How can I measure the frequency of an analog signal?

Hi, I am trying to measure the frequency of VAC signal coming from a gas turbine engine at my university. If I can get the values of frequency, I can determine the speed (RPM) of the engine. I am fairly new to LabVIEW and I have been looking through manuals like crazy in order to find out how to obtain the frequency. I have measured the signal with an oscilliscope and the highest frequecy will be about 1.5kHz. I am currently using a USB-6218 and it can collect the voltage signal with ease, but it won't give be analog frequency so simply. Can anyone explain a way for me to obtain the frequency values? And if you could show or tell me in a very simple way (because I am not very fluent in LabVIEW yet), that would be amazing! Thanks!

Check this out:
Attachments:
RPM.vi ‏17 KB

Similar Messages

How can I measure the frequencies of two analog input signals simultaneously?

Hi
I have two AI signals, and I need to determine the frequencies of those signals. The frequencies range from 1-125Hz. I currently have a VI where I can sample one of the signals for 1 second (sampling at 300 Hz for 300 samples) and determine the frequency.
I need to read two signals at the same time and get both of the frequencies at the same time, but I can only figure out how to read them individually, so I can read one signal, then one second later I read the second one, then I read the first one again, then the sceond one, etc.. How can I read two signals simultaneously?
Thanks
Attachments:
FreqMeas11.vi ‏41 KB
FreqMeas11.PNG ‏18 KB

"at same time", this depends on the hardware, you can do as has been previously stated just set up a 2 channel acquisition and you will get 2 sampled waveforms back. Most hardware A/D as multiplexed and true simultaneous sampling is not done. At 125Hz this is not an issue unless you are interested in very small phase changes between the samples. just keep this in mind if you are expecting samples to be completly synchronized.
Paul
Paul Falkenstein
Coleman Technologies Inc.
CLA, CPI, AIA-Vision
Labview 4.0- 2013, RT, Vision, FPGA

How can I measure the hertz in a wave form?

How can I measure the hertz in a wave form?

As an example, this is from BBC Technical Requirements for HD material:
3.1.1 Stereo line-up tones
All stereo tracks must use EBU 1KHz tone (left ident). All tones must be sinusoidal, free of distortion and phase coherent between channels.
Digital Audio Reference level is defined as 18dB below the maximum coding value (-18dBFS) as per EBU recommended practice R68.
See also:
http://www.bbc.co.uk/guidelines/dq/pdf/tv/tv_delivery_to_network_programmes_v1.2-2011.pdf
for full document.
And for BBC Radio:
Not every Network requires tone. Check the delivery requirements with the commissioning network or click here.
Reference tone, where used, should be at -18dBFS or PPM 4 on A, B and/or M.
If submitting material with reference tone, tone and programme material must be have been monitored and measured through the same technical chain. The level of the tone must be equivalent to 0dBu and no less than 8dB below peak audio level for the programme material.
THE LEVEL OF TONE MUST HAVE A KNOWN RELATIONSHIP WITH THE LEVEL OF THE PROGRAMME MATERIAL AND THIS MUST BE STATED; for example: “Tone at 8dB below peak programme level”.
As a newcomer to digital sound (my background is camera) I confess to being somewhat confused. We are normally told to record at the highest level possible. So for voice podcasts I tend to record at about -6dB below peak for maximum volume, distributeds on MP3 files.
But I can underatand that televison and radio especially for analogue transmission) may have limited headroom, hence the requirement for -18dB peak = 0dBM.
I remember when we first rented out Digital Betacam cameras, some recordists were recording almost everything OVER -18dBM.
I suspect that until we have an all-digital world, these requiremnents will still be in place.
Many thanks to all. It's a ghreat community!
Brian Rose

How can I measure the Graphics Card usage? I.e. percent load

Hello,
How can I measure the Graphics Card usage, like with the processor in Task Manager, but instead giving a percentage usage for the graphics card instead? Is there an easy way to do this, or would it require a lot of code? Is it even possible?

Ah, so It's unlikely that Java3D will include anything for reading this data then? I was really aiming at measuring the GPU usage under this API which although i have limited knowledge using, I do at least have some knowledge - I wouldn't have a clue how to access any other API's!
I'm using an NVidia TNT2 card at the moment, which is quite old.

How can i measure the speed of the fan in sound and vibration signal simulator box

how can i measure the speed of the fan in sound and vibration signal simulator box
provided the values tach out:2 pulses/revolution and maximum speed = 6000rpm

Hi. I tried your suggestion and I could not get it to work well. In
fact it worked better without the running average (which suprised me).
I also played with the number of data points but still could not get it
to work well.
Do you have any other suggestions on how I could sort this problem out?
I
have attached a screen shot of the signal. To recap, I'm trying to
measure the'y' position of the flat regions of the signal. The signal
does not have a constant level, so this 'y' position varies with time
in a non-unform manner.
I am currently differentiating
the signal and selecting the y position when the differential is equal
to zero (within a tolerance band).
In the screenshot, the
signal has been zeroed using the method I have described above.
However, it occasionally has glitches which may be caused when the code
picks up a zero gradient at a peak or valley in the signal.
I therefore need some kind of algorithm that only measures the position of the flat regions.
Many thanks
John
Attachments:
screenshot.gif ‏121 KB

How can I measure the copy speed of my compact flashcard to folder?

how can I measure the copy speed of my compact flashcard to folder?
I dont have a stop watch.

Hi Steve Zavodny;
Generally compact flash cards or basically slow because of them being flash memory and USB. What are you after here?
Allan

How can I define the intermittency factor of a signal?

Hi everyone,
I want to ask how can I determine the intermittency factor of any signal.
The intermittency factor is a ratio of the time of high frequency distortion in the signal to the total time of the signal. So, Intermittency=time_turbulent / time_total.
I have attached an image file and original vi with source vis to show the high distortion time in blue lines. I want to determine the total time of these distortion in the blue lines. Then I will divide this total time corresponding the high level distortions in the blue lines by the total time of the signal to calculate the intermittency.
How can I achieve this? Could you please help me? Regards,
Attachments:
image.jpg ‏326 KB
Unsteady Pipe Flow Analysis_Shortened Format.vi ‏643 KB
subvis.zip ‏967 KB

mechen,
It is not clear to me whether your problem is (1) how to measure the time or (2) how to determine the presence of the high frequency distortion. The counters to which Paul B. referred are related to (1). I cannot look at your VI from home, so I do not know what you have tried.
You generally get better help on this Forum if you ask very specific questions. Asking someone to do the whole job for you, especially when you have not provided all the specifications, is much less likely to get you the help you want.
Lynn

Can I measure the frequency from all PFI pins?

I am using a PCI-6229 DAQmx card. I am trying to measure the frequency from pin PFI 5. I have been successful in measuring frequency from PFI0 and PFI1 but for some reason I am not able to measure on other pins. When I run the run the DAQmx Read sub VI it times out like it is not reading anything. I am using the same sub VI I created to measure 5 as I did 0 and 1 so I know that the VI is working. What is the matter? Are there only certian pins that I can measure? Would the sub VI time out because there is no signal on the pin?

Hello Flowserve1,
Thanks for your post!
The basic answer to your question, "Would the sub VI time out because there is no signal on the pin?", Is yes if there is no signal coming into the pin your are bring a signal in on. It sounds like you were able to do a "frequency" measurement on PFI0 and PFI1? Usually the counter tasks are used for such a measurement. How are you performing these frequency counter tasks on your PFI lines? It looks like on the pin read out that PFI0,1 and 5 are for digital tasks and PFI routing lines. Are you internally routing your signals to other places? If you want to measure the frequency using counters, this board has two of them so use Ctr 0 and 1 gate or source to make these measurements. Let me know if any of this helps you and perhaps you could post a piece of your code that you are using to make your frequency counts.
Cheers!
Corby_B
http://www.ni.com/support

How do i measure the frequency of a sine wave using a field point counter module

I need to measure the frequency of the sine wave using field point. is it possible and if yes how. do i need to convert the sine wave signal to square wave. Please let me know.

It probably would be easiest to convert the sine wave to a square wave with a simple external circuit and then use a counter module to measure the frequency. There is a shipping example in LabVIEW that shows how to measure frequency with a FieldPoint Counter module.
JRA

Help with measuring the frequency of a pulsing signal

Hi,
I am trying to use LabView to measure the flow from my ultrasonic flow meter. The meter sends a pulse for evey 10 litres of flow: I am picking up the signal in LabView without any trouble - it's basically a square wave that pulses at 10V and goes back down to 0V for the same duration.
All I need to do is measure the frequency or period of the wave, but I have had no luck with any of the vi's. They seem to focus on the wave when it's either at 10V or at 0V and return the period as infinite or 0.
I then attempted to program a sequence which returned true if the signal was =1 (the rising edge of the pulse), if true it would go to the next step, check again if =1 (falling edge), if true go to the third step and check if signal =1, and time that sequence, giving the period of the wave. Unfortunately this didn't work either.
Any suggestions?
Cheers,
Liam

Hi, I have the same problem - my LabView edition is Student so I don't think I can access them.
Unfortunately the problem is still persisting. I have been working with someone who is quite experienced with LabView and he can't solve the problem either.
There was some progress when I used the Trigger and Elapsed time .vi's to measure the time between rising edge pusles. Since the pulses were quite slow, by putting the period-to-flow conversion equation in, the flow could seen reducing to a minimum value as the elaspsed time increased to the full period. I have fitted new, more accuarate flow meters into he pipes which now send 100 pulses for each litre of flow. These flowmeters now pulse so quickly that it's impossible to see what the minimum flow value is to get the flow.
If anyone knows of a way to select the maximum time value (i.e. the full length of the period of a square wave) that would be one solution to the problem. Any other suggestions on the best way to measure square waves would also be gratefully received.
Thanks in advance
Liam

How can I calculate the frequency of a 2-4Hz three phase sine wave in 50msec?

I want to calculate the frequency of a sine wave using either all three phases or just one, but I want to know the frequency after 50 msec, I don't want to have to wait for a full period.

I have a mathematically sound suggestion but I do not know how well it will work in application. Most period measurements measure the time between a full period or several periods to eliminate the error introduced by the measuring device. Essentially the device error is made insignificant.
Mathematically you can do much more but there is a tradeoff between recording less information and knowing (or assuming) some values. For instance, if one knew the amplitude and could calculate the derivative of the signal, one could calculate the frequency. A sine wave can be represented by the function: A sin (BX)=C , where A is the amplitude, B is the frequency, C is the present measured value. If the equation is solved for X, we get: X=(sin^(-1)(C/A))/B. The d
erivative of the first equation is AB cos(BX)=C. If the equation for X is now substituted into the second equation, we get, AB cos(B (sin^(-1)(C/A))/B)=C. Solving for B we get B=C/(A cos(sin^(-1)(C/A))). Remember, we already know A and C, so we are done.
Practically every step and assumption in the above argument introduces possible error which will affect the accuracy of the frequency. Unfortunately it is a trade off and that is why at least a whole period needs to be measured to get an accurate frequency.
Jeremy Braden
National Instruments

How can i measure the time between two successive rising edges ,using digital input ..

Hello
I'm trying to measure the time in seconds between each two successive rising edges on a digital input .
Till now I have managed to detect the rising edge ,increment a counter with each rising edge ,and snap the time at which the rising edge happenned
all I need now is to subtract the current rising edge time from the previous rising edge time in order to calculate (T) which can be 1/frequency and display it in realtime to the user.
but I don't know how to do this
Can somebody please help me !!!
note: the time that I'm measuring ranges between 200 ms - 2 seconds
Solved!
Go to Solution.
Attachments:
Counter without time.vi ‏11 KB

Cheers for that. It's always a good idea to post your SubVIs as well - the problem could be in one of those.
To help you out:
You already know how to use shift registers so why not use one again for time? Create a new shift register for the time then simply compare the "rising edge time" to the the previous time stored in the shift register and then write the new time to the shift register.
Just a few other pointers:
1. You'll want to initialise your shift registers ie wire a constant to the left hand register outside of the loop. This will cause the register to be reset each time the program is run. This is so that your counter will start from zero each time you run your code.
2. You don't need to use the "greater than?" compare function with boolean as they can only be true or false (1 or 0)! The "Equal?" function is what you should use here.
3. Lastly, it's a small thing but you can use the same tunnel that feeds into a case structure in each of the cases - no need to create two tunnels for the true and false cases, use the same one.
-CC
"If anyone needs me, I'll be in the Angry Dome!"

How can I measure the time between each two successive rising edges ,using Digital Input ?

Hello
I'm trying two measure the time in seconds between each two successive rising edges on a digital input .
Till now I have managed to detect the rising edge ,increment a counter with each rising edge ,and snap the time at which the rising edge happenned
all I need now is to subtract the current rising edge time from the previous rising edge time in order to calculate (T) which can be 1/frequency and display it in realtime to the user.
but I don't know how to do this
Can somebody please help me !!!
Solved!
Go to Solution.
Attachments:
Counter without time.vi ‏11 KB

Woah!
Sorry Apok, but your code is becoming way too complicated/messy. I don't think that all of those shift registers or boolean conversion/operators are needed at all.
If you want to measure the timing between two button presses then this is a different (much less complicated) way. It simply records the timing of the button press into a shift register then compares the two.
Spoiler (Highlight to read)
Of course this is a very quick and basic solution just to show you that it can be much simpler than you are making it (remember to use the mechanical actions of the buttons to get the behaviour you want).
A better way would be to use an event structure looking at value changes of the buttons to determine the timings between clicks.
-CC
"If anyone needs me, I'll be in the Angry Dome!"
Attachments:
Time between clicks.vi ‏9 KB

How can I measure the phase difference of two input signal?

Hello,
I'm trying to measure the phase difference of two input sine waves with the
same frequency.
Is there anybody how I can do this with labview?
Thanks,
Dae-han

This is my case! I have TDS3034 which can measure phase. However when I open Read Waveform Measurement vi that comes with tkds30xx.llb, I have a number of options under "measurement function" but not the phase measurement. May be I need another vi to do this?

How can I find the frequency of a signal from a turbine flowmeter?

My turbine flow meters output a voltage signal frequency. Is there are way that I can find the frequency in LabVIEW? Right now I have the flow meters wired to my card as analog inputs. Maybe I need to wire them in differently.

Dear moebeth,
To address your question, can you include more information about the flow meters? As far as I know, turbine flow meters can have outputs of analog voltage, analog current, frequency/pulse, or switch.
If the meters are outputting a voltage, then connect it as an analog voltage input and use the analog voltage virtual channel.
If the meters are outputting a frequency or pulse, connect it as a counter input. With the counter input, you would need to program in LabVIEW without using a virtual channel. Instead, you would use the counter VIs. There are shipping examples included with LabVIEW. Measure Frequency (DAQ-STC).vi can be used just by pressing Run if you wire the signal into the source of whichever counter you want to use and th
e ground into DGND.
Let me know if you have any further questions or if this does not resolve your issue.
Thanks again and have a great day!
Chad AE
Applications Engineer - National Instruments
Attachments:
Frequency.zip ‏45 KB

How can I measure the frequency of an analog signal?

Similar Messages

Maybe you are looking for