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Real-Time Measurement and Control
real time
Thomaz,
In general this is possible, so we will need to know more about your specific application to make recommendations. If you look at the attached VI (LV 7.0) we can plot a circle with 1000 points at about 50 Hz (running on a 866 MHZ P2).
Could you provide more information about your application? What version of LV are you using? LV or LV RT? If LV RT, how are your transferring the data from your RT system back to your host for visualization? What information do the two sensors represent? How do you convert this data to represent the circle on your user interface? How many samples from your sensor do you need to update the plot?
Christian L
NI Consulting Services
In general this is possible, so we will need to know more about your specific application to make recommendations. If you look at the attached VI (LV 7.0) we can plot a circle with 1000 points at about 50 Hz (running on a 866 MHZ P2).
Could you provide more information about your application? What version of LV are you using? LV or LV RT? If LV RT, how are your transferring the data from your RT system back to your host for visualization? What information do the two sensors represent? How do you convert this data to represent the circle on your user interface? How many samples from your sensor do you need to update the plot?
Christian L
NI Consulting Services
Can you be more specific about how you convert the (368) data points into the location of the rotor? Do you calculate one averaged position of the rotor per rotation, or per second, or more frequently. What is the typical frequency of the vibration (displacement of the rotor) that you are plotting?
In an ideal situation without vibration would the air gap for each of the two sensors stay constant? If so then the measure of the air gap is a direct measurement of the displacement of the rotor in the X and Y dimension and you should be able to plot this on your graph at the rate supported by the graph.
In your current implementation, do you know what causes the VI to only plot every 7 seconds?
Christian
In an ideal situation without vibration would the air gap for each of the two sensors stay constant? If so then the measure of the air gap is a direct measurement of the displacement of the rotor in the X and Y dimension and you should be able to plot this on your graph at the rate supported by the graph.
In your current implementation, do you know what causes the VI to only plot every 7 seconds?
Christian
Hello Thomaz,
Please also see Preston's comments. I talked with him about your application and the order analysis toolkit may be very helpful for you in your application as you move forward.
Looking at your code, the main problem lies with the data acquisition. In your code you use the single point acquisition function AI Sample Channel which includes no timing control. You repeat this function 368 times in the For Loop, but you don't know how fast the loop is running and therefore how fast the samples are being acquired. The 1 ms delay outside the For Loop has no effect on the timing of the For Loop and the timing of your data acquisition.
Instead of the single point functions, you should use the AI Acquir
e Waveforms VI to acquire a set number of samples (368) at a set rate (1000 Hz) from both channels. In this case the timing will be handled by the data acquisition card so that you know that interval between samples is 1 ms. This function will return an array containing all the data points which you can then process using the array manipulation and arithmetic functions. If you plot the raw data from each of the channels on a waveform graph you will likely see a somewhat sinusoidal pattern like the plots on the graphic that Preston showed.
I tried making the changes in LV 7.0 and then saving the VI back to 6.1. Please see attached. The DAQ VI will likely not load/show in 6.1 and you will need to replace it after opening the attached VI.
If you make this change, you will still have a limitation that you don't know where in a revolution of the rotor you start sampling the data. So repeated acquisition sequences will not match each other in regards to this phase offset. Eventually yo
u will want to use a continuous data acquisition operation where the data is acquired without breaks and processed and plotted at the same time.
Christian
Please also see Preston's comments. I talked with him about your application and the order analysis toolkit may be very helpful for you in your application as you move forward.
Looking at your code, the main problem lies with the data acquisition. In your code you use the single point acquisition function AI Sample Channel which includes no timing control. You repeat this function 368 times in the For Loop, but you don't know how fast the loop is running and therefore how fast the samples are being acquired. The 1 ms delay outside the For Loop has no effect on the timing of the For Loop and the timing of your data acquisition.
Instead of the single point functions, you should use the AI Acquir
e Waveforms VI to acquire a set number of samples (368) at a set rate (1000 Hz) from both channels. In this case the timing will be handled by the data acquisition card so that you know that interval between samples is 1 ms. This function will return an array containing all the data points which you can then process using the array manipulation and arithmetic functions. If you plot the raw data from each of the channels on a waveform graph you will likely see a somewhat sinusoidal pattern like the plots on the graphic that Preston showed.
I tried making the changes in LV 7.0 and then saving the VI back to 6.1. Please see attached. The DAQ VI will likely not load/show in 6.1 and you will need to replace it after opening the attached VI.
If you make this change, you will still have a limitation that you don't know where in a revolution of the rotor you start sampling the data. So repeated acquisition sequences will not match each other in regards to this phase offset. Eventually yo
u will want to use a continuous data acquisition operation where the data is acquired without breaks and processed and plotted at the same time.
Christian
