Daqmx Sample clock

Hello,
I am using Daqmx Sample clock function and I am a little confused about the input " rate" of this function.
In Labview Help, this inut is defined as below:
"rate" specifies the sampling rate in samples per channel per second.
Now I set this " rate" to be 8000 and I have 8 channels, Does this mean that the sampling rate of the whole device is 64000? The samples per channel is 1000, what is the buffer size allocated by labview? Is it 8000?
Thanks in advance, I am looking forward to the replies.

Below is another knowledge base article.
http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/dbe7ac32661bcf9b86256ac000682154?OpenDocument
You said that you have eight channels. Are these channels setup in MAX and if so are they global channels or just one Task? Or are you creating a Task in LabVIEW?
If you are reading these channels as a single Task, then each channel is being sampled at "sample rate". Then the buffer size is dependent on "sample mode". If it is continuous then use the chart, but if "Sample Mode" is finite then, NI-DAQmx allocates a buffer equal in size to the value of samples per channel.
When doing finite, "sample rate" is the rate at which the channel will be sampled and "samples per channel" is the number of samples to return. So if sample rate = 1000 and number of samples to return = 100, then 100mSeconds of data will be returned ("number of samples to return/"sample rate"). In other words the channel will be sampled at 1000 until a total of 100 samples has been received.
Chad

Similar Messages

DAQmx Sample Clock (on-board clock) effects

Why would I get slightly different readings when using the Sample Clock (onboard clock) and not using it? On several different cards, I've noticed slightly lower levels of analog input when using the Sample Clock and not using it.
thanks
Richard

Thanks Doug. In LabVIEW, on a SCXI-1102 and a 1502. (DAQ is a PCI-6221).
I understand the benefit of the DAQmx buffer that gets setup when you use Sample Cock, but if I'm just taking "1Chan 1Samp" samples, I wouldn't expect a difference. The sample taken with the Sample Cock included in the Task is a few tenths of a volt less than a the reading taken from a Task not including the Sample Clock (on a ~1V signal).
Message Edited by Broken Arrow on 01-14-2009 04:21 PM
Richard

DAQmx Timing (sample clock).vi

do u know what is the critaria to use DAQmx Timing sample clock.vi... or in what situations this vi must b used?

Hi Pritam,
Thank you for posting on the National Instruments forums.
The DAQmx Timing.VI is used when you need to perform an operation that requries sample timing whether it's Analog Input, Analog Output or Digital IO.
Here is a Developer Zone Article that explains how the Sample Timing VI can be used: Learn 10 Functions in DAQmx and Handle 80% of Your Data Acquisition Applications.
Hopefully this will tell you what you need to know.
Thank You,
Nick F.
Applications Engineer

Wait for Next Sample Clock error, or 'How do I put this VI on a diet'?

Hello!
In the attached VI I've been running since June, I have all the functionality I need. No questions there at all, thanks to much time and help from this board!
My nagging problem is that any time I use the PC for other minor tasks other than Labview, it will display the following error:
209802 occurred at DAQmx Wait For Next Sample Clock.vi:1
A search earlier in the month indicated that it could have been a result of my old and outdated PC; I've since replaced it with a brand-new dell dimension 1100. Celeron 2.53ghz with 1.00gb of ram. Should be enough to service Labview and other minor tasks (automatic antivirus updating and also maintenance tasks). However, any time any other program opens or even if the screen is scrolled around on Labview quickly, I get that same error.
Resource usage when idle, with nothing but this VI running is 5-10%, all labview. Upon scrolling the VI, it quickly jumps to the 58-60% and above mark and soon throws that error.
I know that there's a lot of code here that can be cleaner--I know that even though it's functioning correctly, there could be a less resource-hogging way to go about it. Can anyone give me any suggestions on how to make this VI a little 'lighter'?
Thanks so much in advance,
Ralph
Still confused after 8 years.
Attachments:
Currently Running 063006.vi ‏899 KB

Hi Ralph,
The wait.vi waits until the amount of time has passed. While the wait on next ms.vi uses some kind of quotient and remainder on the computer time until the remainder passed zero.
In this way you can synchronize 2 loops, and somehow it is less time-consuming. The only difference you will see is in the first run!
There you see a smaller amount of time:
Message Edited by TonP on 10-04-2006 04:21 PM
Free Code Capture Tool! Version 2.1.3 with comments, web-upload, back-save and snippets!
Nederlandse LabVIEW user groep www.lvug.nl
My LabVIEW Ideas
LabVIEW, programming like it should be!
Attachments:
Example_BD.png ‏2 KB

Number of samples read is not equal to number of AI Sample Clock pulses - why?

Dear Community,
I am using several PXI-4472s for acquisition and at the same time I am routing the AI Sample Clock signal to a PXI-6608 counter/timer card so that I can time stamp each sample.
Unfortunately I am finding that I always get more AI Sample Clock pulses than samples, so I don't know which time stamp corresponds to which sample. Why is that?
For acquisition I am using something very much like the following DAQmx Sync and Stream example:
Sync and Stream.vi
After stopping the tasks, I use DAQmx Read vi again to read whatever samples might be left in the buffer, but that request always comes back empty. I can't figure out if there are AI Sample Clock pulses at the beginning of the task that don't actually acquire any data, or if I have data left over in the buffer after I stop the task that I am not reading properly.
Any help would be greatly appreciated!
Cas

Cas,
DSA boards (like the 4472) differ from standard DAQ devices. While most DAQ devices use a relatively common type of ADC known as a sequential approximation ADC, a DSA device uses a more specialized ADC known as a Delta-Sigma ADC for its measurements. Delta-Sigma ADCs allow for very precise measurements, and this precision is accomplished by oversampling (frequently 128x or 256x the sampling rate that is being used).
The above is a very brief explanation of the DSA board's inner workings. It is discussed in more detail in the document linked below. If after reading that tutorial, you still have questions, please post back so that this forum can assist you.
Synchronization with Dynamic Signal Acquistion (DSA) Products with DAQmx
Best of luck with your application.
Regards,
Jed R.
Applications Engineer
National Instruments

Using a Counter to error-check External Sample Clock

Hi all,
I am newish to labview and am working on a data acquisition project. I've managed to get the basics under control, but here's my situation and question...
-- I am using the S-6123 card to capture and record data on two or more AI channels. I am using a rotary encoder to generate a pulsetrain that I am using via PFI0 as the sample clock for recording the AI data.
-- This rotary encoder gives 720 pulses per revolution and an index pulse once per revolution.
-- In my data acquisition, I am pulling 1440 samples at a time with the DAQmx "read" function.
I have been experimenting with counters and can get the RPM out of the pulse trains well enough, however I was wondering...
Is there some way to use the 2 counters on the card (and signal routing of the two pulse trains) to double-check that the 1440 samples I take correspond to two exact revolutions, and that I'm not getting ahead of or behind the rotation of the encoder due to missing clock pulses or reading false pulses. I have a couple of ideas on how to attempt to do it, but to me they don't seem very reliable or efficient, so I thought I'd put it to the experts to point out of there is a more obvious way of doing it.
I have attached a pdf of the specifications of the encoder family, the pulses that will be output are on the right hand side of page 2.
With many thanks in advance,
Peter
Message Edited by mumech on 07-22-2008 01:05 AM
Attachments:
REncoder Specs.pdf ‏312 KB

Thanks very much for your reply. I had come across the use of counters with angular encoders but hadn't quite thought of the concept in this way.
I will have to experiment a bit over the next day or to see what this is capable of, the examples seem quite comprehensive, however I'm not sure if I will run into issues due to the fact that I am using the rotary encoder as the sample clock for my analogue data.
Would I indeed be able to compare these values (ideally check the position of the encoder after each set of data acquisition) without a "third party" sample clock common to both? (which isn't appropriate for this application)
If I was only running at low speeds, I might be able to implement this by simply checking the position of the encoder after each read of the data. However, at higher speeds there might be synchronization issues due to the buffering of the analogue data. So when getting the measurement from the encoder counter chances are the analogue data was acquired at an earlier time.
I know I haven't worded this very well, but how might I synchronise this error checking method?

Using an internal sample clock with a digital input

I am using an encoder to measure angle and velocity. The example that I have started with is here. https://decibel.ni.com/content/docs/DOC-6834. The problem I am having is with the Sample clock, I get a timeout at the DAQmx read. If I remove the sample clock the VI runs fine, but I have no idea of my sample rate. Below is the the problem setup with the Sample clock inline.
Attachments:
encoder with timer.JPG ‏50 KB

Hi there, a couple suggestions: first , this is a post that it is suppose to be on the DAQ board. Second, you are not being clear about the error, try to include the error code, description and its location, is it coming out of the channel node or the timing VI? Also what hardware are you using?
Now, If you open the example called "Measure Angular Position.vi" from the NI example finder, drill the DAQmx Create Channel, you will see that you are missing a couple terminals for the task configuration, I wonder if this is part of the error.
Alejandro | Academic Program Engineer | National Instruments

Sharing an external sample clock between PCI-6722 and PCI-6602

I need PCI-6602 work with PCI-6722。6602 shares 6722’s ao/SampleClock as external clock and triggered by 6722’s ao/StartTrigger。The master device is 6722, which refered as Dev1, and the slave device is 6602, which refered as Dev2. A RTSI line is used to connect the two devices correctly.
I use C API to finish my program and my code is as follows:
//config 6722 analog out task
1、DAQmxCreateTask("NI6672", &hAOTask);
2、DAQmxCreateAOVoltageChan(hAOTask, "Dev1/ao0", "", -10.0, 10.0, DAQmx_Val_Volts, "" );
3、DAQmxCfgSampClkTiming(hAOTask, "", 1000.0, DAQmx_Val_Rising, DAQmx_Val_ContSamps, 1000);
4、DAQmxWriteAnalogF64(hAOTask, 1000, 0, 10.0, DAQmx_Val_GroupByChannel, data, NULL, NULL);
//config 6602 counter task
5、DAQmxCreateTask("NI6602", &hCounterTask);
6、DAQmxCreateCICountEdgesChan(hCounterTask, "Dev2/ctr0", "", DAQmx_Val_Rising, 0, DAQmx_Val_CountUp);
//use /Dev1/ao/SampleClock for external clock
7、DAQmxCfgSampClkTiming(hCounterTask, "/Dev1/ao/SampleClock", 1000.0, DAQmx_Val_Rising, DAQmx_Val_ContSamps, 1000);
//use /Dev1/ao/StartTrigger
8、DAQmxSetTrigAttribute (hCounterTask, DAQmx_ArmStartTrig_Type, DAQmx_Val_DigEdge);
9、DAQmxSetTrigAttribute (hCounterTask, DAQmx_DigEdge_ArmStartTrig_Src, "/Dev1/ao/StartTrigger");
10、DAQmxSetTrigAttribute (hCounterTask, DAQmx_DigEdge_ArmStartTrig_Edge, DAQmx_Val_Rising);
//start counter task first
11、DAQmxStartTask(hCounterTask);
//start 6722 task
12、DAQmxStartTask(hAOTask);
I run it on the MAX virtual Device, and the Step 11always returned -89120。
I try to slove this problem, so I change the Step 7, use /Dev2/PFI9 to instead of /Dev1/ao/SampleClock.
7、DAQmxCfgSampClkTiming(hCounterTask, "/Dev2/PFI9", 1000.0, DAQmx_Val_Rising, DAQmx_Val_ContSamps, 1000);
The code runs well, but I don’t know which terminal is connected by /Dev2/PFI9. Does it connect to /Dev1/ao/SampleClock？
I use another API DAQmxConnectTerms to ensure that, I add a Step before Step 11.
DAQmxConnectTerms( "/Dev1/ao/SampleClock", "/Dev2/PFI9", DAQmx_Val_DoNotInvertPolarity );
The program also run well. But I am still not sure that 6602 is sharing /Dev1/ao/SampleClock。If not, which terminal of Dev1 is connected by /Dev2/PFI9?
Is my code right? If not, hwo to fix my code or supply some example for me? Thanks.

Hello Shokey,
From looking over your post, it looks like you want to program in C, using simulated instruments, a master/slave design with a PCI-6602 and PCI-6722. The PCI-6722 is the master device and the PCI-6602 is the slave device. In order to implement this with the real cards, you would need a RTSI cable between the 2 cards in order to pass the triggers and the sample clock. Unfortunately with simulated devices you can't implement this so parts of your code won't be able to work exactly like if you had the instrument.
If you did have the instrument, you can implement this by performing the following steps:
Master Device:
1.) Export the ao/SampleClock and ao/StartTrigger to a RTSI Line. (See DAQmx C Reference help for DAQmxExportSignal to export these)
Slave Device:
1.) Set the Sample clock and the trigger to the RTSI.
There is another forum that I think will help you out to implement this correctly. In this forum, the customer was trying to export a trigger through a RTSI and the problem he was experiencing was a broken RTSI cable. His code, he states, works. I hope this helps you with this and if you have any more questions, feel free to post.
Jim St
National Instruments
RF Product Support Engineer

Err. -200303: External sample clock source...

Dear Readers
I'm using Ni-DAQmx 8 and have a PCIe-6259 card.
I wrote the following code (in VC++ 6).
int main(int argc, char* argv[])
    int32       error=0;
    TaskHandle taskHandle=0;
    uInt8      data[10]={1,2,4,8,16,32,64,128,256,0xFFFFFFFF};
    char        errBuff[2048]={'\0'};
    (error = DAQmxCreateTask("",&taskHandle));
    (error = DAQmxCreateDOChan(taskHandle,"Dev1/port0","",DAQmx_Val_ChanForAllLines));
    (error = DAQmxCfgSampClkTiming(taskHandle,NULL,1000.0,DAQmx_Val_Rising,DAQmx_Val_ContSamps,1000));
    error = DAQmxWriteRaw(taskHandle, 10, true, 10.0, data, NULL, NULL);
        if( DAQmxFailed(error) )
        DAQmxGetExtendedErrorInfo(errBuff,2048);
    ERROR: -200303: External sample clock source must be specified for this application
    error = DAQmxStartTask(taskHandle);
I See no output on the oscilloscope.
I tried to put in several values for ClockSource in DAQmxCfgSampClkTiming like Dev1/PFI0, .... - but it never worked.
Could anyone please help me?
Thanks...
Pascal

Hi Robert
Do yo mean something like this:
int main(int argc, char* argv[])
    int32       error=0;
    TaskHandle digiTaskHandle = 0;
    TaskHandle aiTaskHandle = 0;
    uInt32      data[10]={0xFFFFFFFF,2,4,8,16,32,64,128,256,0xFFFFFFFF};
    float64        dummyBuffer[10];
    char        errBuff[4096]={'\0'};
    error = DAQmxCreateTask("",&digiTaskHandle);
    error = DAQmxCreateTask("",&aiTaskHandle);
    error = DAQmxCreateDOChan(digiTaskHandle,"Dev1/port0","",DAQmx_Val_ChanForAllLines);
    error = DAQmxCreateAIVoltageChan(aiTaskHandle, "Dev1/ai0", "", DAQmx_Val_RSE, -5.0, 5.0, DAQmx_Val_Volts, "");
    error = DAQmxCfgSampClkTiming(aiTaskHandle, "/Dev1/ai/SampleClock", 1000.0, DAQmx_Val_Rising, DAQmx_Val_ContSamps, 1000);
    error = DAQmxCfgSampClkTiming(digiTaskHandle,"/Dev1/ai/SampleClock" ,1000.0,DAQmx_Val_Rising,DAQmx_Val_ContSamps,1000);
    error = DAQmxStartTask(aiTaskHandle);
ERROR:
"An attempt has been made to perform a route when the source and the destination are the same terminal.
In many cases, such as when configuring an external clock or a counter source, you must select a PFI, PXI Trigger, or RTSI line as the sou"
//    error = DAQmxReadAnalogF64(aiTaskHandle, 10, 20.0, DAQmx_Val_GroupByChannel, dummyBuffer, 10, NULL, NULL);
    if( DAQmxFailed(error) )
      DAQmxGetExtendedErrorInfo(errBuff,4096);
    error = DAQmxWriteRaw(digiTaskHandle, 10, true, 10.0, data, NULL, NULL);
    //error = DAQmxStartTask(aiTaskHandle);
    if( DAQmxFailed(error) )
      DAQmxGetExtendedErrorInfo(errBuff,2048);
    return 0;
Could you please explain me how to do it right?
Pascal

Selecting sample clock frequency for NI 4472

HelIo:
I have been using NI 4472 DSA on a PCI slot for reading accelerations. I was reading the NI 4472 User Manual and under "Selecting your sample clock frequency", it specify two increments (95.37 uS/s for Fs<51.2 kS/s and 190.7 uS/s for Fs>51.2 kS/s). Can you explain what these increments mean? I understand the sampling frequency, but what does this time increment mean?
Also, it says "If you do not specify a rate at a multiple of the increment, NI-DAQ will automatically choose the next higher step for you". Dose that mean I cannot specify any random value for Fs? Dose it have to be a certain multiplication. Please explain this for a novice to Labview/DAQ.
Thanks a lot in advance.

Hello MiamiVipul,
Those statements in the User Manual mean that the PCI-4472 only has a finite set of sample rates that it can produce. The allowable sample rates are given by 51.2 kS/s - k * 95.37 uS/s or 51.2 kS/s + k * 190.7 uS/s, where k is an integer. As you can see, the step size is quite small, so you still have a lot of flexibility.
As an example, if you specify a sample rate of exactly 51.2 kS/s, that would be fine. However, if you try to set the sample rate to something between 51,200 S/s and 51,199.990463 S/s (51.2 kS/s - 95.37 uS/s), the driver will automatically coerce that sample rate to next highest allowable rate, or 51.2 kS/s. In order to find out the exact value that the driver is using, you can read the from the DAQmx Timing Property "Sample Clock:Rate" as shown below:
I hope this helps!
Best regards,
Message Edited by Jarrod B. on 01-04-2007 09:03 AM
Attachments:
ReadSampleRate.JPG ‏6 KB

PCI-6229 Digital I/O sample clock problem

Hi,
I am using PCI-6229. I need to use digital output channel to generate 20KHz 30%duty cycle pulses.
The datasheet shows DO sample clock frequency can be 1M Hz. But in may application, only 100KHzTimebase can work to generate. But acctually I need at least 200K Hz.
Attached is the Vi I made. Can anyone help me with this problem?
Thanks
Solved!
Go to Solution.
Attachments:
Digital pulse_DO Channel.vi ‏26 KB

Hello All,
I tried to modify the VI posted in this thread in order to aquire a digital signal with the PCI-6229. Sinc the frequency of the signal is below 1k i tried to devide the signal of ctr0 respectively of freqout by 8 or 16 since 6.25k or 12.5k sampling frequency would be more than enough for my purpose. By the way, when I am using the 100k timebase for the timing of the task the programm is working. Since i try to monitor up to 20 channels, the amount of data genereated is too much. Therefore I tried to use the modified VI.
Sometimes, the VI works, but almost always, the DAQmx - Read VI doesn´t terminate.
Has anybody an idea what i did wrong?
Thank you for your assistance.
Sincerely,
Mirko
Attachments:
Digital pulse_DI Channel-1_mod.vi ‏32 KB

Unable to use sample clock digital filter - PCI6602

I can't seem to get digital filtering of the sample clock to work on my PCI6602. I'm using DAQmx 7.4, with one of the counters configured for buffered-edge counting. Whenever I try to configure digital filtering on the sample clock (coming in on pfi10):
counterTask.Timing.SampleClockDigitalFilterEnable = true;
counterTask.Timing.SampleClockDigitalFilterMinimumPulseWidth = 0.000005;
I get the following error message when I start the task:
Additional information: Digital filtering is not available for the given terminal.
Device: Dev3
Property: NationalInstruments.DAQmx.Timing.SampleClockSource
Corresponding Value: /dev3/pfi10
Channel Name: phaseLockOscillator
Task Name: PhaseLock task
Status Code: -200772
I thought digital filtering was supported on all pfi inputs on the 6602 - so can anybody give me a hint as to what I'm doing wrong !?
Many thanks in advance,
Jony Hudson

I have the same problem with the PCI-6280., help me please!

Accessing the Sample Clock

I wish to use the sample clock of my E-Series board to establish a time base (which will have greater resolution than LabViews standard millisecond timers).
How can I do this?
Also, do I have to be acquiring data in order to use the clock? Or, can I still access the clock to use as a counter even when I'm not taking data?
BC

Hi,
You can use the "timed loop" functionality in LabVIEW 7.1 to use your E-series card's timing to control your software.
Check out this example:
http://venus.ni.com/stage/we/niepd_web_display.DISPLAY_EPD4?p_answer=&p_guid=EDFBFDB844C96972E0340003BA7CCD71&p_node=%20201207&p_rank=&p_source=External&p_submitted=N
You basically set up a while loop that uses a DAQmx Task to perform timing.
-Sal

9188 sample clock for Example VI

Hi,
I'm trying to run the Example VI: "Gen Event for Ext Signal" on Labview 10 with the NI cDAQ 9188. I'm getting an error (see below). I tried fixing this error by changing the code from "Hardware Timed Signal Point" to "Continuous" but then it seems my sample clock doesnt work. Any ideas what's going on?
>>>>>>>>
Error -200077 occurred at Property Node DAQmx Timing (arg 3) in DAQmx Timing (Sample Clock).vi:2->Gen Event for Ext Signal.vi
Possible reason(s):
Requested value is not a supported value for this property. The property value may be invalid because it conflicts with another property.
Property: SampQuant.SampMode
Requested Value: Hardware Timed Single Point
You Can Select: Finite Samples, Continuous Samples
Task Name: _unnamedTask<296B>
>>>>>>>>>>

Hi there roto,
Does the following link help?
NI-DAQmx Hardware-Timed Single Point Support for Oversample Clock Timed Devices: http://zone.ni.com/devzone/cda/pub/p/id/1325
Best,
Ryan C.
Applications Engineer
National Instruments

672PCI 6723 error when attempting to generate DO signal with 20kHz sample clock

I have a piece of code that successfully worked on the PCI-6224 card, but when I tried to implement the same code on the PCI-6723 card I have run into problems.
Here is the code that I am using:
ManchConversion6723();//produces SendIt array of series of 1s/0s
// DAQmx Configure Clock
DAQmxErrChk (DAQmxCreateTask("",&taskHandleFRQ));
DAQmxErrChk (DAQmxCreateCOPulseChanFreq(taskHandleFRQ,"Dev3/ctr0","",DAQmx_Val_Hz,DAQmx_Val_Low,0,20000,0.5));
DAQmxErrChk (DAQmxCfgImplicitTiming(taskHandleFRQ,DAQmx_Val_ContSamps,72));
// DAQmx Configure Digital Output
DAQmxErrChk (DAQmxCreateTask("",&taskHandle));MessageBox("D");//vj
DAQmxErrChk (DAQmxCreateDOChan(taskHandle,"Dev3/port0/line0","",DAQmx_Val_ChanPerLine));MessageBox("E");//vj
DAQmxErrChk (DAQmxCfgSampClkTiming(taskHandle,"/Dev3/Ctr0InternalOutput",20000,DAQmx_Val_Rising,DAQmx_Val_ContSamps,72));
// DAQmx Write Code
DAQmxErrChk (DAQmxWriteDigitalLines(taskHandle,72,0,10.0,DAQmx_Val_GroupByChannel,SendIt6723,NULL,NULL));
// DAQmx Start Code
DAQmxErrChk (DAQmxStartTask(taskHandleFRQ));
DAQmxErrChk (DAQmxStartTask(taskHandle));
When I arrive at the DAQmxCfgSampClkTiming line, I receive an error stating:
DAQmx Error: Measurements: Requested value is not a supported value for this property.
PropertyAQmx_SampTimingType
You Have Requested: DAQmx_Val_SampClk
You Can Select: DAQmx_Val_OnDemand
Task Name: _unnamedTask<0>
Status Code: -200077
I believe the problem stems from the source variable of the function. I am simply tring to send the data out at the 20KHz rate.
Any help would be greatly appreciated. Thanks in advance!
Solved!
Go to Solution.

Nevermind. Seems as though the PCI-6723 does not contain correlated DIO channels. In other words, sample clocks can not be tied to the DIO channels to allow for digital waveform generation. According to the AO Series User Manual, this applies to NI 6731/6733 Only. The error was trying to tell me that only a single transmit or receive channel was allowed.
For this reason, I will just stick with my PCI-6224 card.
Sorry for the confusion.

Daqmx Sample clock

Similar Messages

Maybe you are looking for