High frequency measurement

I need to measure a frequency around 3 Mhz the signal is in bursts.
I have the example 2 counter.vi working with a siggen with a continuous output but can't get a reading on the burst.
Below is the vi and scope shots of the signal I need to measure.
Attachments:
DAQ Counter.png ‏41 KB
freq1.png ‏46 KB
freq2.png ‏44 KB

johnsold wrote:
I suspect that the best way for you to measure the freqeucny of the bursts is to use an analog acquisition with a sampling rate of at least 10 MHz (higher is probably better). Then do an FFT on each burst. The images you posted earlier show about 30 cycles in a burst. That is enough to get a reasonable response from an FFT. You could also detect zero crossings and calculate the frequency from that. FFT may be easier.
Does the frequency vary within a burst? Does it vary from one burst to the next? What is the range of frequencies in the bursts? What frequency resolution do you need? How fast do you need to analyze the data? Between bursts or seconds later?
Lynn
The frequency is constant in each burst and is the the same from one burst to the next.
Resolution does does not need to be real acurate .5 mhz would work, but the more acurate the better..
I have lots of time to analyze the data at least 30 seconds to capture and analyze.

Similar Messages

High frequency measurement 2 counters range

Hello,
I know this info is somewhere but I can't find it.
When using a Counter/timer to measure frequency there are multiple methods.
i.e. Low Frequency with 1 counter and high frequency with 2 counters.
What is the definition of a "low frequency" and what is the definition of a "high frequency"? i.e. low frequency = frequencies below 100 Hz
Also what is the definition of a "large range"?
Thanks
Dan

Hi Dan
There isn't a specific bandwidth that is defined for use with either the one-counter or two-counter method. However, located in the NI-DAQmx help file there is a section detailing the quantization errors that arise when using either method with a variety of input frequencies. By referring to this information you should be able to determine which method will produce the smallest error in your application and hence which method will be preferable. This help file also explains the errors associated with the large-range two-counter method.
To locate the help file, you should select Start»All Programs»National Instruments»NI-DAQ»NI-DAQmx Help, and search for 'quantization error'.
I hope this helps, just let me know if you'd like anything clarified or if you have any other questions on the matter.
Regards
Jeremy T
Technical Marketing Engineer
National Instruments UK & Ireland

New M Series DDK Example: High Frequency Measurement with 2 Counters

This example demonstrates how to configure two counters on an M Series device to measure a high digital frequency. One counter generates a continuous pulse train of a set frequency while the other counts the external signal using the pulse train to latch values. Data is transferred via DMA.
Use this example to add high digital frequency measurements or DMA data transfer for counter input to your driver.
Please let me know if you have questions or problems. Thanks :-)
Joe Friedchicken
NI VirtualBench Application Software
Get with your fellow hardware users :: [ NI's VirtualBench User Group ]
Get with your fellow OS users :: [ NI's Linux User Group ] [ NI's OS X User Group ]
Get with your fellow developers :: [ NI's DAQmx Base User Group ] [ NI's DDK User Group ]
Senior Software Engineer :: Multifunction Instruments Applications Group
Software Engineer :: Measurements RLP Group (until Mar 2014)
Applications Engineer :: High Speed Product Group (until Sep 2008)
Attachments:
gpctex5.cpp.gz ‏4 KB

You should connect the signal (whose frequency needs to be measured) to Ctr-1, and there gonna be an internal connection between the output of the first counter and the gate of the second counter (as described here).
You may want to check this link as well.
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Make your LabVIEW experience more CONVENIENT.

DAQmx Error 89137 When trying to make a high frequency measurement.

I am using a PCI-6602 Timer/Counter for multiple measurements on a serial interface...
I have the clock line connected to Gate0, the enable line to Aux0 because I need to make a two-Edge seperation measurement between the two later...
But I also want to make a "Period/Frequency Measurement (High Frequency with Two Counters)" measurement...
This requires that the signal to be measured is on Source0...
I implimented the following Code:
void meas_FP_Freq(float64 *Freq0, float64 *Freq1)
TaskHandle CLK0_Freq, CLK1_Freq;
DAQmxCreateTask ("FP_CLK0_Freq", &CLK0_Freq);
DAQmxCreateTask ("FP_CLK1_Freq", &CLK1_Freq);
DAQmxConnectTerms ("/Dev3/PFI38", "/Dev3/Ctr0Source", DAQmx_Val_DoNotInvertPolarity); // Gate0 to Source0, No Error....
DAQmxConnectTerms ("/Dev3/80MHzTimebase", "/Dev3/Ctr1Source", DAQmx_Val_DoNotInvertPolarity);
DAQmxCreateCIFreqChan (CLK0_Freq, "Dev3/ctr0", "", 6000000, 6500000, DAQmx_Val_Hz, DAQmx_Val_Rising, DAQmx_Val_HighFreq2Ctr, 0.001, 4, ""); // High freq measurement
DAQmxCreateCIFreqChan (CLK1_Freq, "Dev3/ctr1", "", 6000000, 6500000, DAQmx_Val_Hz, DAQmx_Val_Rising, DAQmx_Val_LowFreq1Ctr, 0.001, 4, "");
DAQmxReadCounterScalarF64 (CLK0_Freq, 3.0, Freq0, 0); // Run-Time Error -89137 Specified Route cannot be satisfied..etc
DAQmxReadCounterScalarF64 (CLK1_Freq, 3.0, Freq1, 0);
DAQmxDisconnectTerms ("/Dev3/80MHzTimebase", "/Dev3/Ctr0Source");
DAQmxDisconnectTerms ("/Dev3/80MHzTimebase", "/Dev3/Ctr1Source");
DAQmxClearTask (CLK0_Freq);
DAQmxClearTask (CLK1_Freq);
The "Low Frequency" method works fine, but the resolution is too low...
Every help file I've read indicates I can use different PFI inputs for measurements... What am I missing?

Hi,
The reason that you are getting the error is the PFI lines are being reserved twice. You don't need the DAQmx Connect Terms functions in your code because the DAQmx driver does this for you automatically. If you still receive an error after doing this, try to changing the low frequency counter number. I hope this helps you with your application.
Regards,
Hal L.

High frequency power measurements

Hey,
I'd like to know if there are developments in measuring electrical high frequency signals with labview without using an extern power analyser. At the moment i'm using a yokogawa power analyser but i'd like to know if it's possible to log HF signals without the help of a power analyser... Are there NI products on the market for this purpose?
Thx,
Andy

Hello,
In the case of frequencies up to 200 KHz, NI can provide several solutions using the 'standard' data-acquisition boards or digitizers (scopes), from a low to very high accuracy solutions.
A good solution can be one of the high speed M-series boards (PCI-625x). These boards have up to 32 multiplexed channels with a resolutions of 16-bit at a speed of 1 MS/s (500 KHz).
A better solution would be a S-series boards. These data-acquisition boards sample all input channels simultaneously. We have boards with 2, 4 and 8 channels and sample frequencies of 10 MS/s (up to 5 MHz if needed). S-series board are the boards with product numbers PCI-61xx.
The best solution is to use a digitizer (scope). Also here a lot of possibilities going from low to higher bandwidth and resolution.
The most flexible is the PXI-5922. A 24-bit digitizer if you sample @ maximum 500 KS/s. This board only exist in the PXI platform.
Then NI has 8-bit digitizers (normal resolution for scopes) from 15 till 125 MHz bandwidth. If you need a higher resolution they have solution up to 14-bit (very high for scopes) @ 100 MHz.
Please give your local NI Office a phone call.
They have technical engineers who can discuss your needs and provide you a solution.
Best regards,
Joeri
National Instruments
Applications Engineering
http://www.ni.com/ask
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Continuous frequency measurement~

Dear sir,
    How are you today?
    I tried to program the "Measure Frequency.vi" in LabView 5.1 . I've the simplified version
from "LabView Measurements Manual" in page 10-26. Basically, we want to measure the
frequency change within 20 ms (chirp). So I just naively added the "for loop" enclosing everything,
as the attached VI. But the testing result (please see the attached document) showed that
sometimes the counter/timer (AM9513) lost count. Could you please troubleshoot my VI and
tell me how I should improve?
    In addition, I tried to use the oscilloscope to see the gate signal from counter-1 (counter 5)
OUT pin, but it showed 0.14V. The signal from GATE pin of counter (counter 1) showed 5V.
I was expecting what I would see is something like TTL signals with different pulse widths and
delay widths. Can you tell me what I was doing wrong?
    Thank you for your previous answers!
Best regards,
Margaret
Attachments:
Continuous Measure Frequency1.1.vi ‏122 KB
continuous frequency measurement.doc ‏168 KB

Hi Margaret,
I think that there is one way to obtain a count every 20ms. What you will need to do is:
1. Generate a 50 Hz pulse train
2. Connect your signal to the a counter source
3. Connect the 50 Hz pulse train to the counter gate
4. You will obtain a series of counts over a 20ms period and you will be able to determine the frequency of the signal using post processing by dividing the count # by 0.02.
I noticed that you are using LabVIEW 5.1. This version of LabVIEW is no longer supported. I highly recommend upgrading to a newer version of LabVIEW. This will allow you to program with the DAQmx driver and creating your application with this driver would be significantly simpler and take a lot less time.
If you do not want to try this method, then I am attaching the screenshot for measuring the time the while loop takes to execute. I want you to know that the overall time will not have an effect measuring the signal's frequency. There really isn't anything you can do to decrease the execution time for the counter. I hope that you find this information helpful.
Regards,
Hal L.
Attachments:
While Loop Timing.gif ‏12 KB

PXI-6624 Pulse Frequency measurement

Hi. I'm working with a PXI-6624 and am interested in doing pulse frequency measurements to get both frequency and duty cycle on its inputs using DAQmx.
Whenever I go to create the virtual channel however, I get error -200431:
"Selected physical channel does not support the measurement type required by the virtual channel you are creating."
"Requested Value: Pulse Frequency"
"You Can Select: Frequency, Period, Pulse Width, Semi Period, Two Edge Seperation, Position:..."
Is this card really not capable of doing these pulse frequency measurements?
Solved!
Go to Solution.

Yes, the "Pulse" (not to be confused with "Pulse Width") measurement was introduced with NI's STC3 devices including X Series and CompactDAQ.
Pulse Measurement:
However, you should still be able to measure frequency and duty cycle on your card with a semi-period measurement:
Semi-Period Measurement:
Images are from the X Series User Manual.
The difference between the two modes comes down to how the data is stored and buffered on the card--with the semi-period method the hardware doesn't distinguish between high and low samples and puts everything into a single buffer. However, if you start the counter off the appropriate edge (see below property node), then you would know in software the order of high and low samples and can pretty easily calculate frequency and duty cycle from this.
Best Regards,
John Passiak

FP-CTR-500 and Frequency Measurement: How to modify it to report the frequency (0-10 Hz) every one minute?

How to modify "Frequency Measurement" to report the frequency every one minute?
The signal frequencies vary from 0 to 10 Hz (see the analog output plot and attached sample data file), so I want record the average frequency every one minute.
Software: Labview 8.5
Hardware: FP-CTR-500
Program: "Frequency Measurement" --build in and under "NI example finder", It was attached with this message.
Physical wiring: (1) The signal I want to measure to count input 1 (pins 2 and 18). it is a pulse signal (range from 0 to 1 V, see the plot and attached data file).
(2) Wire Output 0 (pin 130 to gate 0 (pin 9). Do com pins 26 and 30 need to wire together?
FP-CTR-5000 was set up in Max based on the program instructions. I have tried different gating pulse frequency, my readings are always "0".
Attachments:
H2O_20130809.xlsx ‏18 KB
Frequency Measurement.vi ‏35 KB

CTR-500 high pulse is >=10V. Hence, it always read your pulse as low. With this low voltage pulse, you must use analog input module, and write a program to read pulse from analog level. You must also make sure that you pulse is not so narrow that cFP loop is not fast enough to capture voltage change.

High frequency quadrature decoder (NI PCI 6221)

Hello, i would like to ask you about high frequency quadrature decoder. I am using module in DAQmx for measuring linear position. For this i am using NI PCI 6221. My problem is that i want to use this for my interferometer and we need really high speed. So I tried to use External timing whitch should be possible for this card up to 80MHz. Unfortunatelly i always will get error message that there is some kind of owerflow and my program crashes. So my question is how to get all data form this card. I know that the buffer size FIFO is only 2 so if it is impossible to get all data so i want find another solution. Is it possible let my card work alone on 80MHz and only repeatly rewrite all buffer and just sometime ask this card for sending current buffer. I dont really need all the data, but when i will ask i need to know reall position. This high speed is really necessary because my interferometer is sensitive and i dont wat to lose any steps. If there would be any possibility how to work on 80MHz and only sometime ask for sending data with position, it would be great. Sometimes i will ask not for only current position but for full buffer because i want so see what is happening during some time period, but this task will be only sometime.

Dear BMAJTZ,
The counter frequency (the maximum speed available) is configured by the Task in the background. In our case, the counter is set to detect edges, so it always uses the maximum speed available. If an edge occurs, the count value increases by 1, and this accumulated count value (stored as a binary number) is read by the DAQmx Read VI, and converted to meters. So if your encoder input is slow enough for the 80 MHz card to handle, you won't miss any ticks, even if you only read the value occasionally.
You can find further information about counters and encoders on these links:
http://www.ni.com/academic/students/learnlabview/digital.htm
http://www.ni.com/white-paper/7109/en
Also if you can tell me the approximate frequency of your encoder signal, and how often you nedd the position info, I can do some benchmarking for you to see if your card is capable of the task.
Best regards:
Andrew Valko
National Instruments
Andrew Valko
National Instruments Hungary

NI9411 wrong frequency measurement of flow sensors / 24 impulse signals

Hello Ni Forum,
I already searched for similar problems, but haven't found anything helpful. So I'm posting our problem here. I'm apologizing in advance for bad english, it's not my mother tongue
We're encountering some strange behaviour of our NI9411 Module. We're using it in a Compact Rio with some other modules (2x Analog In).
Our goal is to measure the frequency of three flow sensors (impulse high = 24V, 0-22kHz) among with a torque sensor (TTL 5V, 30-60kHz) and a speed sensor (TTL 5V, 0-51,2kHz).
They are wired as follows:
DI0a = torque sensor
DI1a = flow sensor 1
DI2a = speed sensor channel A
DI3a = speed sensor channel B
DI4a = flow sensor 2
DI5a = flow sensor 3
Correspondig ports b are left unconnected, as it is said in the data sheet. All ground ports of sensors are connected to COM port of 9411. The module was connected to a 24V power supply.
Now the torque and speed sensor measurement works fine. But measuring the signals of the flow sensors seems to be difficult.
If an external frequency generator (impulse high about 9V, f=1,000kHz) is connected to port DI1a instead of the sensor signal, LabView shows exactly 1,000kHz. DI5a showed an avarage of 10 Hz, with a range from 10 to 60 Hz. DI4a equaled constant zero. The flickering up to 60Hz of DI5a was gone after disconnecting the 24V supply of the module. This changed nothing on the phenomenon described below.
If the signal high impulse voltage is raised, the measured signal frequency goes up to 1300 Hz @ 24V signal high impulse voltage. The signal additionally raises, if an oscilloscope is connected to DI1a, to 2180 Hz (range 2110 to 2240Hz). However, there is no change of frequency if the osci is connected to DI5a. With the 24V supply connected, DI5a showed a frequency up to 600Hz @ 24V signal high impulse voltage on DI1a, also rising when connecting the osci on DI1a. As mentioned, there was no frequency measured on DI5a after disconnecting the 24V power supply.
The signals of the generator showed some peaks on each edge (rising and falling) with values for example of 11V above high impuls voltage of 9V (20V together). That may causes that wrong frequency measurement.
The signals of the flow sensors do not have such peaks, the LabView-frequency nevertheless does not match the real frequency, as shown below (all values in Hz):
LabView
ideal values
Flow Sensor 1
Flow Sensor 2
Flow Sensor 1
Flow Sensor 2
4600
12200
740,6
6760,0
6400
13500
1481,3
7500,7
9700
16400
2962,6
8982,0
12900
19500
4443,8
10463,2
We're kind of helpless now. How can we get the signals of the flow sensors measured the right way? Are we doing something essentially wrong? Thanks in advance for offered help. I hope, I've given any necessary information. Any missing details will of course be delivered.
Puls-Measure-VI is attached beneath.
Regards,
Johannes Rost
Attachments:
vi.png ‏20 KB

Dear Lynn,
thank you for your reply. The impedance was an issue that our local technical distributor already suggested to check. According to the datasheet of the flow sensor (see attachement) it can drive a current of 25mA. The signal generator we used is a test generator that can be used instead of the flow sensors to check the any evaluation unit the sensor is connected with. So it should generate signals that are equal to those the sensor would have generated. And even with this the frequencies measured with LabVIEW are not as expected.
We are in contact with the sensor manufacturer to exclude mistakes in connection on the sensor side. But the behavior with the signal generator makes us think that is has to do something with the characteristics of the NI9411 that we don't know yet.
Attachments:
block diagram signal amplifier and signal description.png ‏151 KB
technical data.png ‏124 KB

Why does my AI acquisition slow down to my frequency measurement rate?

I'm using Labview/Daqmx to program my SCXI 1520 and TC modules while at the same time using the multifunction capabilities of the E-card controlling the SCXI. This has been fairly easy until I wanted to use the frequency and counter measurements (outputs/DIO works great). I'm using a waveform with buffered acquisition for the read on the AI channels and obviously there is no waveform for the frequency measurement so I'm just combining the signals using the dynamic data. This works great when my input frequency is higher than my acquisition frequency. When my input frequency is lower than my acquisition frequency the acquisition slows down to that frequency and the AI read falls behind (buffer fills while waiting for another frequency measurement). I'm assuming the frequency read is not keeping up with AI read. I understand that as the frequency is reduced it takes more time to calculate the frequency. So how do I "read" the frequency measurement at the same rate as the AI data? I'm fine with using the last frequency measurement until a new frequency measurement is available but I can't even seem to be able to do that.
An example of the problem is measurement of vehicle pedal force (AI channel) with pulse input for vehicle speed. Assuming 100 Hz acquisition and the vehicle stopped or going slow (very slow pulse train) I should be able to acquire data at 100 Hz even if I just use the last data point for the frequency channel until another point is available.
Please help, thanks.

Basically, the very fact that you're *doing* a frequency read suggests that you don't know the expected freq ahead of time, and probably suggests that it can vary. The waveform datatype assumes a constant interval between samples which wouldn't generally be true for frequency measurement, and that's why you can't use it. Since the actual timestamps of the frequency measurements are NOT the same as those in the analog waveform, it's likely a mistake to pretend they are.
My method is to create my own array of "timestamps" for the frequency data. Create a For loop with a shift register initialized to 0 from outside the loop. Let your freq array auto-index the loop. On each element, perform (1/x). Add result to the left-hand shift register value and write it to both the right-hand shift register and to an auto-indexing output. When the loop completes, the output array will hold timestamps that correlate to your freq measurements. From there you can choose whether to display on an X-Y Graph, or whether to perform some interpolations to calculate freqs at the analog sample times or vice versa.
-Kevin P.

Bandpass filter amplifies only noise at high frequencies and saturates the opamp output

I have designed a fourth order bandpass filter using the opamps TL081C. It is designed to operate at a center frequency of 40 kHz with a bandwidth of 2 kHz and a gain of -12.5 . I am using an SCB-68 board for data transmission and reception, one channel each for transmitter and receiver. I have grounded the adjacent channels to both the transmitter and the receiver in order to avoid crosstalk. However, at the output, I get a signal which looks like an amplitude modulated signal and is, most probably, noise. The amplitude of this signal is always around 9V, no matter what is the amplitude of the input (even if the input is 0V, the result is the same). If I scale down the whole BPF to operate at a center frequency of around 20 kHz, everything works fine. Therefore, I think the problem lies not in the design of the BPF but the use of the board at higher frequencies. Please reply as soon as possible.

You have done something wrong. You should read the manual for both the SCB-68 and your DAQ card once more. In such cases I often use MAX, and a battery as source. Then a DAQ input is not connected (floating) you will see measurements like you are doing now. Some high level voltage often modulated with mains frequency.
Besides which, my opinion is that Express VIs Carthage must be destroyed deleted
(Sorry no Labview "brag list" so far)

Frequency measurement of a very short pulse

Hi I am using PXIe 6368 to measure Oscilliator Frequency. This signal is connected to PFI lines and I would like to use counters to measure frequency but the pulse width is too brief ( 12 ns ) . How can I determine if the hardware counter can even detect this short pulse for frequency measurement?
Thanks

Gerd,
i am not aware that TTL specifies detailed timing information. The main reason: TTL was introduced as "standard" in 1961. In the mean time, all our semicondictors are way faster than back in that time. So if TTL would specify timing in detail, there would be the requirement for different versions of TTL (just like USB 2.0 vs. USB 3.0).
I don't know about TTL 2.0 (or higher), so i doubt timing specs to include hard numbers.
NI specified TTL signals for older controller chips (compare here) but i am not aware of any updated document for STC3 chips which are used for X-series devices.
Norbert
CEO: What exactly is stopping us from doing this?
Expert: Geometry
Marketing Manager: Just ignore it.

NI Mydaq gain loss at Higher frequencies

Hi There,
I am using a MYdaq for my student project, I am using this is an audio sine wave generator and analysis tool as part of the project.
I am sampling well above nyquist of my highest frequency (20K) at 100K sample rate both on my OP DAC and IP ADC and I have a buffer size of the same size on the I/P and output.
I am using the audio L/R inputs and outputs (AC coupled) - This is looped fro the purpose of this excercise.
When I generate frequencies (via the Sinewave Vi in labview - "NI_MABase.lvlib: sine waveform.vi" and my FS and #s is both set to 10000.) i get a drop in level above approx 10K starting at about -1dB up to -3dB at 20K
Can anyone help me in tracking down the cause of this?
Regards

Hi,
Just to for my own sanity, have I got these values right?
- Sampling at a frequency of 100kHz. (Analogue Input and Output)
- Intending of sampling a 20kHz signal.
The specifications of the NI myDAQ can be found here. These specify that the device can sample up to 200kS/s for both Analogue Input and Analogue Output, meaning that the maximum clean sinusoid we can both generate and acquire should be 20kHz, with 10S to represent the wave. Higher frequencies will require lower samples and the signals will look more chopped and aliasing will occur (20kHz*10S = 200kS/s). In order to appropriately measure the 20kHz wave, we need to choose a maximum sample frequency of 200kHz for clean waves. With this in mind 100kHz sample rate should be okay.
Is it possible for me to check the code that you have written so far? What I imagine could be happening is that we're seeing these issues due to the slowness of software. If you look at your code and the DAQ VIs are continuously having to check what values to write, rather than having these values delegated down to the hardware layer prior to running the task, this could be the source of the issue. This is because in software, there is a maximum update rate of 1kHz; this is why all of the base clocks in LabVIEW software are 1kHz clocks. If we're constantly having to poll what kind of digital output values we want to write, this will affect the consistency of the generated signals.
Kind Regards,
Alex Thomas, University of Manchester School of EEE LabVIEW Ambassador (CLAD)

Frequency Measurement Algorithm

I'm writing a VI where I need to measure the
frequency of a pulse. This frequency is proportional to a physical measurement,
in this case flow rate. I know how to get the frequency measurement into my VI,
and all is well as long as the frequency is higher than my VI update rate. But
things become more complicated and non-trivial when the frequency drops below
the VI update rate, because during some loops there will be no pulses occurring
since the last loop. In this case I could just assume that the frequency is the
same as last time, and for constant frequencies this works well. But there is
also the case where the flow rate has suddenly stopped, and hence a zero pulse
frequency. If I assume that the last known value is also the current value, my VI will be stuck
reporting the last known flow rate, and will not ever report a zero rate. It
must be the same as a digital frequency to analog converter, but I couldn’t
find information on the algorithms used. Has anyone worked out a solution to
something like this using Labview?

Hi,
I have done something similar before. You mention frequency to analog conversion - that's precisely the principle I used. Basically you count your pulses (cycles, level crossings, etc.) and feed them into an integrator. Mathematically it works like this:
F(0) = 0;
F(i) = [ F(i-1) + N(i)/T ] exp (-t/T);
F(i) - frequency after the i'th iteration
N(i) - number of pulses detected during the i'th iteration
t - iteration time
T - the integrator time constant
For a fixed frequency the estimator output stabilizes at N/t, but if the pulses stop coming, e.g. N=0, the output will decay to 0.
Use smaller T for a more "responsive" frequency estimator, larger T for a more "steady" one.
Hope this helps! Zador.
P.S. Here's a link to a previous discussion on pulse detection:
http://forums.ni.com/ni/board/message?board.id=170&message.id=191867#M191867

High frequency measurement

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