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Simultaneous sweep and acquire

Can I simultaneously use Sweep to vary the frequency of a sine wave sent out ao0 while I am acquiring on ai0?
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Message 1 of 12
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I talked to an NI rep and he told me this can't be done. I'd need the full LabVIEW for that.
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Hello Steve,

Thanks for posting. I was just going to post and tell you the same thing after running some tests in Signal Express, and then my window updated and I saw you had already found the answer. While Signal Express is very user friendly, it works solely with Express VIs, which means for advanced functionality like what you described you will need to work with the lower level VIs available in LabVIEW. Do you have any further questions I could help you with?

Regards,

Mallori M.

Mallori M
National Instruments
Sr Group Manager, Education Services

ni.com/training
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Thanks for your reply, Mallori. I've got SignalExpress doing what I need for now.
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Hi SSteve,

 

I'd like to correct the earlier reply from Mallori about Simultaneous Sweep and Acquire using SignalExpress. It's definitely possible to perform simultaneous sweep and acquire using SignalExpress. The only limitation being very high frequencies and certain hardware (cDAQ for example).  

 

1) N Sample Simultaneous Sweep and Acquire

 

The following figure shows the set up to simultaneously sweep and acquire N Samples. The voltage sweeps from 1 to 4 V in 6 iterations. (Note: To view the Sweep Output array as follows, you will have to ignore time stamps i.e. Right click Display >> Time Stamp >Ignore)

 

 

The key for this to work is the way the DAQmx Acquire (Analog Input) step is set up. Apart from selecting the Timing Settings (Acquisition Mode, Samples to Read and Rate) to match the DAQmx Generate (Analog Output) step; the Start Trigger should be set to the trigger on the Analog Output rather than <none>. Choosing a Start Trigger type would conflict with the Execution Control which has to be disabled

 

The attached zip file (SignalExpressSweepExamples.zip) has an N Sample Sweep SignalExpress 3.0 Project (Sweep_NSamples.seproj)

 

2) Continuous Sweep and Acquire

 

For the Continuous Sweep and Acquire Case, I've chosen to sweep the frequency rather than the voltage (to showcase another type).

 

 

I've changed the DAQmx Generation and Acquire steps to be continuous and also shared the clocks between Analog Input and Output.  Also, to ensure continuous generation of the signal, choose N Periods (in the Create Analog Signal Step), which will force the number of periods in the signal to be an integer.

 

The attached zip file (SignalExpressSweepExamples.zip) has a Continuous Sweep SignalExpress 3.0 Project (Sweep_Continuous.seproj)

 

 

 

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Message 5 of 12
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The pictures didn't show up earlier, hence I'm reposting

 

Hi SSteve,

 

I'd like to correct the earlier reply from Mallori about Simultaneous Sweep and Acquire using SignalExpress. It's definitely possible to perform simultaneous sweep and acquire using SignalExpress. The only limitation being very high frequencies and certain hardware (cDAQ for example).  

 

1) N Sample Simultaneous Sweep and Acquire

 

The following figure shows the set up to simultaneously sweep and acquire N Samples. The voltage sweeps from 1 to 4 V in 6 iterations. (Note: To view the Sweep Output array as follows, you will have to ignore time stamps i.e. Right click Display >> Time Stamp >Ignore)

 

 

The key for this to work is the way the DAQmx Acquire (Analog Input) step is set up. Apart from selecting the Timing Settings (Acquisition Mode, Samples to Read and Rate) to match the DAQmx Generate (Analog Output) step; the Start Trigger should be set to the trigger on the Analog Output rather than <none>. Choosing a Start Trigger type would conflict with the Execution Control which has to be disabled

 

The attached zip file (SignalExpressSweepExamples.zip) has an N Sample Sweep SignalExpress 3.0 Project (Sweep_NSamples.seproj)

 

2) Continuous Sweep and Acquire

 

For the Continuous Sweep and Acquire Case, I've chosen to sweep the frequency rather than the voltage (to showcase another type).

 

 

I've changed the DAQmx Generation and Acquire steps to be continuous and also shared the clocks between Analog Input and Output.  Also, to ensure continuous generation of the signal, choose N Periods (in the Create Analog Signal Step), which will force the number of periods in the signal to be an integer.

 

The attached zip file (SignalExpressSweepExamples.zip) has a Continuous Sweep SignalExpress 3.0 Project (Sweep_Continuous.seproj)

 

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Message 6 of 12
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Hi Nitin,

Thanks for the explanation. You learn something new every day! 🙂

Regards,

Mallori M.

Mallori M
National Instruments
Sr Group Manager, Education Services

ni.com/training
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Message 7 of 12
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Hello, 
 
I have a very similar issue and I am also a very begginer with LV and signal express. I am trying to generate a signal consisting of a ramped signal and a sine (summed up). I have to generate a signal, pass it to the old analog potentiostat and acquire response of the system (its an electrochemical cell) .I decided to generate the signal using Create Analog Signal and a formula signal (formula signal - =a*sin(w*t)+t). I pass the generated signal to the DAQmx (I have a virtual/simulated 6052e card insalled). I try to set a DAQmx acquire signal to simultaneously acquire response by setting the trigger to myDev1/ao0  and timing to ao0 too. I want the sampling to be continuous. I have to use a sweep however generating such a nice ramped sine seems to be harder than with a formula signal.
 
I set sine frequency to 1Hz, amp 0.1V, sample rate 1k, Block size to10k, so signal lasts for 10s. However my acquisition DAQmx does not acquire the signal continuously and it lasts for only 100ms.  I have attached my file. 
 
Regards, Michal

 

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Message 8 of 12
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Hi wrogu,

 

Have you tried this with the actual 6502e device?  It may be something to do with the simulation.  Additionally, this is an old thread (2008).  You may have more people available to help if you start a new thread and ask your questions there.  Let me know how things go.

| Zach J. | Systems Engineer, HIL and Test Cells | National Instruments |
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Message 9 of 12
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Hi

 

Sadly, this is just another question on the same topic. 

 

I have used the Signal express examples/tutorials for sweeps and try to modify them to match my equipment, but I am facing multiple problems:

 

I am using

 

PXIe-1073 chassis

PXIe-4464 card

PXI-4461 card

 

and SIGNAL EXPRESS.

 

I have configured the task to sweep in frequency, linearly 50-450 Hz, and 10 points (Do these points inply that the sweep is not really a sweep but that its a collection of signals of a median interpolated frequency beeing played one after the other?).

I have configured my Create Analogue signal to have 44.1k S/s, and my block size to be 882 S.

My starting frequency is 50 Hz. I have tried sine or Formula with equal results.

I have configured my DAQmx generate analogue output to be PXI_Slot5_4461_ao0.

I am also acquiring sound pressure via 2 TED equipped mics and 1 direct voltage line using the PXIe-4464 card on slot 2.

 

All should be triggered via PFI 0 on the PXI-4461 card with an external trigger, that I am also picking up with card PXIe-4464 for reference.

 

My problems are:

 

The generated signal: played through an amp and a compression driver sounds like a collection of  frequency varying blocks which are not crossfaded and clip, exactly the amount of times I have chosen as points in the sweep.

I have chosen the block size to be exactly 1 wavelength at the base frequency hoping that this would solve the crossfading problem but it hasnt.

 

There are other multiple problems with the acquisition side of things, and trigger definition, but for now I would like to solve this signal generation problem.

 

Thanks.

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