Point-by-point Frequency Measurement

I am using an anemometer to measure wind speed. The device puts out an AC signal, calibrated such that 0.75 m / s / Hz.
I have attached my DAQ vi, which is reading 16 different channels simultaneously. It is sampling at 120 Hz (double the 60 Hz maximum rating for the anemometer), and acquiring each sample individually.
This means that I have a stream of data points. I can plot the turbine wind speed easily on a chart (Channel 11), and you can see the AC signal very clearly. However, I don't know how to determine the frequency, since it is a stream of single data points, as opposed to an array of datapoints.
I'm a bit of a Labview beginner, and I have searched for a solution to this for several hours now, so hopefully someone here can give me a hand.
Sorry for the mess of wires; that's what happens when I click the clean-up tool button!
Brian
Attachments:
DAQ.vi ‏27 KB

You can try the attached code.
Attachments:
point-by-point frequency estimation.vi ‏11 KB

Similar Messages

How can i mark user defined points in amplitude versus frequency graph?

i have an array of frequencies and amplitudes . i need these values to be displayed on x-axis frequency values and y axis amplitude values . one fixed default plot should be continuously visible in this graph and then i wish to mark few user defined points in the same graph, save these two plots in the same graph and then take a print out of the graph.
Kindly help this is regarding my master of engineering project where i am trying to biuld an audiometer (for testing hearing sensitivity) and i am going to interface labview with ardiuno micrcontroller and my hardware devices.
so kindly help.
thank you.
vanashree
Solved!
Go to Solution.

hey....m able to generate a multiplot...
it works...
i have placed two fixed plots on it...
now just one thing remains..i need to place user defined points on the same plot...i have attached my work..i have labview 7.1
Attachments:
24th home try me.vi ‏157 KB

Frequency measurements using NI cRIO 9073 and NI 9425 or NI 9422 modules

Hi everyone!
I'm trying to measure two frequency signals using a cRIO 9073.
I'm already using a NI 9425 module for digital inputs.
I need to measure two (2) frequency signals.
Is it possible to use this module (NI 9425) or NI 9422 for frequency measurements either in Scan Engine or FPGA mode?
In case it is, if you could point me to any example, it would be appreciated.
I'll try to be more explanatory:
These two frequency signals are in completely different ranges.
The first is a frequency signal from a DC motor tachometer and the second one is from a mass flow meter.
So the frequency ranges vary from KHZ for the tachometer output, to Hz for the MFM output.
The rest of the channels on the module are simple Digital Inputs.
Also, I have the option to use a NI 9422 module if NI 9425 is not appropriate.
Thanks in advance,
t81

t81,
It is possible to make frequency measurements with either the 9422 or the 9425 but each will have its own limitations in the range of frequency it will be able to accurately measure.
A few things to know:
1. What are the frequency ranges for each sensor (tach and MFM)? More than just knowing Hz/kHz will be helpful.
2. To what accuracy do you need to measure these signals?
The 9422 supports a specialty digital configuration counter input that can be configured for frequency measurement (see link)
http://zone.ni.com/reference/en-XX/help/372603F-01/riohelprt/crio-9422_rt/
The specialty mode is only available when using Scan Interface mode, not with FPGA.
But the max clock rate in the specifications for the 9422 is 4kHz so this may not be sufficient for the tachometer. I believe this is the max rate at which the module will update its state no matter how fast the underlying software (RT controller) is running.
The 9425 has a higher clock rate (~140kHz) but doesn't support the specialty digital mode mentioned above. It is also a software timed only device but this shouldn't be a problem if you use FPGA.
Dan

Triggering frequency measurement with 9402 and cDAQ

Hi all,
I'm trying to take a speed measurement off of a shaft using a hall effect sensor and a 9402 module in a 4 module cDAQ 9174 chassis. I've used the low frequency measurement example using DAQmx but if the shaft isn't spinning I get a timeout error.
Two questions, is there a way to use the Express VI's to accomplish this and how do I create a trigger to start the measurement?
-Ian

Why not clear the timeout and report 0 RPM. The timeout is 0 rmp but you dont want to wait forever and block program flow.
Paul Falkenstein
Coleman Technologies Inc.
CLA, CPI, AIA-Vision
Labview 4.0- 2013, RT, Vision, FPGA

Digital Frequency Measurement for cRIO

Hi,
I'm new to LabView, and I'm having problems setting up a VI for frequency measurement. Any tips would be greatly appreciated!
Task: I am using a cRIO with a digital I/O module (NI 9403). My goal is to connect the sensor that I am using (a MAXIM 6576 temperature sensor with period/frequency output in the form of a square wave) to the cRIO and have a VI measure and output its current frequency or period.
I've tried working with the Count and Period.vi, but when I tried to compile I found out the 9403 module does not support SCTL. I also looked at a thread that was posted in 2009 (http://forums.ni.com/t5/Counter-Timer/beginner-stuff-cRIO-digital-frequency-measurement/td-p/826656/... that discussed a similar problem, but when I tried using the Host VI I got the multiple error messages saying "Function not supported in current target". This happened even when I tried using the original Count and Period (Host).vi with no modifications (but the original Count and Period (FPGA).vi works just fine).
I don't know how to approach this problem - should I be using FPGA or Scan Interface mode? Are there any basic examples of frequency measurement or digital counters that do not involve NI data acquisition devices? For a basic counter, how would you set up the VI so that it could measure the period or frequency based on the counter values?
Thanks a lot for your help!
Andrea

Hello,
A great place to get started when using a cRIO is the NI CompactRIO Developer's Guide. It will explain both Scan Mode and FPGA. The difference between them comes down to the functionality and what you would like to complete in the program. The simpler of the two is Scan Mode but you have more functionality with FPGA.
We offer a lot of good examples in our NI Example Finder by going to Help >> Find Examples. In here you can narrow the examples by hardware or just browse to different categories. We do have a counter example that will work with the NI 9403 you can get to the example by going to Hardware Input and Output >> NI Scan Engine >> Module Specific >> Digital Input >> “Digital Line Input – cRIO.lvproj.”
Regards,
M. Whitaker
ni.com/support

Low frequency measurement from Parallel Port

Hi there...
I need to calculate the "on" and "off" time and duty cycle in pulse form from a parallel port. By making the circuit in 5 or 0 V, I just simply put it in my parallel port. The problem comes when I need to measure a very very low frequency. In this case, I want to measure the duty cycle from my operated refrigerator. I need to know when the thermostat goes "on" and when it comes to "off". In my experience, the thermostat will be "on" in about 5-10 minutes and "off" in about 20-30 minutes. So, the pulse might be take for a long periode each.
I've tried with Timing and Transition Measurement wizard or even by using Pulse Measurement.vi which is included in Waveform Measurement category. It only works for 2 Hz and . If I try to set it with 1 Hz or below, it comes the message :
"Error -20308 occurred at Timing and Transition Measurements -> Untitled 1
:4" (waveform index 0 of 1)
Possible reason(s):
Analysis: The waveform did not cross the mid reference level enough times to perform this measurement. Check the signal length, reference levels, and ref level units."
Could someone help me please ?
Regards,
Ricki

here is a quick shot to give you an idea
Greetings from Germany
Henrik
LV since v3.1
“ground” is a convenient fantasy
'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'
Attachments:
port logger.vi ‏22 KB

Changing frequency measurement

Hello,
I´ve sampled a signal from a hall sensor on a belt pulley. I get six pulses per rotation. So I get a higher frequency on a higher belt speed.
How can I analyse the frequency or pulse width for each pulse with LV?
Best regards,
Andy

Andy,
Typically period measurements are used when pulse by pulse data is needed. You could either measure the width of a pulse or the period of a cycle.
In either case you need to define a minimum speed, or maximum pulse width or period you want to detect. When the shaft slows down the time between pulses or edges gets longer and longer. Make sure your period measurement process has some kind of timeout or maximum time limit so that it does not hang up waiting for another edge onyour signal.
Lynn

Frequency measurement with PCI6624, timout problem at startup, i.e measure 0 Hz.

I want to use my PCI 6624 for measuring of frequency signals from a gear flow meter. The problem is that when I start running the VI there is no pulses from the flow meter and the VI stops to run and I get a Timeout error message. I.e is it possible to measure 0 Hz with the 6624 input used for frequency measurement?
With hardware from IOtech and Daisylab I don`t have this kind of problem.
/Thanks in advance

Having similar problem,
Did you manage to resolve the issue?
I have attached the the solution given by NI for error code 200474, if its any use. The problem I have just found with this Vi is that if one channel has no signal it forces the other channel to grind to a halt. This problem has existed for me on the cards being used in this project PXI-6289 and PXI-6236, also other DAQ cards used in a different project earlier in the year.
It seems to be a serious flaw in the application of the NI DAQ cards to general purpose data logging where counter signals might not be connected by the end user or they are very low frequency and the whole system hangs.
Labview Version 8.5
Labview Version 8.6
Labview Version 2013
Attachments:
FLOWMETER_21.vi ‏37 KB

I have an optical sensor how do I get a RPM or frequency measurement?

I have three optical sensors on a gyroscope rig connected to
a 6601 card producing a square wave of 0-5V. I can get an edge count. But how do I get an RPM or frequency
measurement?

Dear Ian
I have to say I’m not having a lot of luck with the example finder. I have three optical sensors all hooked up to LabVIEW. I can count the pulses no problem, I just don’t seem to be able to connect a clock. As I think I want a “Period Measurement” or a “Buffered Period.”
Best wishes
Robert

Point-By-Point filtering for Blackfin

Hi,
I am evaluating the embedded module for blackfin for a project, where i need to do some real-time-filtering during ADC.
In normal LabVIEW (not for an embedded target) I would do this using PointByPoint-filters. But as these VIs all seem to use floating point data types, they are not really suitable for my application.
I couldn't find any way to do point-by-point-filtering using the blackfin-optimized VIs by now. So my question is, if there are any blackfin-specific point-by-point VIs that I just did not see (perhaps not available in the evaluation version?) or if there is any other way to accomplish real-time-filtering with the existing VIs.
Thanks,
Jan

Hi John,
The “Inverse Chebyshev Filter PtByPt.vi” is reentrant. When you
open the SubVI, the title should say “clone” in parentheses. Each clone runs in
its own memory space. You cannot modify a reentrant VI unless you close all
referencing VIs.
The “Inverse Chebyshev Filter PtByPt.vi” is also part of a LabVIEW
library. (C:\Program Files\National Instruments\LabVIEW 8.5\vi.lib\ptbypt\NI_PtbyPt.lvlib).
This Library is password protected. Also you do not want to modify something
shipped as standard along with LabVIEW.
There is a way around this though. Open the “NI_PtbyPt.lvlib”.
From the menu select File >> Save As. This will duplicate the entire
Library to a new location. Now open the copy “Inverse Chebyshev Filter
PtByPt.vi” and modify it to use Inv Chebyshev co-effecients. You can now use
this modified SubVI. I did try this (in LabVIEW 8.5) and the outputs of the
Point by Point and Array functions were the same in your Demo program.
Again, I cannot comment if this is a bug in LabVIEW or we
are missing something. It would be best to contact NI or wait for someone from
NI to comment on this forum.

Frequency measurement with High Speed Digitizer using External Trigger

Hello:
I have a

Hello Brooks:
Thank you for attention !
I will try to explain my application:
I need to measure a signal of a speed/position sensor. This sensor works with hall effect principle and is placed in front of a wheel with some teethes. Is used for automotive purpose in CAM and CRANKSHAFT applications. So, I need to measure period, duty cycle, rise time, fall time, Vpp, Angles for each teeth x encoder, everything from 40 to 7500 rpm.
I'm using CH0 to measure a signal of this speed/position sensor.
I'm using CH1 to measure a signal of an encoder connected to wheel.
I'm using EXT Trigger to sync acquisition with encoder's INDEX signal.
I need to measure the frequency of EXT trigger to know the instantly speed of the wheel.
So, If I know that my encoder has 2048 pulse/rev, I can measure FFT_FREQUENCY of CH1 with scalar measurement functions and calculate the speed !
The NI-Scope is wonderful because it can measure a lot of things automatic and fast, like period, frequency, duty cycle, rise/fall times ...
Now I have one more question:
I want to use 10:1 attenuation but I can't use a common probe. I want to connect the CH0 to sensor with a special connector.
I've tried to make the same circuit with 9MOhms and capacitor like explained on site, but I reached bad results. The industrial probes has special characteristics for capacitance and noise rejection.
Do you know how can I solve it ?
Thank you.

Why does my point-by-point signal generator give a flat line?

Hi all,
I am using the point-by-point VIs for the first time and am trying to generate a square wave using them. However, when I plug the output from a point-by-point square wave generator, it just gives a flat line (using both default values and various values for the other parameters). But it works fine if I use the point-by-point noise generator, it shows up fine in the chart. Any ideas?
Cheers
Solved!
Go to Solution.

hello ,
i think you surely forget the time base ...
also take care to use step time < 0.5*fmax
see vi joined
@+
Tinnitus
Message Edité par tinnitus le 12-15-2008 06:37 PM
CLAD / Labview 2011, Win Xp
Mission d'une semaine- à plusieurs mois laissez moi un MP...
RP et Midi-pyrénées .Km+++ si possibilité de télétravail
Kudos always accepted / Les petits clicks jaunes sont toujours appréciés
Don't forget to valid a good answer / pensez à valider une réponse correcte
Attachments:
square.vi ‏10 KB

NI-6602 Two Channel Frequency Measurement using Traditional NI-DAQ and LabView 8.2

I have been trying to program for some new experiments and have a vi setup to record the time-of-arrival for a signal using buffered event counting on two channels. We really wanted to be able to measure the frequency of the incoming photons on both channels and thought we could just make a sub vi using simple event counting and count the number of rising edges on a source pin for a second and report that number and repeat the measurement until we were done..
All of our vi's have to be programed using the Traditional NI-DAQ drivers as the NI-DAQmx drivers do not play well with the FIFO overwrites on the 6602 card that occasionally occur in our measurements (high instantaneous count rates from bursts of photons). The way other groups using the 6602 card and labview have dealt with this is to ignore the error that come from the Read Buffer.vi used with the Traditional NI-DAQ drivers when a FIFO overwrite occurs. Trying this same technique with the NI-DAQmx drivers has not worked so we are stuck with the old drivers.
With this all said I made a vi that counted the freqency on one counter just fine but when I adapted it for two channels it doesn't like me anymore
I attached the llb file and any comments would be greatly appreciated
-Shane
Attachments:
Counts per second.llb ‏202 KB

Hello Sprice,
Browse the shipping examples according to “Directory Structure” and then select
DAQ to find the Traditional DAQ examples.
There a lot of examples that are written for counters (Counter >>
daq-stc.llb >> Count Edges (DAQ-STC).vi).
What kind of signals are your photons creating? Are they TTL compatible at a certain
frequency? You don’t care about overwriting
your buffer?
Respectfully,
Rob F
Test Engineer
Condition Measurements
National Instruments

Using field points how the dc voltage measurement is done?

i am new to labVIEW.. Using cFP-AI 100 i am trying to measure a dc voltage [5volts].. all the field point items are configured on MAX. when the example VI provided runs there is error indicating that the connection is broken or network module is not pwered on.. but i have checked both .. What may be the problem?

Hi ELUE,
When you say "all the FP items are configured on MAX," does that mean you can see and connect to the device? Can you take readings in MAX from the FieldPoint module I/O menu under the Data Neighborhood?
If you're able to read from the I/O menu you are probably using the default I/O point in the example. It's usually necessary to choose the I/O point before running the example.
Cheers.
| Michael K | Project Manager | LabVIEW R&D | National Instruments |

FPGA Many Many Frequency Measurement

Hello all,
I am trying to measure the frequency of some 50 PWM signals that only goes up to 300Hz. I use the R-7833. Attached is what I am using to measure ONE PWM signal. Now, the problem is: Is there a way to use the same code to measure the 50 PWM signals without copy and pasting the same code 50 times. Note: I have tried to make them into sub-vi's, but have failed.
Solved!
Go to Solution.

Hi Bladhart,
This is a good case when moving the I/O node and loop structure outside of the subVI helps make the code more modular and scalable. NI has posted guidelines for creating FPGA based functions (IP) for reuse.
Here's and example for how you could implement this period measurement VI in a way that is more scalable.
SUB-VI TOP-LEVEL VI
Cheers,
Message Edited by Spex on 11-17-2008 10:47 PM
Message Edited by Spex on 11-17-2008 10:53 PM
Message Edited by Spex on 11-17-2008 10:53 PM
Spex
National Instruments
To the pessimist, the glass is half empty; to the optimist, the glass is half full; to the engineer, the glass is twice as big as it needs to be...
Attachments:
period measurement.jpg ‏48 KB
Period Measurement.vi ‏18 KB
10 period measurements.jpg ‏71 KB

Point-by-p​oint Frequency Measuremen​t

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Point-by-point Frequency Measurement