Accurate frequency measurement using PXI 5142 Digitizer

I am Using PXI 5142 Digitizer to read the frequency of a 10 MHz atomic clock up to 8 decimal places. I am using single tone measurement block. But I can't get that accurate fix on the frequency because of the jitter.
Can someone help.
Thanks in Advance.

Thanks For your reply; The device is connected to the digitizer through BNC connector.
Digitzer Scope Settings:
Samples/seconds --> 2G S/s
Record Length      --> 800
Aqiusition mode   ---> N Samples
Best Regards,
Helal
Attachments:
Block Diagram.JPG ‏117 KB
Front Panel.JPG ‏91 KB

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Frequency measurement using Labview 8 and Fieldpoint FP-CTR-502 - wind speed measure

All the information regarding this kind of application seems to be outdated, I did not find no solution or example to construct frequency measurement VIs using Labview 8
The examples at "NI Discussion Forums :
Most Active Hardware Boards :
FieldPoint Family :
Low-Frequency measurements using counter/timer" is very strange and so far the steps given seems to be usefull only do old Fieldpoint Explorer.
I was trying to find a way to learn how to make an anemometer send its signal to a FP-CTR-502 but I have no sucess.
I am realy very new on this Labview stuff, any help would be welcome.

(similar thread here)
Message Edité par Mathieu R. le 12-23-2005 02:28 PM
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Mathieu R.
  CTD - Certified TestStand Developer / Développeur TestStand Certifié
  CLAD - Certified LabVIEW Associate Developer

Multiple data acquisition using PXI-5124 digitizer

I have a system in which I do data acquisition of the present state of the physical system (using PXI-5124 digitizer),
give the system some change (using labview program itself) and do data data acquisition again corresponding to
the changed state of the system.
So I need to do two data acquisitions in one loop. How do I do this ? Labview examples have some programs (attached file) that
does one data acquisition in one loop but I need to do two.
I tried to make some changes to this program but it doesn't seem to work well.
Thanks
Attachments:
PXI5124-data-acquisition.vi ‏46 KB

From the explanation you have given about reconfiguring the digitizer,
I think the example you are looking at is the one you want.
The digitizer is reconfigured with new settings every time with in that loop,
so the user can change the settings such as triggers and vertical range on the fly.
The original state of the example showed how it was reconfiguring the digitizer,
was there something else you wanted to add to that example?

DAQ frequency measurement using anolog input channel

Hello,
I try to develop a DAQ application which run on a real time target.
I want to measure frequency using anolo inpur channel of my DAQ card. I have a problem.
Let me first try to explain what i trying to do. In the first loop i do sampling and show the result as double array.
I need to show samples as double array so i can not read sample as waveform. With a shared variable i sent these samples to second loop.
First loop reriod is msec and second loops period is 20 msec.So when the second loop run, 20 samples were alraady ready, frequency measurement is done.
The problem is that i need to show frequency measurement as far as possible. Say frequency of my signal is about 100 hz, then this
configuration gives correct frequency measurement. But if frequency of the signal is about 10 hz, this configuration fails since period of second loop is 10 msec and it is not enough time to measure a 10 hz signal. But if i adjust period of the second loop as 100msec,
then i can measure 10 hz signal but then i can give measurement of a 100 hz signal +90msec late. What can i do so i can measure frequency af signals ranges 0-100hz and give measurement result as far as possible?
Attachments:
measure_amp_freq.GIF ‏35 KB

eesen,
What you are doing doesn't make any sense to me. First of all, you should take multiple samples with the DAQmx Read and not one sample at time with the timed loop. Your frequency measurement will then actually be more accurate. You also should return a waveform. That includes timing information that the Freq & Amp function needs to determine the frequency. It cannot do it with a dbl array. If you have to display a dbl, then just use the Get Waveform Components to extract the y array. You can get rid of the second timed loop and use a regular loop for the DAQmx Read. If you just set the rate to be twice the highest input frequency and acquire enough samples for a couple of cycles, you should have a pretty accurate reading.

How to use a photogate for frequency measurement using a NI USB-6211

Hello, I am extremely new to LabView and am having trouble using the counter feature (or if this is even what I should be doing). I am trying to use a photogate as a frequency counter when a voltage spike is created by blocking the sensor. This will then be put into RPM and used to evaluate a small motor dyno I am creating. If anyone has any help or previous vi's they dont mind sharing it would be greatly appreciated. The photogate specifications are for an optek opb930l55. Thanks

Configuring a counter input task will be a little different depending on the type of DAQ card that you are using to read the digital pulses. You just need to wire the voltage from the photogate to one of the counter pins on the card. Then follow one of the many examples for measuring the frequency of pulses. If your card allows it, I would suggest choosing the Counter Input >> Frequency measurement from the DAQmx Create Channel VI. If you have questions about how to do this with your specific DAQ device, please provide more information
Zach C.
Field Engineer
Greater Los Angeles

Low-Frequency measurements using counter/timer

I am trying to measure speed, and am using the FP-502 counter timer module to count the pulses from my sensor. The field point example that uses a fixed width gate pulse will not work for my appliation because I need a gate pulse so big that it updates way to slow.
Does anybody have any sugestions on how to measure a low frequency signal using a counter/timer?
Thanks
Dan

Hello guys
Thanks for all your sugestions I have the final results. I got it to work but I would like to add some comments for anybody who is trying to attempt this.
Triggeing on the gate is a must for low frequency measurements. I used the divide by sugestion however using a factor of 3 only gets you about 60 Hz after that you can't sample fast enough. My application required me to measure from 0 to 150 Hz. I added a "gear shifter" routine where the terminal count was set to 3 on frequencies lower then 45 Hz and 15 for frequiencies greater than 45 Hz. Using a terminal count of 15 for all measurements made the udate rate on really low frequencies way to slow i.e. .5 seconds for 20Hz (check the math on this).
I a
lso needed to cascade the counters. At low frequencies the count went higher than 6550. Using the previos channel function of the fieldpoint module enable me to get 32 bit worth of terminal count data.
Finally I needed to add a timeout condition for 0 Hz. If there are no pulses coming from the senser the program displays the last value read. That won't be 0. So I added a time out routine that if I didn't see a pule in a certian amout of time, output 0 and reset the gate count.
Thank you for you help you relly saved me. I hope my comments made sense.
Dan

Frequency measurement with High Speed Digitizer using External Trigger

Hello:
I

Hello;
That is happening because you are doing Software timed operation, and since Windows manages all tasks that runs on the machine at any given time, your VI might take different times to execute, and that might be enough for you to miss some pulses.
The best way to do that is by using a 660x board, and have three counters doing the job. The firts counter can be configured as the first pulse train generator, the second counter can be used to generate a pulse that will trigger the third counter of. That pulse will be generated when the delay of 90 degrees is reached. So, the second counter will count events and will be triggered of by the pulse train generated by the first counter.
The third counter is configured as triggered pulse train generator, and t
he output pulse of the second counter is used as the trigger pulse for the third counter.
If you don't use that approach, you won't be able to reach fast speeds and might also miss some pulses, due to the Software timed approach.
Hope this helps.
Filipe A.
Applicaions Engineer
National Instruments

Low Frequency Measurements using counter timers

I am trying to measure multiple speeds using FP-CTR-502 modules. I am having a resolution problem. Looking at the post at the following URL (http://forums.ni.com/ni/board/message?board.id=110&message.id=3601&query.id=42252#M3601) looks like exactly what I need to do, but I'm not sure how to program this. Does anyone have any example code to get me headed in the right direction?

Hi Tcrower,
Here is the example that Carl L. was describing in his forum post along with his instructions. Also, there are thorough instructions for using the program in the front panel as well as in File >> VI Properties >> Documentation.
You can measure frequency in two ways using a counter.
1) Measure the time it takes for a set number of pulses to pass or,
2) Count the number of pulses that pass in a set amount of time.
For low-frequency signals it is best to measure the time duration of a set number of pulses. If we tried to calculate the number of pulses that passed in a set amount of time, we would need a long gate period to get accurate results.
The drawback of measuring the amount of time it takes for a set number of pulses to pass is that the sample period varies with the frequency of the signal.
To accurately measure low frequencies with a CTR module, select two counter channels, one output channel, and one gate input channel. Count Input 0 counts the pulses of the signal that we are measuring. The output of the counter is set to high for x pulses and low for x pulses, which is used as the gate of Count Input 1. The source of Count Input 1 is the internal clock reference (the example can be modified to use an external clock reference). During the high phase of Count Input 0, Count Input 1 counts the pulses of the clock reference.
During the low phase, we read channel 1 and reset the counter.
For example, if the output of Count Input 0 is set to high for 4 pulses and the signal has a frequency of 20 Hz, the output of Count Input 0 is high for 200 ms. During the high phase, we will count 200 counts if we are using the 1 kHz internal clock reference. So to calculate the frequency, we have F = #pulses/duration = timebase * terminal count/counts = 1000 Hz * 4 terminal counts/200 counts = 20 Hz.
Regards,
Hal L.
Attachments:
Low_Frequency_Measurement_(CTR).zip ‏77 KB

Frequency measurement using multisim

Hi all
i'm new to multisim and i want to ask about how can we measure frequency of analog signal(ecg) using multisim oscilloscope
I will be waiting for you reply
thnx

Hi Rahul,
OK, for a bandpass filter, you should use the AC Analysis under the Simulate menu. Another method is to drag a Bode Plotter and connect it to your circuit.
For the AC Analysis of the filter respnse, this following link might help you.
Configuring an AC Analysis in Multisim
http://www.ni.com/white-paper/12690/en/
NI Multisim: AC Analysis frequency response
http://www.youtube.com/watch?v=tgCPDBtRcso
If using the Bode Plotter,
MultiSim Bode Plotter
http://www.circuitsmadeeasy.com/index.php?option=com_content&task=view&id=105&Itemid=74
Regards,
Chen_T
National Instruments
Attachments:
14Pin_Chip.ms13 ‏87 KB

Frequency Measurment using Compact DAQ Chassis PFI Input

I have an 8-slot compactDAQ chassis, cDAQ-9178.
I am using Windows/CVI version 8.5 with DAQmx version 9.3 drivers.
I would like to use one of the PFI channels that are provided on this chassis [0/1] to measure a TTL level signal whose frequency is approximately 1KHZ. When I try re-routing or specifiying the PFI channel, using DAQmx functions, as the counter source DAQmx reports a resource conflict.
Can this be done?
According to MAX 4.8 it appears that the PFI0/1 signals can be routed to any of the STPC3 counter inputs. What functions do I use to accomplich this?
Solved!
Go to Solution.

Hi Rgulbrandson,
The counter frequency input terminal is set by a task-based route. To control the source of that route, call DAQmxSetCIFreqTerm(myTask, "", "/cDAQ1/PFI0") before committing/starting the task. Immediate routing functions like DAQmxConnectTerms() can't override task-based input routes, which might have caused the resource conflict you saw. However, without seeing the actual error message I can only guess. If DAQmxSetCIFreqTerm() doesn't help, could you post the error message and a snippet of your code?
Brad
Brad Keryan
NI R&D

Simultaneous frequency measuring

I have to measure for frequency signals simultaneously, so that I'm able to associate one measured value to the others. How do I synchronize this? Is this possible with the four counters on a 6601 board? Two of the signals have frequencies up to 15 KHz, two of them go up around 4kHz. I also have a 6014 board with an additional counter available, maybe I could use it somehow...I also have to synchronize the analog acquisition that I perform with the 6014 with the one of the frequency signals, namely a continuous TTL pulse.
Thanks in advance for any help!

Hi Achim,
Typically, frequency measurements are made using two counters for increased accuracy. However, you can measure frequency using 1 counter and taking the inverse of the period measurement. You would just need to apply this to 4 counters. There should be a shipping example with the NI-DAQ driver that performs this. Here is a link to an excellent tutorial on frequency measurement.
Making Accurate Frequency Measurements
http://zone.ni.com/devzone/conceptd.nsf/webmain/CD2C8AAED8FA59A486256C230078FE75?opendocument
This being said, what I suggest in your case is to use a 6602 counter/timer board with 8 counters, 2 for each frequency measurement. Using a 660x board, you can also use triggering to simultaneously start all counters. This can be
done by routing a signal from the PFI line to the counter trigger using Route Signal.vi in LabVIEW or Select_Signal() in C function calls. Then you would setup a trigger and reference the common trigger signal that you routed the PFI line to. The following discussion thread might be useful:
Counter/Timer Triggering 660x
http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RNAME=ViewQuestion&HOID=506500000008000000B2300000&ECategory=Measurement+Hardware.Counter%2FTimer
Anyway, I hope that helps. Have a good day.
Ron

Frequency response measurements with pxi-5922

I’ am using signal express and the pxi-5922 digitizer together with the AWG pxi-5441 to analyse the frequency response of a buffer amplifier. See the attached signal express file. Many different ways to measure the frequency response have been tried and this is the best I came up with. It is basically two tone extract steps in a sweep loop. But I’ am still uncertain if this is the best way to do this kind of measurement. The fact that the detected frequency differs between the two channels worries me, even when the two channels of the pxi-5922 are looped. Is there a more accurate way to determine the frequency response?
Best wishes
Stefan Johansson, SP
Attachments:
sweep.JPG ‏397 KB
Frequency Sweep funkar.seproj ‏81 KB

Claudia-
Thanks for the response.
Regarding the CJC- When I switch it on, the temperature readings I get are very random, roughly negative 1 degrees. (I am operating right now at room temperature, and will be using J-type TC's to measure ~43 degrees C). Also, when I use the built-in CJC, the aquisition rate seems to slow down considerably. When I use the "user specified" everything seems to be ok, including the aquisition rate.
I measured the resitance of the Thermistor on the TBX-68T and it was about 5000 Ohms, as expected.
Just to make sure: When using the TBX-68T, do I need to hard-wire a thermocouple to Channel 1/auto-zero and another to channel 0/CJC? Because I connected a TC to channel 0 right now, but I wasn't 100%
sure.
I've attached my main vi and two sub vi's that I am using for the voltage aquisition part of my project. (Note:the current measurements are just voltage measurements multiplied by the recipricol of the resistance it was measured across, ie. 10).
I would like to keep this file as is because it writes to a file exactly the way I want it to. I'd like to have the temperature aquisition with the 4351 in the same vi as the 6030E so that they both stop and start at the same time. I am just not sure how and where to log the temperature data since there will be fewer data points than the voltage data. Any suggestions? Should I write two separate files? can I somehow append them?
Thanks again. Hope to here from you soon.
Attachments:
EBlackMainDAQ.vi ‏107 KB
Save_Data8.vi ‏45 KB
Build_String_Array5.vi ‏33 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

Sampling frequency when using USB6251 for SemiPeriod measurement

Hi there.
I am using the USB-6251 for frequency measurement. I use C# and the latest 8.5 drivers for .Net 3.5.
My question is this:
I have CounterInputChannel with MeasurementType=SemiPeriod.
The TimeBaseSource is "80MHzTImebase" and Prescaler is 1.
The reported minimum (CICHannel.Minimum property) is 25ns - 40MHz
I am measuring frequency on a 32.768kHz crystal which should be pretty stable and accurate. The measurements suggest that the samplerate is actually 20MHz, not 40MHz. This also makes sense, because if I try to create a frequency measurement, I am forced to use a divisor of 4 or more - which gives a sampling rate of 20MHz.
So my question is this: Is the reported minimum as read from CIChannel.Miminum wrong?

Additional info,
I downloaded and ran the DAQ diagnostic Utility v1.0 and got the following results, see below
Regards,
runson
9/16/2005 6:54:58 PM
Results saved to: C:\Documents and Settings\Runson\My Documents\Diagnostic Results.txt
Selected Device: Dev1
Device Type: PCI-6250
Serial Number: DE4115
Device Support: (PASS)
NI-DAQmx Version: 7.5 (PASS)
Device Reset: (PASS)
The device was last self-calibrated on: 9/15/2004 5:04:09 PM
Running Calibration ...   (PASS)
-------------------- Testing Counters... --------------------
Testing CTR Buffered Pulse Generation...   (PASS)
Testing CTR Single Pulse Generation...   (PASS)
-------------------- Testing Analog Input... --------------------
Testing AI Ground Reference...   (PASS)
Testing AI Voltage Reference...   (PASS)
Testing AI Finite Sample Clock...   (PASS)
Testing AI Finite Sample Clock Frequency...   (PASS)
-------------------- Testing Digital IO... --------------------
Testing DIO Lines...   (PASS)
Testing DIO Ports...   (PASS)
----- DIAGNOSTIC TEST COMPLETE -----

6602: How to use 8 counters simultaneously in C++ using traditional Daq for frequency measurement

Hi Everybody;
I'm new to Ni-DAQ cards and working on NI PCI-6602 Card in Borland C++, I should use Traditional DAQ for my project. Now I want to use all the 8 counters simultaneously for frequency measurement.
1.Where should I connect my External signal, to source or gate, at present I have connected to source.
2. How to set parameters and start the counters simultaneously, what are the parameters to be set for frequency measurement.
3.How to start counting.(parameter settings)
4.Should I set any PFI Lines or by default are they set to counters.
status = GPCTR_Set_Application (1, gpctrNum, ND_SIMPLE_EVENT_CNT)
status = GPCTR_Change_Parameter (1, gpctrNum, paramID, paramValue)
iStatus = GPCTR_Watch(1, gpctrNum, ND_ARMED, entityValue);
status = GPCTR_Watch (deviceNumber, gpctrNum,ND_COUNT, entityValue)
what is the paramID in my case, Clear and appropriate answers would be very helpful and thanks in advance.
Message Edited by Pavan K on 07-11-2009 12:38 AM

I have made a program with LabVIEW 5.1 based on NI 6602, in which four counters were used.
Counter 3 is used to generate pulses, which are directed to the gates of counter 0, 1 and 2.
The source terminals of counter 0,1 and 2 receive pulses, individually, to count how many pulses appear during the time interval of each gate pulse.
The results are stored in a data file.
In order to test its performance, only one signal of ramdom pulses is sent to counter 0,1 and 2.
But I find that at the beginning the counts for the three counters are the same, but the following counts are totally different!
What's wrong? And how to solve such a problem? Does it have something related with synchronization?
Thank you very much!

Accurate frequency measurement using PXI 5142 Digitizer

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