In order to sample a 3 Hz sine wave, I have to scan it at 30 Hz.

My setup is as follows:
I have two PXI 6031E DAQ cards in a PXI 1000B chassis. Each DAQ card connects to a SCXI 1001 chassis. On the first SCXI chassis I have six SCXI 1102C modules and in the second SCXI chassis I have three SCXI 1102 modules. I set up two seperate scan lists. One for the first DAQ card and one for the second DAQ card. The actual scanning functions are placed in seperate threads. After I acquire the data, I move it to "shared memory." The display program reads the value from shared memory and plots the value. For simplicity I left the data as a short int and plotted it that way. If I connect a function generator to any channel I can read a clean wave only if my scan rate is 10
times the function generator value. For example, if I want to read a 3Hz sine wave I have to set the scan rate on the DataAcq program to 30Hz and the update rate on the display program to 30Hz. Should I be able to read a 3Hz sine wave while scanning at 3Hz? Also, I am open to any recommendations in my code.
Attachments:
DataAcq.zip ‏6 KB
Display.zip ‏5 KB

What you have discovered is quite normal for acquiring data in the time domain. If you were only interested in the frequency domain, you could follow the Nyquist criteria and sample at a frequency at least twice your desired frequency (6 Hz). Since you wish to examine the data as a sine wave (to view and recognize), you need to sample the waveform at a rate of at least ten times the desired frequency. Hence, to plot and recognize a 3 Hz signal, you would need to sample at a rate of 30 Hz. This action allows ten actual data points per wave cycle.
As a rule, I use 16 times "oversampling" for my application where I desire to manipulate the data in the time domain. Twenty times oversampling would be even better. It really depends upon the resolution you would like to
see in your data.

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Help Creating a Sine Wave in Numbers '09?

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theleonhearted wrote:
The instructions say to make a new column in column D and enter in the equation 1.435x-2501.1, which is derived from the linear fit treadline equation I had calculated earlier. After that I am to copy it down to match the number of cells in column A (626), which I did, so now every cell in D down to 626 contains that equation above.
I'm not sure of the reason for this step.
1.435x-2501.1
Entered into D2, with the x value in A2 is expressed as:
=1.435*A-2501.1
which is part of the formula below.
Then, I enter 1 in cell E1 and 1/12 in order to arbitrarily guess at the sine wave amplitude and period, respectively, and finally I then select cell D1 and put in this equation:
=1.435*A2-2501.1+($E$1*SIN(A2/$F$1))
I'm assuming "1/12" goes in F1.
I've also assumed row 1 is a Header row, and have entered your formula into the first data row (D2)
Your formula is now:
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or
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You haven't given any specifics regarding the raw data, so I've arbitrarily set it to a positive linear slope by making A =ROW()-1.
After that I grab cell D2, drag it down to select all the cells in column D, and add it to the graph by (I think) dragging it onto the graph, as Numbers says to do. What I'm uncertain of is where to go from here. Here are the instructions:
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Select Column A: Click on any cell to make the table active show the row and column Reference tabs.
Click on column A's reference tab.
Command-clickon column D's reference tab to add it to the selection.
Click the Chart button in the tools and choose the Scatter chart icon from the menu.
If I've read this correctly, your formula imposes a sine wave onto the set of data.
Here are the results. The expanded chart at the right shows the approximately the area bounded by the light blue rectangle at the upper end of the plot in the larger chart.
Regards,
Barry

How to take a derivative of a sine wave?

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Solved!
Go to Solution.

Just speculating, but...
The derivative of a 10 Hz sine wave should have an amplitude of about ±60 (2*pi*10).
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Coincidence?
Best Regards,
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Phase Difference.vi ‏22 KB

How to get the sine wave sample of the input and output in the same time?

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Attachments:
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Hello Yun_Zhu,
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Sampling sine wave and saving the samples in an array.

helo..
I am new to Labview and i need some help regarding sampling the sine wave.
I have generated the sinewave in labview and now i want to sample it.(do i need an ADC for sampling?) and the samples should be saved in an array.
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Thanks in advance

All of the functions that generate a sine wave in software do save all of the samples in an array. You just need to know how to get them. Since you did not mention the function you used to create the sine wave, lets assume it's the Express VI Simulate Signal. On the signal output, wire a Convert From Dynamic Data type function and select the default 1d Array of Scalars. Right click on the output of this and select Create Indicator. You now have the array. If you are using Sine Waveform which outputs a waveform data type, just wire up a Get Waveform Components function and select the item 'Y'.
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Message Edited by Dennis Knutson on 10-28-2008 08:23 PM
Attachments:
Get Y Array.PNG ‏4 KB

Sampling a sine wave

Hi everyone
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http://www.ni.com/white-paper/3016/en/
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http://www.ni.com/tutorial/3116/en/
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Sampling sine wave in labview

how to read the corresponding voltage value for each point on sine wave(each sample)?
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continued here....
LabVIEW Champion . Do more with less code and in less time .

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Is this a labview problem, or
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Ben Rayner
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www.DSAutomation.com
Ben Rayner
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Dear all,
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Attachments:
64 Channel Programmatic v2.vi ‏22 KB

Hi Zhuming,
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My Sine Wave File sounds different in Logic than iTunes

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Message was edited by: Imol

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- tbob
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PXI-board only returns perfect sine wave

Hi, everyone!
This is a strange one:
Im peforming synchronized sampling from two boards; one is a PCI-6224 in my computer and the other a PXI-6229 located in our PXI-system. Being a rookie when it comes to labview, I was quite proud of myself for managing this all by myself. However, when i looked closer at a 10 sec test-record I noticed something peculiar. Although none of the 32 (differential) channels had inputs during the recording, the PXI-board returned 16 perfect 1 Hz sine waves with exactly the same amplitude as the measurement range. Attaching a signal to the terminal block didn't alter this. The PCI-board returns only weak 50 Hz (power network) noise, as expected. What is going on ??
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regards, Einar

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Generating a 6X Sine Wave using an absolute encoder

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Now the long version of the problem. I have a 9-bit absolute encoder connected to a motor shaft (up to 420Hz). From the encoders 9-bit (0-511) parallel signal I need to create a synchronized 6X sine wave (up to 2500Hzwith an adjustable phase relation. Picture an electronic timing chain. For every cycle of the encoder, I need to produce six full sine wave cycles with a variable tuned phase shift. I have LabView 7 w/RT.
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Phil,
Another different option to solve your application would be to use the new LabVIEW FPGA module and the 7831R reconfigurable I/O hardware. Using these tools you can configure the FPGA on the board to generate the sine wave based on the 9-bit parallel input. The most simple setup would be to have a lookup table in the FPGA that has a corresponding output value to each of the 512 possible input values. This 512 sample table would contain 6 cycles of a sine wave. Every time the parallel input changes the analog output value would be updated accordingly from the lookup table. This setup would also allow to easily add a phas
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Christian L
NICS
Christian Loew, CLA
Principal Systems Engineer, National Instruments
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In order to sample a 3 Hz sine wave, I have to scan it at 30 Hz.

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