing channels in a task using DAQmx in Labview

Dear All
A few days back while I was trying to build an application to dynamically change my tasks in Labview ,I have encountered the following problems
1)MAX is allowing me to configure multiple channels onto the same physical analog input channels.(Which later i found was a bug in MAX)
2)At times when I try to read the "Channel names configured from the Tasks that have been created , I get the following error
Task is either invalid or does not exists"
3)Also I am trying to edit the channel properties such as range and scale values thru Labview but I am not getting any function to edit channels.There is only one function called "Create virtual channel"
Can somebody help me?
Thansk and regards
Pooja Malhotra

Pooja,
1.) The ability to create, what I assume is multiple global channels, all referencing the same physical channel, is not a bug.
2.) Are you trying to read the name of a task created in MAX or in
LabVIEW? If you are reading a MAX task, this error could occur if the
device is not present. If you are reading a LabVIEW task, this error
could occur if the task has been cleared.
3.) Prasad is correct. All of these attributes are available with the various DAQmx property nodes.
Does this answer your question?
Ryan Verret
Product Marketing Engineer
Signal Generators
National Instruments

Using DAQmx functions without installation

Good evening everybody,
I have an instrumentation problem linked to DAQmx. I would like to communicate with an instrument using NIDAQmx tasks. I use an environment program system : visual studio 2003. At the end, I want to produce a dll. This dll, I want to put it on another computer. The question is the following. If I want to launch the dll by calling it, will I need NI-DAQ on the other computer or a software to use the dll ?
When I tried to produce an exe with a VI, I needed to have Labview RunTime to launch the exe. If I want to launch the dll, will I be able to use the dll alone on the computer, without the installation of NIDAQ. Can I use the tasks only with the dll (since I need Run Time for the .exe, do I need Run Time also). ?
I am sorry, it must be not clear. But I am available to explain you more the problem.
Best regards.
Thank you.
gautier
Solved!
Go to Solution.

Since you have LabVIEW installed on your computer, the Run-Time is not required for running LabVIEW executables.
But if you decide to use your LabVIEW executable on an other computer, you will need to install the LabVIEW Run-Time on it. You can also build an installer which will contain your program and addtionnal components (such as LabVIEW Run-Time and required drivers). Building an installer avoid to download and install the components separately.
For more information regarding installer, you can look into LabVIEW's help (Building an Installer (Windows)) or follow Core 2 training course.
If your program uses NI-488.2 driver, you will need to install it on your computer.
Installing LabVIEW Run-Time is only required if your program which contains DLL calls is a LabVIEW executable.
Regards,
Jérémy C.
National Instruments France
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Travaux Pratiques d'initiation à LabVIEW et à la mesure
Du 2 au 23 octobre, partout en France

Pretriggered plus posttriggered Using DAQmx functions

Dear Sirs,
In the propel.vi which is attached, laser is used in the channel Vi0 to start the mechanism of trigging to acquire posttriggered samples from the analog signal in the channel Vi1 successfully. I would like to know what changes I need to do in the block diagram to acquire pretriggered plus posttriggered samples from the analog signal in Vi1?
Thank you for your help.
Oscar Delgado.
Attachments:
propel.vi ‏34 KB

Hello Christian,
Thank you for your reply. According with your suggestion I found in the examples file of my LV the Cont Acq & Graph Voltage – Analog SW Trigger.vi, which I am using successfully to acquire pre triggered plus post triggered samples.
Thank you for your help.
O. Delgado.

Qns on DAQmx function

i am currently using ATMI force and trying to use VB6 to get the reading for the six analog channel in realtime..
I keep seeing ppl use daqmx function.. but i dont have that in my library... i have install NI -DAQ 7 and measurement studio..

Do any one have program that run muti analog channel by not using daqmx.. using traditional code

Would you Open and Close DAQmx tasks within a function or Globally

Hi Guys,
This should start something.
The subject is DAQmx Tasks.
If you were writing a function that is called many times, say MeasureVolts (double *Value) to obtain a reading from an Analogue Input Channel.
Would you.
1. open and start the task inside the function, do the measurement and then close the task inside the same function.
or
2. open the task globally and later do the measurement inside the function using the global task then close the task only when the application is closed.
I am mostly concerned with the overhead of task generation and closing, what do you guys and girls out there do?? and what is the general opinion?
I would appreciate your views.
Regards
Paul.

I would definitely NOT keep configuring and clearing (I think that's what you mean by open and close) the same task over and over. I would configure once, read many times in my main app, then stop & clear once.
I typically like to package such data acq into an "Action Engine" that keeps track of its own DAQmx task id so I don't need to sling that task id wire around into multiple parallel loops / vi's. Attached is a very stripped-down example for Digital Input.
I would typically do more with error testing and would make the "Action" enum into a typedef custom control, but this gives you the basic idea. The action engine approach works very nicely when there's a small # of different kinds of input parameters and output info needed to support all the necessary action cases. When you start needing a large number of differnent kinds of inputs and outputs to support the desired actions, then you start having difficulty with (1) having enough terminals to wire and (2) remembering which inputs and outputs are meaningful for which actions.
-Kevin P.
Attachments:
DI Action Engine.vi ‏75 KB

How to use a multiple boards (6321/6323) analogical acquisition task with simultaneous analogical generation task using the same boards (Labwindows CVI10)

Subject : it seems impossible to run a multiple boards analogical acquisition task with one or several analogical generation task using the same boards.
NI Configuration : Dev1 = Dev2 = 6321 boards
Development environnement : LabWindows CVI 10
Source code for analogical acquisitino task :
       DAQmxCreateTask("",&AIRecordingtaskHandle);
       DAQmxCreateAIVoltageChan(AIRecordingtaskHandle,chan,"",DAQmx_Val_NRSE,min,max,DAQmx_Val_Volts,NULL);
       DAQmxCfgSampClkTiming (AIRecordingtaskHandle, "", rate, DAQmx_Val_Rising, DAQmx_Val_FiniteSamps, sampsPerChan);
       DAQmxGetTaskAttribute(AIRecordingtaskHandle,DAQmx_Task_NumChans,&gNumChannels);
Chan = "Dev1/ai0, Dev1/ai1, Dev1/ai2, Dev2/ai1"
Source code for analogical generation taskS :
       DAQmxErrChk (DAQmxCreateTask("",&AOtaskHandle_C1_DAC0));
       DAQmxErrChk (DAQmxCreateAOVoltageChan (AOtaskHandle_C1_DAC0, chan, "", min, max,DAQmx_Val_Volts, "")); // chan vaut Dev1/ao0
       DAQmxErrChk (DAQmxCreateTask("",&AOtaskHandle_C1_DAC1));
       DAQmxErrChk (DAQmxCreateAOVoltageChan (AOtaskHandle_C1_DAC1, chan, "", min, max,DAQmx_Val_Volts, "")); // chan vaut Dev1/ao1
       DAQmxErrChk (DAQmxCreateTask("",&AOtaskHandle_C2_DAC0));
       DAQmxErrChk (DAQmxCreateAOVoltageChan (AOtaskHandle_C2_DAC0, chan, "", min, max,DAQmx_Val_Volts, "")); // chan vaut Dev2/ao0
At the first DAQmxReadBinary call attempt, the system shows an error (see attached document)
What we understand about that error : it is impossible to run the two set of tasks (ai and ao) using ressources from both Dev1 and Dev2 in the set of tasks because it is not allowed to use the same Reference Clock for that.
The question is : is there a way to to that without having that kind of message?
We tried different combinations :
- Using only one ao task (on Dev1/Dac0) : same error
- Not using any ao task (only the ai task) : no error
- configuring the ai task with only channel from Dev1 : no error
- Using "/Dev1/ai/SampleClock" as internal clock for the ai task and "/Devk/ao/SampleClock" for each ao task (k standing for "1" or "2" depending of the ao task we consider) : error
Thanks a lot.
Pièces jointes :
MsgErreur NIDAQmx.JPG ‏38 KB

doublon
Valentin
Certified TestStand Architect
Certified LabVIEW Developer
National Instruments France
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Travaux Pratiques d'initiation à LabVIEW et à la mesure
Du 2 au 23 octobre, partout en France

Elvis: Is It possible to use the Function Generator and the Oscilloscope simultaneously?

Hi,
We are using the NI Elvis to output a function or a sine wave at a certain frequency and using the oscilloscope on the same board/elvis to read a modified signal. Is this possible? Can we use both the Function Generator and the oscilloscope at the same time? Please help. The oscilloscope would be reading signal from an accelerometer. Thank you in advance. We have no VI as we do not know which to use and if they are possible.

Hi,
There is no problem using the Function Generator and Oscilloscope
at the same time with NI ELVIS. Using the NI ELVIS soft front panels (Start
>> Programs >> National Instruments >> NI ELVIS 3.0 >>
NI ELVIS – see picture attached –‘NI ELVIS soft front panels.JPG’), you can choose
to open more than one instrument at a time. We do this by opening one
instrument, allowing it to begin, and then opening another. We can also program
in LabVIEW using more than one instrument at a time by placing down multiple
Express VI’s taken from the NI ELVIS pallet on the block diagram (see picture
attached – ‘ELVIS Express VI's (LabVIEW).JPG’). One note when doing this,
please see KB 41ODPHX1
for an example of how to program in parallel. If you do not wire the ‘stop’
terminal of the express VI’s, you will get the error described.
David L.
Systems Engineering
National Instruments
Attachments:
ELVIS Express VI's (LabVIEW).JPG ‏74 KB
NI ELVIS soft front panels.JPG ‏56 KB

When I acquire data using USB6008 and NI_DAQmx Base in VC++, Shall I start and stop the task in ONTimer function?

void Ctest2Dlg:nTimer(UINT nIDEvent)
   DAQmxErrChk (DAQmxBaseStartTask(taskHandle));
   DAQmxErrChk (DAQmxBaseReadAnalogF64(taskHandle,pointsToRead,timeout,DAQmx_Val_GroupByScanNumber,data,100,&pointsRead,NULL));
  DAQmxBaseStopTask (taskHandle);
If I do this, the program will halt in about half minute. But if I do not start and stop task in OnTmer function, the program will not halt and the data acquired is not corrected.
Please help me! Thanks

This is a duplicate post. Please post any new replies to the linked forum.
Samantha
National Instruments
Applications Engineer

Multiple inputs and outputs using DAQmx VIs

Hello,
I am fairly new with the LabView programming language. I have a few training books that I have been reading, and I have been following online tutorials and reading the forums. However, I have come to a problem where I don’t see a clear solution. I am using LabView 2009 (9.0f3) and DAQmx VIs.
I am using a NI 9172 chassis PLC, with two 9201 AI cards, 9217 AI RTD card, 9472 DO card, 9263 AO card, and two 9237 AI Bridge cards.
I am reading eight analog inputs with the 9201 cards, two analog RTD inputs with the 9217 card, three digital outputs with the 9472 card, three analog outputs with the 9263, and eight analog inputs with the 9237 cards.
I wrote a simple program to test one digital output task, two of the analog output tasks, and a single analog input task. I put all of them in the same while loop, and it worked perfectly. However, when I add analog input tasks to the same loop, I get an error 200022. So I tested each sensor individually by changing the channel before each run. I searched error 200022 and found that this is because I cannot start another analog input task until the previous one ends. With this said, I don’t know how to acquire an analog voltage in the same task as an analog RTD voltage. Both inputs take different constants in the start task DAQmx icon.
Attached is my test program. It is titled “Test All”. This is the program I used to test the various sensors. I tested the input sensors one at a time, and it worked fine. A few tasks are written just to test functionality, and will be added to later. The data is only displayed on the screen. I will add triggers and data write to disk functions later. This program works now, but if I add more analog inputs, it will generate the 200022 error.
Can someone show me how to correctly write the code for multiple inputs and outputs using DAQmx? All training materials and tutorials I can find all show a single input or single output, not multiples of each. Thanks for looking.
-Randy
Attachments:
TestAll-NI.vi ‏32 KB

Hi RandyC,
The Knowledge Base article Using Different Types of DAQmx Global Channels in the Same Task goes into a little more depth of what Bryan is talking about, and it also includes some example code to help show what to do.
Hope that helps,

How do I configure a counter to generate pulses using DAQmx?

How do I configure a counter to generate pulses using DAQmx?
Is says in the DAQmx C reference help
"CtrnInternalOutput—The signal at this internal terminal is where the pulsed or toggled output of the counter appears. The output of a counter pulses or toggles when the counter reaches terminal count. When counting down, the counter reaches terminal count when the count reaches zero. When counting up, the counter reaches terminal count when the counter rolls over. To configure the counter to toggle or generate pulses, use the Export Signal function/VI with Counter Output Event as the signal name."
I've tried this but can't get it to work, I may have the parameters wrong or something. The DAQmxExportSignal() function is very unintuitive to me. Here is my counter config code...
int ret = 0;
ret = DAQmxCreateTask("",&task_);
errorMsg(ret);
if (ret != 0)
throw ret;
// Configure the counter
ret = DAQmxCreateCOPulseChanTicks( task_, "Dev1/ctr0", "", "/Dev1/PFI8", DAQmx_Val_Low, 0, divider, divider );
errorMsg(ret);
ret = DAQmxCfgImplicitTiming( task_, DAQmx_Val_ContSamps, 1000 );
errorMsg(ret);
// Change to pulse mode
ret = DAQmxExportSignal( task_, DAQmx_Val_CounterOutputEvent, "/Dev1/Ctr0InternalOutput" );
errorMsg(ret);
// Start the counter
ret = DAQmxStartTask(task_);
errorMsg(ret);
The above code works fine, in toggle mode, if I just comment out the DAQmxExportSignal() part.
HELP!!!
Stefan

The problem is due to the DAQmxExportSignal call. By default, when you create a counter output pulse train task, the driver will automatically set the output of the counter to toggle when the count for each high ticks and low ticks expire. The driver also automatically routes the signal present at Ctr0InternalOutput terminal (the output of the counter internal to the device) to the Ctr0Out terminal (the I/O pin available externally). Using the line
ret = DAQmxExportSignal( task_, DAQmx_Val_CounterOutputEvent, "/Dev1/Ctr0InternalOutput" );
will tell the driver to tristate the Ctr0Out terminal and not output the signal to the external I/O pin. Using the DAQmxExportSignal function is generally only useful if you want to route the signal to some other terminal internal to the board without having the output show up on the external connector, route the signal to some other external pin other than the default pin, or if you want to have the output show up at multiple locations.
If you want to change the output behavior from toggle to pulse, you need to use the DAQmxSetExportedCtrOutEventOutputBehavior function. However, this is generally only useful if all you care about are edges (not the duty cycle of the pulse train), and you want to generate higher frequency signals. For example, with a 20 MHz timebase as the source of your counter, you can only generate a 5 MHz pulse train by default. This is because the minimum value for the low and high ticks parameter is 2 (20 MHz / 4 = 5 MHz). By changing the output behavior form toggle to pulse, you can generate a pulse train at 10 MHz since the output is now pulsing instead of toggling. However, the width of each pulse is not programmable so you will no longer have a 50% duty cycle signal. I don't remember exactly what the width of each pulse is, but I believe it's in the neighborhood of 50 - 100 nanoseconds in width. I hope this information helps.

How to use a Time - Voltage Array to Control a Analog Voltage Output using DAQmx Write VI

I have an array of Time values associate with Voltage values that I want to use to control a Anolog Votage Out Device (PXI-6251) using DAQmx. The array contains 1,000 elements. The time values are NOT evenly spaced, the rate changes through the array. The array is output once, timed to other processes.
My problem is I haven't been able to locate a reference on how to handle the timing variability in the array. If time was equally spaced I could use a loop....
The attached showes the array, first row is time (ms) and the second row is voltage (volts).
Can someone point me in the right direction?
David
Attachments:
TimeVoltage.png ‏11 KB

David,
if you have only Base version of LabVIEW, this will be a time consuming task.
If you have either Full or Professional, you will find interpolation-functions in the mathematic palette.
I am not sure which ones serves you best, but i'd startexperimenting with Interpolate 2D.
hope this helps,
Norbert
[Edit]: You could also use a polynominal fit on your voltage values. You will get a function describing the voltage over time. But you will have to modify this function to take care of the variation of time spacing. If you have a function describing your voltage over your (nonconstant) timestamps, you can simply create values for constant timeslices for your voltage.
Message Edited by Norbert B on 11-06-2008 10:21 AM
CEO: What exactly is stopping us from doing this?
Expert: Geometry
Marketing Manager: Just ignore it.

Questions about Alternate Syntax using DAQmx

Hello all,
my group has started using an alternative syntax for DAQmx Functions. Here's part of our original code:
nitWFM->AOChannels.CreateVoltageChannel("Dev1/ao0", _T(""), dMinimum, dMaximum, DAQmxAOVoltageUnitsVolts);
nitWFM->AOChannels.CreateVoltageChannel("Dev1/ao1", _T(""), dMinimum, dMaximum, DAQmxAOVoltageUnitsVolts);
nitWFM->AOChannels.CreateVoltageChannel("Dev1/ao2", _T(""), dMinimum, dMaximum, DAQmxAOVoltageUnitsVolts);
nitWFM->AOChannels.CreateVoltageChannel("Dev1/ao3", _T(""), dMinimum, dMaximum, DAQmxAOVoltageUnitsVolts);
which became:
DAQmxCreateAIVoltageChan(nitWFM,"Dev1/ao0","",DAQmx_Val_Cfg_Default,dMinimum, dMaximum,DAQmx_Val_Volts,NULL));
DAQmxCreateAIVoltageChan(nitWFM,"Dev1/ao1","",DAQmx_Val_Cfg_Default,dMinimum, dMaximum,DAQmx_Val_Volts,NULL));
DAQmxCreateAIVoltageChan(nitWFM,"Dev1/ao2","",DAQmx_Val_Cfg_Default,dMinimum, dMaximum,DAQmx_Val_Volts,NULL));
DAQmxCreateAIVoltageChan(nitWFM,"Dev1/ao3","",DAQmx_Val_Cfg_Default,dMinimum, dMaximum,DAQmx_Val_Volts,NULL));
we changed it to accommodate for a function that seemed to only work for us in one syntax (DAQmxSetWriteAttribute (nitWFM, DAQmx_Write_RegenMode, DAQmx_Val_DoNotAllowRegen))
My question is, what is the alternative syntax for the following lines?:
nitWFM->Control(DAQmxTaskVerify);
CNiDAQmxAnalogMultiChannelWriter writer(nitWFM->Stream);
because keeping them this way resulted in an error.
Your responses are much appreciated.
Solved!
Go to Solution.

Hello,
The first function can be found in the C Reference Help by going to Start»All Programs»National Instruments»NI-DAQ»Text Based Code Support»NI-DAQmx C Reference Help and expanding the NI-DAQmx C Functions»Task Configuration/Control»Advanced»DAQmxTaskControl. This explains this function and the syntax to use.
Regards,
Justin
Justin
National Instruments
Product Support Engineer - Conditioned Measurements

Creating a Scheduled Task using PowerShell v4

So here is my question. I'm trying/wanting to create a scheduled task using PowerShell v4 on Server 2012R2. I want to task to run on the 1st day of every month. The parameter for -Monthly -Day is not available. I need to use PowerShell
to create the Scheduled Task because the Task will be running with a group Managed Service Account credentials so the Scheduled Task can not be created via the Task Scheduler GUI.
Thanks in Advance

Here is a functioning task It can be easily edited in PowerShell or in notepad to alter the timing
<?xml version="1.0" encoding="UTF-16"?>
<Task version="1.1" xmlns="http://schemas.microsoft.com/windows/2004/02/mit/task">
<RegistrationInfo>
<Author>W8TEST\user01</Author>
</RegistrationInfo>
<Triggers>
<CalendarTrigger>
<StartBoundary>2014-06-04T21:31:32.0459499</StartBoundary>
<Enabled>true</Enabled>
<ScheduleByMonth>
<DaysOfMonth>
<Day>1</Day>
<Day>12</Day>
<Day>24</Day>
</DaysOfMonth>
<Months>
<January />
<February />
<March />
<April />
<May />
<June />
<July />
<August /
<September />
<October />
<November />
<December />
</Months>
</ScheduleByMonth>
</CalendarTrigger>
</Triggers>
<Principals>
<Principal id="Author">
<RunLevel>LeastPrivilege</RunLevel>
<UserId>W8TEST\jvierra</UserId>
<LogonType>InteractiveToken</LogonType>
</Principal>
</Principals>
<Settings>
<DisallowStartIfOnBatteries>true</DisallowStartIfOnBatteries>
<StopIfGoingOnBatteries>true</StopIfGoingOnBatteries>
<IdleSettings>
<StopOnIdleEnd>true</StopOnIdleEnd>
<RestartOnIdle>false</RestartOnIdle>
</IdleSettings>
<Enabled>true</Enabled>
<Hidden>false</Hidden>
<RunOnlyIfIdle>false</RunOnlyIfIdle>
<WakeToRun>false</WakeToRun>
<ExecutionTimeLimit>P3D</ExecutionTimeLimit>
<Priority>7</Priority>
</Settings>
<Actions Context="Author">
<Exec>
<Command>notepad.exe</Command>
<Arguments>test.txt</Arguments>
<WorkingDirectory>c:\temp</WorkingDirectory>
</Exec>
</Actions>
</Task>
I have edited and reloaded the XML many, many times. It works very nicely.
¯\_(ツ)_/¯

How to make a good UI for channel selection using DAQmx

A lot of my Labview programming was with earlier verisons of labview (pre Labview 7), and there are a ton of new features that I'm trying to digest (currently using Labview 8.2).
My question is (in general terms), how are people programming their UI for selecting channels and such when using DAQmx hardware? What I have in mind is a compacDAQ system with a number of modules. The user would be able to pick and choose which channels to monitor. Using MAX as part of that process seems counter intuative, and somewhat static (yeah I know you can change it there, but it feels more like something you would use for something that really doesn't change much). I'd like all the UI to be within the VI.
Are programmers using the create task VIs for that or something else?
Thanks in advance.
Solved!
Go to Solution.

I wholeheartedly second the motion to keep MAX out of the picture as far as users are concerned.
Setting up UI's for channel selection is a breeze in DAQmx when you create channels on the block diagram. The control you create off the Channels input will populate itself with the inputs that it knows are capable of performing the desired task...
<<< My configuration knows that my Module 5 is capable of doing Analog Input.
So... Just create a panel that waits for the user to select the proper channel. I also run a quick check of the user's selection before creating / starting the task. For example, if they choose ai30 or higher, and I know that the system isn't wired for those inputs, I'll not allow that selection. Also check for using two of the same input, etc.
Richard

Simultaneous tasks using DAQmx functions

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