RMS calculation in Statistics Express

Hi all,
I want to figure out whether the RMS calculation in Statitics Express will output a signal with a different "number of samples" than the raw signal. I read about the following knowledgebase:
http://digital.ni.com/public.nsf/allkb/862567530005F09C862567210074EA10
but still not quite sure if averaging will reduce the number of samples. Can anyone help me out?
Thanks in advance for any answers!

It is getting away from the Express VIs, but you could use the RMS PtByPt VI inside of a FOR loop. Then it is a question of how large of an RMS window do you want. Same idea as a moving average.
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Statistics Express VI - help

Under the help option in the statistica express VI this is given to explain the time between samples (dt)
Time between samples (dt)
—Bases the calculation on the time between samples in
Signals
My design is two micophones and one sound and finding the time delay between the two.
Now does this mean it takes the difference from when one signal starts and the other starts
(say when microphone 1 first picks up a signal and then microphone 2)
Or does it show the time difference between the two signals ?
(as in the delay between the samples)
I'll attach the VI's below to see it that helps makes sense
Solved!
Go to Solution.
Attachments:
VI.zip ‏980 KB

dt is the time spacing between sampled points. In your case, dt=0.001.
If you convert to plain 1D arrays, the sampling information is lost, meaning the cross correlation in in units of the array indices. Given dt, you can calculate the the spacing in seconds from the spacing in index units.
You can also set the dt of the x-axes of the graphs so the display is in seconds.
LabVIEW Champion . Do more with less code and in less time .

How do I setup an RMS Vi to just do a RMS calculation on just a specified part of the waveform?

I want use an RMS vi to calculate the RMS value of an incoming waveform. I only want to do this calculation on a specified part of the wave form, so it can be used to create a beam pattern for a sonar transducer. Can anybody out there help me with this problem. For instance I would like to do the RMS calculation 1.5ms to 1.7ms

You can extract the part of interest of your waveform before calculating the RMS value. Use the Waveform tool VI called Get Waveform Subset.vi located in the Waveform Operations palette. In your case input Start = 1.5 ms, Duration = 0.2 ms and make sure the Mode parameter is set = Relative Time.

How do I get the statistics express to read more than 10 segments when reading from a .lvm

I have tried 2 ways of doing this. I had an for loop set up with a "Read labVIEW Measurement FIle" then a xy chart to plot the 2 measurements vs. each other. The chart works and will plot everything great but the "Statistics" express will only take 10 samples at a time and will keep redoing the statistics for each subsequent segment of 10 samples. I tried to change this to a while loop but then the same thing happens with the stats and the xy chart does not graph. How do I get the stats calculate for the entire file?

Richard,
Thank you for contacting National Instruments. I think I understand what you are looking to do here, but it might be easiest for myself and others to help you more specifically if you post a screenshot of your code, or your actual VI. However, I looked into trying to achieve something similar, and used a loop structure to bring the information in from a file. Then, outside the loop, I used the Statistics Express VI from the Mathematics palette to obtain some statistical values. What type of statistics are you looking to receive from this program?
Jason W.
National Instruments
Applications Engineer

Statistics Express Kurtosis inconistency Labview 2011 (Bug 215683)

Hi All,
I am currently working with a data collection program from which I need to output the skew and kurtosis values for an array of 30 data points. As I was already using the Statistics Express VI to calculate mean, s.d. etc. I just added the skew and kurtosis outputs to that VI. I then set up a basic VI to generate a 1D array of random numbers to let me compare the Express VI to the skew and kurtosis VI on the mathematics > probability and stats. palette.
The skew and kurtosis values are inconsistent between the two VIs. If I calculate the skew and kurtosis by hand I can see that the non-express VI appears to be giving the correct answer. I did some digging and found that this has been labelled as bug no. 215683 and is described as having been fixed as part of Labview 2011. I am running Labview 2011 with SP1 so I'm not quite sure why the two VIs are still inconsistent.
I realise that I can simply use the VI which is giving the correct answer but I am curious as to why a bug which should be fixed still appears to be active in my version of Labview.
Any thoughts/ input would be greatly appreciated.
Many thanks in advance

Hi cat,
why don't you get rid of that buggy (as it seems) ExpressVI?
The remaining data (StDev, variance) are provided by just another function from math->statistics palette…
You can also opne the ExpressVI to see, how it calculates those data and why it does produce different results!
Best regards,
GerdW
CLAD, using 2009SP1 + LV2011SP1 + LV2014SP1 on WinXP+Win7+cRIO
Kudos are welcome

Statistics express vi

When using the statistics express vi in LV7.1, I get wrong results for standard deviation. I particular, the VI outputs the mean value instead, but only for certain data sets. Most of the times it works fine. I can not see any problem in this very simple VI. Any ideas?
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Dirk
Attachments:
statistics_problem.vi ‏565 KB

Hello Dirk,
I think you found a bug on the LabVIEW's statistical functions...
I removed that set of data from the array and tried the normal (not express) statistical functions and they return NaN and for the others it's ok!
See attached code.
Paulo
Attachments:
statistics_problem[1].vi ‏600 KB

I found Error in Statistics Express about the algorithm for mode

LabVIEW 7.1 was used. today I acquired a lot of data and analyzed using Statistics Express in LabVIEW 7.1, whereas the results of mode were not correct because I analyzed the data using both Excel and SPSS. so I think there must be something wrong with Statistics Express in LabVIEW 7.1. Attached is the data which mode is 57.24 by SPSS, but the result of Statistics Express showed the result of 32.608.
will someone please help me?
thanks
Attachments:
data.xls ‏29 KB

Hi,
I agree the 2 places of decimals is a cosmetic property and I have no issue with that....
I have my vi setup such that at one call it gets the mode of distances between points on lines. The second time I call the mode it is to get the mode of distances between another set of points. Two separate arrays in a fairly large program. I've attached a shortened sample hopefully the error still appears. Also I was wrong about wiring the intervals wire, this did not change anything.
If I run the 2nd mode operation on it's own without the previous call it works fine, only when there is a previous mode operation does it fail to "re-initialise" and returns the result of the first mode operation.
The only thing I can think of is that the first set of data has many different distances and gives a clear mode, whereas the second set has values approximately the same, with the odd multiple (ie 20,22,19,41,62,20,21,23). However, going against this is the Express Statistics vi which calculates the correct values in the Express Window (double clicking on it and selecting the statistics) but when wiring these to an indicator the result from the first mode operation is returned.
Any suggestions welcomed.
Kind regards,
Leeser
Attachments:
mode_error_example.vi ‏143 KB

Calculating Percentages of expressions in a matrix

I am having difficulty calculating the percent change in an SSRS 2008 report using a matrix and groupings
I am getting errors NaN or infinity or the incorrect %.
Goup 1
Group 2
Actual
Budget
Variance
Percent Change
Actual
Budget
Variance
Percent Change
Type 1
1.55
1.64
-0.09
(5.24%)
1.42
1.53
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Type 2
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Type 3
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Type 4
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Type 5
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0.96
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Type 6
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0.90
0.73
0.1763
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Type 7
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1.41
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0.83
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6.85%
Type 8
2.70
2.65
0.05
1.90%
0.97
1.01
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Grouped by Type
The fields are expressions as follows:
Actual: =IIF(Sum(Fields!ActualDRGWeight.Value)>0,Sum(Fields!ActualDRGWeight.Value) /sum(Fields!Current_Actual.Value),0)
Budget: =IIF(Sum(Fields!BudetDRGWeight.Value)>0,Sum(Fields!BudetDRGWeight.Value) / Sum(Fields!Current_Budget.Value),0)
Variance: =(sum(Fields!ActualDRGWeight.Value)/sum(Fields!Current_Actual.Value))-(sum(Fields!BudetDRGWeight.Value)/sum(Fields!Current_Budget.Value))

Hi ,
It might be because of two reasons :
i)make sure all the Fields involved in calculation are of compatible data type
ii)IIF - Divide by zero error -
http://www.allaboutmssql.com/2013/09/ssrs-divide-by-zero-error-myth-of-iif.html
Suppressing Null or Zero Values at Run Time
http://stackoverflow.com/questions/5471817/ssrs-2008-dealing-with-division-by-zero-scenarios
sathya - www.allaboutmssql.com ** Mark as answered if my post solved your problem and Vote as helpful if my post was useful **.

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Srini

Hi,
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In vendor evaluation, can someone please provide details of how standard report calculates the price statistics. I know the data it uses, so plesae don't copy and paste links to SAP documentation.
Someone please provide a working example so I can see the calculation process.
Thanks.

The effective price store in the info sturcture S013 and when you do the GR/IR that time if any diff will be recorded to the infostructure and based on that system will calulate the price level
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Custom tag attribute calculated by scriptlet expression

Hi,
          If I set the rtexprvalue subelement of the attribute element in my tld to
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          When I include the custom tag reference:
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I had the same problem in a design a couple of months ago and could not get around it so I switched the functionality into code and out of the tag lib.
I take it you are trying to do something like this?
<%
String value="hiworld";
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Calculating RMS value of data samples in RT

I am using CompactRIO 9014 in my control application. I am acquiring data from NI 9215 module. I want to calculate RMS value of data coming from this module for monitoring of the system. I want to include data samples within 1sec to calculate RMS value. I am sampling at 25KHz rate. I want to use RT for processing there a way to do this? I am using Labview 8.6.

suni wrote:
I am using CompactRIO 9014 in my control application. I am acquiring data from NI 9215 module. I want to calculate RMS value of data coming from this module for monitoring of the system. I want to include data samples within 1sec to calculate RMS value. I am sampling at 25KHz rate. I want to use RT for processing there a way to do this? I am using Labview 8.6.
Hi suni,
Yes, you can do the processing on the RT host - that's actually the recommended way of doing things. I suggest using a DMA FIFO to transfer the data from your FPGA to the RT host, however you don't want to make your FIFO 25k elements long. Instead, you can write/read the FIFO in chunks (recommended size is under 8196 elements). Then, as long as you're reading from the FIFO at a reasonable rate on the RT, you should be able to pull out the elements and perform the RMS calculations.
If you're new to FPGA, I highly recommend looking at the examples in Help > Find Examples > Hardware Input and Output > compact RIO. A lot of them demonstrate communication between the FPGA and RT hosts.
Hope this helps!
Misha

"real" RMS

Hi all
I use SCXI-1000 and module SCXI 1313,1125...
I want to measure "RMS" current, from square signal. I use DAQ Assistant, from which I get out voltage and current! All working, tested with constant DC.
I tried in this way:
But RMS Value is incorrect(I know that, because I measure with TRUE RMS MULTIMETER.....). The signal is square and look's like this:
Any ideas or "hint's".

robinson wrote:
Voltage is from 0-16V, "RMS" give values about 8-12, which is incorrect, it must be about 50-70mA...(don't look at signal picture, it's just "example").
robinson wrote:
From 'statistics' I get 'RMS' output , which I connect into DC-RMS, and soo one, from that I can see value of signal(look at RMS value,DC avarage, RMS avarage...), so why I will need additional indicator, if I see value from that...
You know, we try to be professional and polite on this forum. We really try. Sometimes, though, we read responses like this which simply make our head shake. in disbelief.
You know what the difference is between voltage and current, right? If so, how in the world can you say that a VOLTAGE between 0 and 16V with an RMS value "about" 8-12 (whatever "about" is supposed to mean in engineering terms) should actually be 50-70 mA??? That's simply inane. If you are getting a voltage which is proportial to a current then you obviously have to perform the same proportianal calculation to convert the voltage to a current!
Also, the "RMS" output of the Statistics Express VI IS the RMS value. Why are you trying to calculate the RMS value of an RMS value? We cannot "look at RMS value,DC avarage, RMS avarage". We don't have your VI, and you're not showing the front panel. Look at the picture you posted. Do you see the values of "RMS value,DC avarage, RMS avarage" anywhere on that picture?
EDIT: It seems that Dennis pretty much said the same thing at the time I was posting.

How is TOTAL RMS different than AVERAGE RMS

I create spoken-word recordings. One company that I work with specifys that the recording should be at a level that measures between -23 RMS and -18RMS. It appears that audio editing programs label their RMS readings in various ways. I had been using Average RMS but I think maybe this company is using a standard that comes closer to what ADOBE calls TOTAL RMS. What attributes cause Audition to give one value to AVERAGE RMS and another value as AVERAGE RMS?

Total RMS used to be what happens if you add together all of the signals in your measuring time window (in Audition normally 50ms), and perform a RMS calculation on them, and that was a pretty standard way of measuring it. Average RMS in Audition is a little different, though. Reading through the somewhat cryptic help files about this reveals that to all intents and purposes, the RMS measurements will vary at different levels, because some attention is being paid to either Noise Criteria or Noise Rating curves. The lower the level gets with these, the more they favour lower frequencies over higher ones; in other words the figures reflect human annoyance factors rather than a specifically defined measurement criterion. And no, we can't tell you exactly how this is going to work, because the actual curves and weighting figures have never been made public, and it would take me several days to second-guess it from comparative readings. I simply don't have time...
It's been like this for ever. The original design of this was done by David Johnston, the program's original creator when it was Cool Edit, and I belive he's no longer associated even indirectly with Audition these days. Whether information about this is actually documented anywhere at all, I don't know. Questions about it come up periodically, and we can never answer them satisfactorily.
The original Cool Edit manual was just as useless about this. The exact words it uses to describe the Average RMS measurement are "Average RMS Power represents the average power of the entire selection. This is a good measure of the overall loudness of the waveform selection." And it's these words I've bolded that make the difference.
What happens with Total RMS measurements now seems to be a little different, and you end up with a figure much closer to a LUFS reading (you get this acccurately at the bottom of the statistics panel in CC). I know (because this is relatively recent) that the way the LUFS figure is calculated is according to the BS1770-2 standard - and that takes the whole program dynamics into account. What appears to happen with Total RMS in Audition is that it appears that an average of all of the windowed measurements, and that this in general turns out to be pretty close to the LUFS value as a rule.
Now, judging by the numbers they've quoted, the chances are that the company you are working for is using the recent standard for what you're doing - so if you are using CC, then it's pretty easy - select the whole waveform and quote them the value shown at the bottom of the screen. If you aren't using CC then there are several free LUFS meters available as VST plugins.
My personal view on this new standard, FWIW, is that it's a complete waste of time. It certainly doesn't achieve what it sets out to, or failing that all the broadcasters that use it have no idea what to do with it. And that very much includes the BBC, I'm afraid. The standard is supposed to keep overall programme dynamics within a certain loudness range, and save viewers/listeners having to adjust volume levels between programmes. And, it fails at that pretty comprehensively. Quite frankly, when it comes to broadcast dynamics standards, they'd have been better off forcing everybody to use the same settings on an Orban Optimod; that would almost certainly have worked better!

Expression Builder Question

I am trying to convert some existing sql to use TopLink ExpressionBuilder. I have a particular type of thing which I can't find a good solution for.
I want to include a calculation, so for example, I want to say
Where MY_COLUMN * 10 > REQUIRED_VALUE
The only way I've managed to do it so far is to use the appendSQL() method. This gives me a problem because this method is deprecated and I can't see what I should use instead. Secondly, I am using a column name in this bit of SQL, if I try to do it 'properly' and join the SQL with a get for my mapping item which maps to MY_COLUMN then add some more SQL it all falls to pieces. This means I have to 'hard code' my column name in the SQL which is not where I want to be.
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You can use the ExpressionMath class.
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RMS calculation in Statistics Express

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