10-11-2016 07:37 AM
Hi,
I'am using Butterworth filter in FPGA Code labview with PXI7841R.
I wana put a frequency less than 50mHz but i can not introduce i modified Sample rate parameters wchich allows to put less than 50mHz frequency but the behavior is not the same.
i want to introduce cutoff frequency Fc=2mHz Fc=10mHz with 1order filter in FPGA math.
Thanks for future advice.
10-11-2016 08:55 AM
You'd probably be able to get some advice from others if you attached a VI that demonstrates the problem you are having.
Perhaps you hit a limitation of LabVIEW. Perhaps it is a mistake you made in your cdoe. But we can't tell unless you provide something we can work with.
10-11-2016 09:23 AM
Code is very simple i have simply input signal and out put signal and i wana modifie cutoff frequency.
i found an exemple of IIR filter i chosse butterweorth filtre and i modifie cutoff frequency with desired value like 2mHz and 5mHz and it work perfectly as mentionned in figure but i can not use it in FPGA code.
i must use FPGA math library with butterworth filtre which is limited at 50mHz.
10-11-2016 09:27 AM
Those are just screen shots. They aren't VI's.
And please provide more description besides it "it doesn't work". In what way does it not work. Do you get an error message? Do you get data, but it is wrong? Does your computer blow up?
10-11-2016 09:32 AM
it means that the output signal is not like desired output signal as founded in IIR filter (which work perfectly) and in theorical calculation of 1ordre filter desired signal is known by maths.
the problems is in the configuration of sample rate and cutoff frenquency.
10-11-2016 10:18 AM
10-11-2016 11:40 AM - edited 10-11-2016 12:27 PM
Of course 5mHz is an awfully low frequency (200 seconds per cycle), so why would you need an FPGA for that in the first place? Maybe some counter is rolling over twice.
10-11-2016 01:44 PM
i configured it many many times but there is no solution:
First i considered default configuration of labview with :
cutof Frequency : 50mHz
Sample rate: 50K S/s
here with 50 K S/s its limited to 50mHz
Then i putet :
cutof Frequency : 20mHz
Sample rate: 2 S/s ==> ouput signal its zero.
and then
cutof Frequency : 5mHz
Sample rate: 50m S/s ==> ouput signal its zero.
Same problem
10-11-2016 01:45 PM
My physic system i wana have this curve with Fc=5mHz.
i must have this result its no logical to not programe this in FPGA !!!!
10-11-2016 02:12 PM
@Rayden wrote:My physic system i wana have this curve with Fc=5mHz.
i must have this result its no logical to not programe this in FPGA !!!
What the logic behind your "not logical"? Please explain. Your frequency is so low that the RT system would have no problem dealing with it accurately. Maybe you can look inside the filter VI and rewrite it to your desired specifications, hopefully without running out of FPGA real estate..