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

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PXI 6229 pulse period measurement

Hi there,
I try to make pulse period measurement using PXI 6229 counter, I have 0.5Vcc according to DMM and 1.05V peak2peak based on scope. Then, I connected 0.5Vcc (incoming pulses) into SCB68 pin 3 and GND pin 55. I used the DAQ assistant to perform measurement n the setting for Signal Input range is min= 1ms and max = 23ms, those values I got it from scope i.e pulse period. I set it to the Rising and Acquisition Mode to 1 sample(on demand). But, I can’t get the measured values and I have no ideal why?
Please help
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Hi Walter,
the counter input of the PXI-6229 accepts standard TTL digital signals. You can find its specifications on page 7 of this document.
I will repeat the relevant parts here:
Input high voltage: Min: 2.2 V; Max: 5.25 V
Input low voltage: Min: 0 V; Max: 0.8 V
If I'm correct, your signal does not meet these specifications, so in this case you will have to connect the signal to an analog input and measure the pulse width as if it was an analog signal.
Please check this page for an example.
Daniel

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?
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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.
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Pulse Generation application with DAQmx and a PXI-6624 module?

What is the best implementation method for the following pulse generation application
using LabVIEW, DAQmx and a PXI-6624 counter\timer module?
I have two rising edge trigger signals (Trigger-1 and Trigger-2).
There is ample spacing between each trigger. They never occur at the same time.
I need to generate a single pulse (fixed width, variable delay) whenever Trigger-1 occurs and
a finite pulse train (fixed width, variable delay, N-pulses) whenever Trigger-2 occurs.
However, the output must appear on one counter output because this composite signal
will be used as a trigger source for another PXI module in the rack.
With DAQmx and a TIO counter\timer can I use both the GATE (for Trigger-1) and
AUX (for Trigger-2) at the same time on the same counter to gate out the desired pulses?
Trigger-1 would be wired to the GATE of CTR0. One Trigger-1 event would generate one pulse on the output of CTR0.
Trigger-2 would be wired to the GATE of CTR1 and the output of CTR1 would be routed to the AUX input of CTR0.
One Trigger-2 event at the GATE of CTR1 would generate multiple pulses on output of CTR0.
Would DAQmx and the PXI-6624 TIO support this implementation?
What is the best way to accomplish the task at hand.
Thank You.
Best Regards,
Scooby

Hi Scooby,
I have looked into the application you have described and I see a potential problem with what you describe. In DAQmx, it is not possible to call the counters of the same DAQ device in the same task, so you cannot have the finite pulse train generation and the single pulse generation tasks running at the same time. What you can do, since you mention the triggers will not occur at the same time, is to stop one counter task while you are triggering another. The way I would suggest you merge the outputs is with a two input Or logic gate to avoid damaging your counters. Your signals will effectively be added together by this logic gate. I do not see any way to merge the outputs internal to the DAQ device.
Please let me know if I can be of additional assistance.
Laura

Measure pulse frequency with 4.7 volt peak amplitude

used two shipped Measurment Studio Vb.Net 2005 Examples:
1-Example 1 : CountDigEvents "MEASURES PULSE COUNTS" and Example 2: MeasDigFrequency_LowFreq1Ctr "MEASURES PULSE FREQUENCY"
2-Example 1 works fine measuring pulse counts , however Example 2 did not recognize pulse frequency , the pulse amplitude voltage is 4.7 volt peak
3-during testing used counter ch0 channle by connecting Sorce0 and Dgnd pins to signal source.
4-using Nidaqmx 9 and MIO-16xe-10 daq
5-pulse frequency around 10 khz
QUESTION:
-please advice what to do to make frequency measures ?
Thanks

Hi MyKat,
Note that the connections are different for edge counting and low frequency frequency measurements with one counter. For the latter, you'll need to connect the signal to PFI 9 rather than PFI8 as you did for edge counting.
http://zone.ni.com/reference/en-XX/help/370466W-01/mxdevconsid/eseriessigcounters/
Regards,
-Jim B
Applications Engineer, National Instruments
CLD, CTD

Low frequency pulse duration measurement

We have low frequncy pulse duration measurement to be done . We have tried with pulse measurement but it shows error for the frequency bellow 1.5 Hz. We have input signal of frequency varie from 0.5hz to 3 hz .Please suggest us is there any other method that can be used for mesureing the pulse width with low frequency mentioned above .If this can be done using tick count , please send us the example .
Regards,
Sharanu

Hello Sharanu,
I'm not sure you will be able to measure a frequency below 1.5 Hz in
the traditional way. However, I would like to ask you some more
questions about your system.
1) What hardware are you using?
2) What is the error you are receiving (please include the exact error text)?
Eric
DE For Life!

Changing the PXI-6624 Counter Output rate on the fly

I'm programming an application in VB.net 2005 to set several counter output channels (each with its own task) on the PXI-6624 card. I'd like to know if there is a way to change the frequency of the output without stopping the task, changing the frequency and restarting the task. I'm using the PXI-6624 card to simulate encoders and speed sensors.
Thank you very much,
JonS101

Hi,
Yes, you can change the frequency on the fly. Here is a knowledgebase that will give you an insight of how you should approach this matter. How Can I Change the Duty Cycle on My Continuous Pulse Train? To find this property node and how to use it refer to the DAQmx .NET reference: Where Can I Find NI-DAQmx Property Node Listings and Help?
I hope it helps
Jaime Hoffiz
National Instruments
Product Expert
Digital Multimeters and LCR Meters

Wiring - PXI-6624

Hi All -
I have an application that I need to make use of a counter, we chose the PXI 6624. I'm pretty darn good with the rest of NI hardware, aside from counters FPGA and RF are the only lines I haven't used. I'm running into some trouble understanding how to set up my leads on the 6624 and thought I'd ask on here.
I have a remote optical sensor (Monarch Instruments Model ROS) that I will need to monitor pulses on. Its got 4 leads coming off of it, a common, a signal, a +V excitation(10V), and the cable shielding (ie common). I'm also hooked up to a SCB-100 using their 100 pin flex cable.
The thing that I'm getting hung up on, each counter on the module has 10 pins assigned to it. I keep going through the manual, but I'm having trouble understanding it. Went to NI and the engineer there basically just copied and pasted the same part of the manual that I didn't understand. When asking for more details, about the gate +/- for example the response I got was that "you can if you want to gate the signal you use the gate pins"...I assume that means you can use those pins as a switch to take the signal or not, like you would the Gate on a FET used like a switch. Just an example of how detailed the responses are :-)
Anyhow, I'm reading through and it sounds like each of the inputs almost has multiple functions that overlap, but I'm having trouble digesting it. Can anyone help out with the wiring on this?
Just FYI - Short term, I have 1 sensor that will count RPM as 1 pulse per revolution. We will also want to do direction which will require a second sensor with the two set up much like the quadrature function requires. Only still both will have only 1 pulse per revolution, rather than an encoder with say 120 pulses per rev. Will eventually need to wire up both, but I think if I can figure out just the one I can use that to figure out the rest of the setup on my own :-)
Thanks a bunch!
LV7.1, LV8.5
Solved!
Go to Solution.

External Connections:
Sensor common connected to source - of counter
Signal from sensor connected to source + of counter
Any gate signal you would use for this application would be generated internally using another counter and then internally routed to the gate of the counter that is counting the external pulses. In this case the gate signal would provide an accurate window of time in which to count pulses. An example would be measuring RPM. If you decide to measure pulses for an entire minute, how do you accurately define a minute? If you don't count for exactly a minute, your RPM measurement will be incorrect. Software timing won't work.

Level detection PXI 6624

Hi all,
I am trying to find out some details about the level detection in PXI 6624.I have a very simple timing measurement to perform. Start trigger at P1@9V and stop the trigger when P2 @-9V and measure the time elapsed( expected time is 1-1.4sec)
How to configure the CounternGate Signal in level detection mode? The UserManual says it is possible. I need help figuring this out.I see there is optical isolation for the inputs and I would think the inputs are only Supply/Gnd referenced.
Appreciate any help.
Neha

Hi Neha-
       I was looking a little further into your question and I made some assumptions in my previous post that I should clarify/possibly retract. The 6624 is a counter/timer card.  In the user manual it clarifies that digital low is anything below 0.8V and high is guaranteed anything above 4V. So, in reading your first post over, I assume that you are reading two square waves that jump from 0-9V, correct? One on P1 and the other on P2, with one line inverted? Then it sounds like you want to measure the time between the 9V on P1 and the -9V on P2, correct?
     If my understanding is now correct, then you should not use the level trigger detection example in LabVIEW, since it is for one signal on an analog line. Instead, what you should use is two-signal edge-separation, which measures the time between two different edges of two different signals.  Using the timebase, this measurement begins counting on the first active edge on the AUX line and latches the count into memory on the first active edge of the gate. What occurs internally is that a pulse is created with the first active edge of the AUX line and ends on the first active edge of the gate. The counter then performs pulse width measurement on this created pulse.
     Here is a link to a page on our website that will help you with this task:
KnowledgeBase 2D9G49EV: How Can I Measure the Time Between the Rising Edges of Two Digital Signals?
     If, however, you are measuring two analog signals, you will need to get a DAQ card with analog inputs.  If this is the case, I will refer you to our technical sales department at  (800)-433-3488.
     I apologize for any confusion, and hope this clarifies what you need!
Gary P.
Applications Engineer
National Instruments
Visit ni.com/gettingstarted for step-by-step help in setting up your system.

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

Pulse width measurement with FieldPoint CTR-502

I would like to measure the pulse width of a signal (ranging from 10 ms to
400 ms out of a signal with period width of about 1 second). I would like to
use a fieldpoint counter module FP-CTR-502. I could find examples on how to
measure frequency but I did not know how to alter it in order to obtain the
pulse width.
Thanks,
Martien

To measure pulse width of a fixed-period signal, you only need to use one counter, so the configuration and program would be different than the frequency measurement example. Set the count source for counter 0 to "32kHz Reference" and the gate source (and wire your signal) to "Gate Input 0." You'll also need to create a control channel to reset counter 0 (as described in the frequency example).
Your LabVIEW program should run as follows:
- When Gate Input 0 becomes true, do nothing
- When Gate Input 0 becomes false again, read then reset counter 0
- repeat
You can use FP Advise to wait for the gate to change (just like the frequency example).
Once you have the number of counts, you can divide that by the frequency (32 kHz) to calculate the "on tim
e" (pulse width) of your signal.
Regards,
Michael Shasteen
Applications Engineering
National Instruments
www.ni.com/ask
1-866-ASK-MY-NI

Low frequency measurement (1 to 5 Hz) issues - Reg

Hello All,
i am facing a problem in measuring Low-Frequencies in the range of 1-5 Hz. I am using VIs used for pulse-width measurement and the card is PCI-6031E. i am generating frequency using PCI-6013 card.
Actually i am trying to develop an application for measuring the speed (RPM) of the motor which runs very slowly. so if i miss one pulse per second also, when i multiply that with 60 it will be big error.
So if any can give me a solution that will be big help to my issues.
Thanks.

Hello sathiskumar,
I'm not sure what you mean by missing a pulse but I think what is
happening is that your counter is rolling over and starting to count
from zero again. Every time the counter rolls over, it will
output a pulse. You can connect this signal to another counter
and count how many times your first counter has rolled over. That
way, if you don't receive a pulse on your first counter before your
counter rolls over, the second counter will have a record of how many
times this has happened.
I hope this helps!
Eric
DE For Life!

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

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.
I am not allergic to Kudos, in fact I love Kudos.
Make your LabVIEW experience more CONVENIENT.

Triggered single pulse width measurement

I am trying to measure the width of a single pulse, but would like to use the pulse itself as the trigger for a counter input pulse width read using a PXI-6608. I would like to do this since the pulse can come at any time (much longer than any practical timeout) and I would like to avoid having to place a DAQmx read in a while loop waiting for the pulse to appear. Also, while the pulse is high, I would like to produce front panel feedback (light a boolean indicator). I seem to be able to achieve that by using a digital input line, but again requires a DAQmx read in a while loop. I haven't had much experience with triggers and my attempts so far appear to seem like triggers are not compatible with counter input pulse width measurement. Is it possible to set up a trigger for a pulse width measurement?

Hello kayotik,
I think the best thing to do here is to use separate while loops. You can put most of your code in a main while loop, and then put your DAQmx read in a separate while loop. Both loops can run in parallel (just don't wire any outputs of one while loop to the other while loop, because then one will become dependant on the other). In order to pass data between the two loops, you will need to use a local variable. The DAQmx read can write to a local variable, and the main loop can read from that local variable.
You will also need to stop both loops with a single stop button. This article shows how (and also demonstrates the use of local variables to pass data between independent while loops):
http://digital.ni.com/public.nsf/allkb/267704CDE91156D186256F6D00711AAE
Colden

PXI-6624 Pulse Frequency measurement

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