LabVIEW
Problems with filter
Solved!
Hello
Iam trying to filter my data with lowpass FIR filter but for some reason filter have problems with nyquist criterion but iam receiving data every 20 ms which should be 50 Hz of frequency and filter only works when i set cutoff frequency to 0,5 which means filter thinks that my sample frequency is 1 Hz which cannot be right and if i increase cutoff frequency i get error message 20020 with possible reasons that my cutoff frequency is too high. Any ideas why is that a case? Without the filter everything looks fine as shown in picture and i also attach picture of filter settings.
Hi enjoyer,
@enjoyer_1 wrote:
Any ideas why is that a case? Without the filter everything looks fine as shown in picture and i also attach picture of filter settings.
An idea: there is something wrong with your code!
Unfortunately you choose to hide the code from us and also hesitate from attaching that code! All we get is an image, showing the configuration dialog of an ExpressVi covering the remaining code…
(When you attach code: downconvert to LV2020 or LV2019 to receive a broader audience.)
Lots of people don't have 2021, use File- Save for Previous in 2019 like GerdW said. Even better use 2017 or so.
Hi enjoyer,
did you read my comment about downconversion of your VI before uploading? (File->Save for previous…)
Hi enjoyer,
@enjoyer_1 wrote:
Iam sorry i didnt really read that one.
So you don't care about the answer you got?
Your filter ExpressVI has no input data, so it's ok to yell about the Nyquist criterion. You need to provide data!
What is the sample rate of your data? How many samples to you receive?
Btw. LabVIEW has a numeric constant named "pi"…
Iam sorry i just wanted to quickly send u my VI so maybe u will ahve an idea what is wrong. Obviously i had input data in my filter and according to NI site iam supposed to create waveform with time (dt) and it will fix my issue but it didnt and iam also sending u picture of how my data are looking and above them are filtered data (nothing) . As i said iam receiving data every 20ms which should be 50 Hz frequency
Your problem is that you're only giving the filter a single data point. A waveform chart automatically retains its history. When you multiply it by pi then create a 1D array, you're making an array with a single element in it. When you feed it to a waveform chart, the chart maintains the history, but the array doesn't since you're creating a new array each time.
Use a shift register and build the array every loop and switch to a waveform graph, which displays whatever is sent to it and doesn't maintain history.
Give this a shot:
Also, you should clean up your block diagram. It's honestly not the worst I've seen but you'd benefit from straightening out your wires, removing all of the extra Build Arrays, etc. The big thing is to actually label your plots, that will make things a LOT easier to read.
Also, I didn't know you could use a Type Cast to convert an array to a cluster like that. Honestly a little surprised that it works. Anyone else know if that's an intended way to convert from an array to a cluster like that? I always just use Index array/bundle.
