Detect 0% and 100% PWM Duty Cycles on 660X Card

Hi,
We essentially want to be able to detect 0% (all low) and 100% (all high) duty signals as well as > 0% and < 100% duty. However, I noticed that when performing buffered pulse width measurement, if either 0% or 100% duty occurs, the previous detected duty is stored. It seems as if the next edge or level change isn't detected, then the HWSave or SWSave registers store the last successful count. Is there some flag on a status register for the NI PCI-6602 card that would indicate whether PWM is continuing to be detected?
Thanks,
Jeff S.

Hi Jeff-
You might be able to achieve this operation by setting the Counting_Mode to Synchonous_Source mode. Check out the descriptions for bits 2:0 of the Gi_Counting_Mode register, as described in the 660x RLP manual page 3-22. In that mode, you also must set the Gi_Alternate_Sync bit as described on page 3-21.
Without making the change to synchronous counting, you might also be able to glean some useful information about when an error condition has been met by periodically monitoring the Gi_Stale_Data bits, as described on page 3-13.
I haven't tested this, but I wanted to offer a few quick tips to try. Please give these a try and let me know your results.
Thanks-
Tom W
National Instruments

Similar Messages

Using labview cosimulation, how to control PWM duty cycle in multisim

I am new to using Multisim with LabVIEW using cosimulation. I want to ask if there is a PWM component in Multisim that can have its duty cycle be controlled using LabVIEW? I have an algorithm in LabVIEW that outputs duty cycle values from 0 to 1, representing duty cycle percentages.
How do I control the PWM duty cycle in Multisim using LabVIEW cosimulation?
Many thanks,
SPECTRE
Solved!
Go to Solution.

Hi Spectre,
In Multisim, search for the parts base on functionality, there are some PWM models in the database. Have a look at this knowledge base if you don't know how to search for parts:
http://digital.ni.com/public.nsf/allkb/7309A5CABC677296862577ED006EC99E
Aslo, have a look at this knowledgebase:
http://digital.ni.com/public.nsf/allkb/EF391C48CF71AE4F862571B900644F84
This article shows how you can get Mutlisim and LabVIEW to co-simiualte:
http://www.ni.com/white-paper/13663/en
I hope this helps
Tien P.
National Instruments

PWM duty cycle update stalls

Hello
I want to output a variable pulse width modulated signal via counters. The duty cylce should follow a sine or triangle pattern from 10 to 90 percent.
Problem: When I observe the ctr output with an oscilloscope, I see that the update stalls, i.e. for some time, the output is seamlessly variable as expected, but then, update stalls and jumps to a new duty cycle to continue variable again.
I tried several different approaches,
-for-loop with wait ms- timing and single sample,
-timed loops with single sample and
-pulse train ouptut via DaqMX-Write-Counter-n-Samples.
Albeit to no avail. In any case, I get jumps in the PWM duty cycle instead of smooth transitions.
System is either cDAQ 9174 or PXI with 6602. As system load is 99% idle state, I can't imagine the OS at fault.
Solved!
Go to Solution.

Hello, Frank
After looking through some documentation, I think that I need RT-HW for what I want.
6602 cards have STC-2 without buffer, so updating duty cycle is OS-limited. Even in timed loops there is no guarantee that update will run at the specified rate of 1/140 sec. I'll probably just get an error for untimely execution....
With STC-3 based counters (such as cDAQ9074 or X.series PXI 6361) I can load 127 values into buffer which will be processed smoothly but on renewal of samples (every 127/140 sec), I get stalls again, since the OS seems to consider my request inappropriate. I was surprised to find that USB vs PXI does not change the behaviour, though I'd have expected better latency from PXI.
Attached, please find a VI to get an impression of what I tried out. Pardon for code ugliness.
I still hope that I maybe have missed something simple to get running with what HW I got
Best regards
Michael
Attachments:
Unbenannt 1.vi ‏172 KB

Measuring PWM duty cycle with Analog Input

Hello folks,
I have a NI 9205 module and was wondering if there was a way to measure the duty cycle of a PWM signal that I am generating with a separate microcontroller? I have found a lot of examples with Digital inputs but not analog.. Is this possible?
Thank you,
Bob

Hi Robert,
I'm not sure what that error is, try searching for it.
If you want to measure a PWM signal you would usually use a counter input. A counter is a dedicated piece of hardware that is used to measure digital signals. Since the NI 9205 is an analogue device and it doesn't have any counters onboard, you will not be able to select counter input.
I would recommend you get the right tools for the job and buy a digital acquisition device with an onboard counter. It will make reading PWM much easier for you. The NI 6008 has a counter onboard and is only £99. It will also offload processing from software to hardware since you don't have to calculate duty cycle.
If you still want to use analogue post back and we can look into why its not working for you. Tips to start you off: Voltage is the correct setting and Look in the manual and make sure you have connected it like you have configured it (differential, RSE, NRSE page 14)
Lewis Gear CLD
Check out my LabVIEW UAV

How can I measure a 0% or 100% duty cycle signal ?

I want to measure the duty cycle of an input signal using a counter of a 6030-E board.
I work with a PXI Rack under Labwindows/CVI.
My program already works properly for duty cycle between 1% and 99%, but it is not able to detect 0% duty cycle (ie : signal to ground), nor 100% duty cycle (ie : signal to power supply).
The problem is I don't understand how the counter works in such a situation (it cannot detect any edge, as long as the signal is continuous 0V or continuous 12V).
Please have a look on the following code :
1- First, the counter is configured
// Reset Compteur
i_Status = GPCTR_Control(iDevice, iCptID, ND_RESET);
//Definition du type de mesure du compteur (mesure temps impulsion)
i_Status = GPCTR_Set_Application (iDevice, iCptID, ND_SIMPLE_PULSE_WIDTH_MSR);
//Definition de la vitesse d'echantillonage (20 Mhz)
i_Status = GPCTR_Change_Parameter(iDevice, iCptID, ND_SOURCE, ND_INTERNAL_20_MHZ);
//Definition du signal a mesurer (defaut)
i_Status = GPCTR_Change_Parameter (iDevice, iCptID, ND_GATE, ND_DEFAULT_PFI_LINE);
// initialisation du compteur
i_Status = GPCTR_Change_Parameter(iDevice, iCptID, ND_INITIAL_COUNT, 0);
// Preparation du compteur avant de l'armer
i_Status = GPCTR_Control (iDevice, iCptID, ND_PREPARE);
2- Then, every 10 ms, the value of the counter is read, so that I can calculate the duty cycle...
i_Status = GPCTR_Watch(iDevice, iCptID, ND_COUNT, ul_val_cpt);
3- ...and the counter is armed again for the next reading
i_Status = GPCTR_Control(iDevice, iCptID, ND_ARM);
When duty cycle changes from x% to 0% or 100%, the counter always keep the value corresponding to x%.
Even if I reset the counter between each measurement, it keeps this value ! I don't understand how it is possible.
How can I know that the counter didn't see any edge, and so that duty cycle is 0% or 100% ?
Thank you in advance for your help !
FraB

Hi,
Just have a look at this link, it can be interesting for you...
http://forums.ni.com/ni/board/message?board.id=40&message.id=2161&requireLogin=False
Regards
DD

Dynamic Duty Cycle Change for PWM

Hello savvy LabView people out there!
I am trying to do PWM for servo control using LabView.
I have been able to manually move my servo with this: http://www.ni.com/white-paper/2991/en
My goal is to automate the servo position as a sinuisoidal movement, and to do so,
I need to automate the duty cycle to oscillate in 5%~10% automatically over time.
I have looked into some stuff as:
http://forums.ni.com/t5/Counter-Timer/PCI-6602-PWM-GENERATION-Dynamic-sine-duty-cycle/td-p/1522442
But it was not too helpful, as I was also getting Error -200301.
I want to be able to move the servo position at ~10Hz, if that is important, and the square wave freq. for the
servo signal (PWM) has to be 50Hz.
Any help? Thank you!
Attached is what I am trying to do. The sine motion of the servo is (supposed to be) actually paired up with
an analog output from a BNC-2120 board. The servo control part is separated on the top portion.
Solved!
Go to Solution.
Attachments:
ServoTest3.vi ‏110 KB

Is something like this for the PWM look like what you had in mind?
(see attached)
This works, but I need something that responds faster.
For example, the PWM needs to be at 50Hz, which means the loop delay should be able to
go as low as 20ms
In the picture, it is currently 200ms, and this does not run. I found that with 50Hz, the minimum
delay that the Error 200301 doesn't pop up is with 500ms delay, at which point the
accuracy of PWM duty cycle in each period is compromised.
Is there a way to have the loop delay be as low as ~20ms?
Attachments:
Servo.jpg ‏52 KB

How to convert a number to duty cycle (FPGA)

Hi
I want to convert a numerical number to a duty cycle value in FPGA module so I could use it to generate a PWM signal for the numerical value.
I tried dividing it but it shows an error in FPGA as it would produce a float value. I tried even the example of scaled division but the quotient is rounded of to 0 (I wanted to convert an output by multiplying 10/36).
In my project the 100% duty cycle is 360 degrees and 0% is 0 degrees of the motor shaft rotation.
Please help me I need to use it for my project.
Thank you
Dinesh

I am not exactly sure how your duty cycle is setup, but here is a way we have used a number to create a PWM in our FPGA.
If you have 360 deg. then I would guess you want to create a PWM duty cycle that is some fraction of 360, say "number"/360. You could use a for loop where 360 is wired to the "N" and then your "number" can be compared to the current loop count. That comparison would be true/false which could triger a DIO to be high or low. Therefor, if (loop count) < "number" then DIO is HIGH, if (loop count) >= "number then DIO is LOW. This would send out a PWM that has a duty cycle of "number"/360, (multiply by 100 to get in %)
I hope this helps.
--Alex--

Bad Duty Cycle readings

Hello!
I’m building an application in which I want to measure a duty cycle. I can control the “Duty Cycle In” and the FCM analyzes the info and sends a signal to the Motor. I want to measure the “Duty Cycle Out” of the motor. (I attached diagram) For this measurement I just connected a wire to the negative side of the motor. To calculate this Duty Cycle I am measuring the period and the pulse width. The program works very good when I have a “Duty Cycle Out” from 1% to 99%, but whenever is 0 or 100% it shows wrong info. I would expect that the pulse width at 0% or 100% is cero, but LabVIEW shows a value (1,1E-5 s) and calculates a Duty Cycle of about 23% which is totally wrong. Also, if I run the program for the first time and I measure this pulse width with a “Duty Cycle In” of 0%, pulse width is cero., but whenever I change the “Duty Cycle In” to 10% or higher, and then I go back to a “Duty Cycle In” of 0% it shows a value, and calculates a bad Duty Cycle. I don’t know why this only happens when I put higher “Duty Cycles In”, and then I go back to 0%. I measured the signal with an oscilloscope and there is nothing, not even noise! I don’t know how the card gets these lectures. Do you have any suggestions of what can be wrong?
Appreciated!
Solved!
Go to Solution.
Attachments:
Diagram.JPG ‏33 KB

Hi Elmar
Thanks for the reply. I attached my Code. I am measuring the period with ctr0 and pulse width with ctr1. I divide Pulse Width / Period to obtain the Duty Cycle. To detect 0% and 100% I compare the value of pulse width to zero. I created an additional Digital Input, with this channel I check if the signal is high or low. So if Pulse Width is zero, I read from the Digital Input the level of the signal, and then I know whether is 100% or 0%. My problem is when I have a Duty Cycle of 0 or 100%, the DAQ keeps sending a value for the pulse width, and I cannot apply the method explained before. I think this value should be zero, I don’t know if I am mistaken.
Attachments:
PWM_Measurement.vi ‏61 KB
PWM_Measurement.JPG ‏151 KB

Generate complementary digital signals with dead time between each pulse and controlled by duty ratio

I am to generate two complementary digital signals using NI 9606 conected by RIO Mezannine Card to NI 9683 (Half Bridge DO).
I am able to generate the signals but I am not able to put dead time between high and low signal and also, low and high signal.
Requirement:
(1) When the first signal goes high and the second signal goes low, there should be a controllable dead time.
(2) Also when the second signal goes high and the first signal goes low, there should be a controllable dead time.
I am able to do requirement 1, but I am unable to fulfill requirement 2.
Please have a look at my VI and let me know how to go about satisfying requirement 2.
Attachments:
complementary test 2.vi ‏69 KB

Hi Frank ,
I have already taken note of the example Tannerite has provided and have built my vi ( attached in previous post) surrounding that example.
Now I require to control the PWM duty cycle as you can see from the vi using a knob and that control refers to both the signal 1 and 2.
Now the signal 1 end and signal 2 generation requires a controllable dead time. Similarly, signal 2 end and signal 1 geneeration also requires another controllable dead time.
I am able to do either one dead time at a time using delay but not two dead time simultaneously.
I feel that I have two put the delays at the appropriate data flow point. I am working on that.
I would really appreciate if you could give some insight on how to solve this dead time issue and generate two complementary waveform with dead times whose duty cycle can be controlled by a knob controller in fronty panel .
I have also posted the required timing diagram for reference as suggested by Tannerite.
Best regards.

How to decode duty cycle using LabVIEW?

The duty cycles are output of an accelerometer, which are the input of the DAQcard-DIO-24, but how to decode the duty cycles after acquisition? I knew a timer would be useful, but have no idea about how to perform with labview.
Thanks a lot.
--yang
Message Edited by YangLi on 02-23-2006 05:43 AM
Message Edited by YangLi on 02-23-2006 05:48 AM

This will still be a very difficult task without dedicated hardware, and the 1ms resolution will still be relative to other things outside your control. Timed Loops give the tasks they execute a high priority in terms of processor time, but Windows will always be able to preempt LabVIEW in favor of anything it pleases (anti-virus software, automatic updates, screen redraws, etc.). The Timed Loop gives you the ability to dynamically handle what you do in such a situation (discard loop iterations, abort, etc.), but this is not ideal.
You would really be much better off, as Dennis said, with dedicated hardware. Most NI MIO or DIO boards come with a couple counters, which can measure high times and low times against a high-accuracy clock and calculate the duty cycle. The advantage here is that the hardware is doing all the work with real-time accuracy, so you don't have to worry about software-timing and Windows instability. In addition, the API for this in LabVIEW is much simpler.
If you choose to try using timed loops, then you will have pair each digital acquistion with a timestamp and for a sort of digital waveform.
Jarrod S.
National Instruments

Analog signal duty cycle incorrect

I am using an NI PCIe 6535 board to send digital timing signals to a custom PCB.
The signals are digital square wave signals with various duty cycles and phase shifts.
I also need to send a 12 bit ramp signal to the board.
I am having issues with the frequency.
I need the timing signals to run at 833.33333 khz.
I need the lsb of the ramp to run at 416.666666khz.
To create the timing signals I am using "Create Analog signal", so that I can set up the square wave with the appropriate phase shift and duty cycle.
Then I conver from analog to digital.
I am using a DAQmx generate to output the signal to the PCB. I have noticed that the DAQmx gen frequency directly controls the ramps frequency.
However for the digital timing signals there is some scaling factor. The frequency of the digital timing signals can be set in the timing signals them selves. The sample rate in the analog signal also effects the frequency.
To get the frequencies that I need. I had to set the"create analog signal" sample rate at 2.778G S/s, the "create analog signal" frequency to 1.2889GHZ, and the DAQmx generate frequency to 1.66666 MHZ. At those numbers, I get the timing signals to output at 833.333KHZ and the second bit of the ramp at 416.6666HZ (for the ramp I upped it to 13 bit and I don't use bit 0, as it outputs at 833KHZ).
However at these settings all of my timing signals have the same phase, and the same duty cycle, even though I have them set differently.
Can someone please help? I think the issue is that I have the sample rate and frequency of the "create analog signal" block set too high, but if I set them lower my signals will not be at the right frequency.
Attachments:
timing signal 1.JPG ‏44 KB
timing signal 2.JPG ‏47 KB
daqmx gen.JPG ‏55 KB

Hi David,
We found that there seems to be a weird divider between the sampling rate of the analog signal module, the analog signal sample rate, and the f daqmx gen.
After various tests we made a chart of what we observed. Fsignal and sample rate are values set in the "create analog signal" module, Fdaqmxgen is set in the "DAQmx generate" module. We used a "create anaolg signal" module to create the square wave, then convert analog to digital convert the square wave to digital.
We have "repeated signal" and "N periods" checked.
Fsignal
Fdaqmxgen
Sample rate
Frequency measured on the scope
1GHZ
10MHZ
100G s/s
100KHz
100MHZ
10MHZ
100G s/s
10KHZ
1GHZ
1MHZ
100G s/s
10KHZ
10GHZ
10MHZ
100G s/s
1MHZ
100GHZ
10MHZ
100G s/s
10MHZ
100GHZ
10MHZ
100G s/s
5MHZ
The equation we came up with is Feff = (Fsginal/FDaqmxgen)*1000.
To meaure the frequencies were using an HP 54600A oscilloscope, and probing standoff pins on our custom pcb.
We have several versions of the project, attached is the latest one.
Kyle,
How do I set the compression to false?
The picture below looks like labview? We are using signal express.
I can't change the frequency on the DAQ mx gen because I need the ramp to run at a set frequency.
There is a divider between the daqmx gen and the f signal. I have to set the Fsginal in the GHZ to get it to out at the right frequency. The equation we came up with is Feff = (Fsginal/FDaqmxgen)*1000.
Thanks,
Devin

Problem to measure 0% and 100% duty cycle of a PWM.

Hi,
I am using counters of USB-6341 to measure duty cycle of PWM just by following the example 'Meas Duty Cycle-Buffered-Finite.vi'. It works almost all the time. However, when the duty cycle of a input pwm is 0 or 100%, the DAQ can't read anything, in another word, it can't measure 0 or 100% duty cycle.
How to modify that?
Thank you very much :-)
Nan

That's the thing about PWMs, you never really know if the PWM is 0% or 100%.
Let's say we have a 50% duty cycle, at 1/2Hz. So low for 1 second, high for one second right? What if we run at 1/20Hz, so low for 10 seconds high for 10 seconds. Or is this a 0% duty cycle for 10 seconds, and a 100% for 10 seconds?
A true PWM read will never be 0% or 100% it will just keep waiting until the trigger is seen, and recalculate the frequency and duty cycle of it. The solution to your problem is for you to define a duration to watch for a change, and if one isn't seen, then you can define 0% or 100% appropriatly.
So I would recommend taking your duty cycle like you normally are, and then at the same time watch the digital signal for however long you want, if the digital line does not change state, then output 0% if it is low and 100% if it is high and ignore what ever duty cycle you read. But if the digital line does change state, then use the read duty cycle as the actual value.
Unofficial Forum Rules and Guidelines - Hooovahh - LabVIEW Overlord
If 10 out of 10 experts in any field say something is bad, you should probably take their opinion seriously.

I want to store the data form the PWM and the value of the changing duty cycle into a file simultaneously and continually

i want to store the data form the PWM and the value of the changing duty cycle into a file simultaneously and continually but having problem.Please can anyone help out.
Attachments:
data.vi ‏60 KB

Hello,
Have you looked at the "Write Binary File.vi" and "Read Binary File.vi" examples?
They give you a good clue as how to write and read arrays to and from binary files.
For your data it means that you could put the two data items to write in an array and write the array to file, for the read its important to in what sequence the number were written to file.
Kind regards,
André
Regards,
André
Using whatever version of LV the customer requires. (LV5.1-LV2012) (www.carya.nl)

How can I vary a PWM´s duty cycle inside a while loop?

Hi,
I'm using the "Generate Pulse Train.vi" to generate pwm signals in counters 0 and 1 in order to drive a DC motor both ways.
The problem is, I need to control the movement of the dc motor with my PI controller which is inside a while loop. I've tried letting the "generate pulse train.vi" outside the while loop, but the problem is, it only changes the value of the duty cycle when the loop is stopped. I also tried putting it inside the loop, but then it doesn't even work.
So, how can I vary a PWM´s duty cycle inside a while loop?
I'm attaching the VI with the PI controller.
Thanks for your help!
Guilherme
Attachments:
controleValvula.vi ‏332 KB

Here's some code I threw together a while back to change a duty cycle on the fly. It generates a fixed 5KHz or 25KHz frequency depending on laser selection, then allows duty cycle to be changed continously. Maybe you can use the premise of it for your application.
~~~~~~~~~~~~~~~~~~~~~~~~~~
"It’s the questions that drive us.”
~~~~~~~~~~~~~~~~~~~~~~~~~~
Attachments:
Pulse_Width_Modulator.llb ‏197 KB

How to generate a pwm whose duty cycle has to be varied depending on the frequency of the input trigger??

Sir/madam,
I am quite new to the Labview FPGA module.
I am currently working on an application where i have to generate a pwm to control the ON time duration . The pwm ON time depends on the frequency of an input signal.I want to retrieve the ON time value from a lookup table which contain the duty cycle values for the pwm at different frequencies of the input.This input also has to work as a trigger. The input is pulsed and the trigger has to generate the pwm at every rising edge. I am using a PCI 7831R- RIO series. I am urgently in need of some help and i have hardly a couple of weeks before i meet the deadline.
I am trying hard to learn the basics from the shipping examples but not able to quite make my vi work.
Kindly lend a helping hand and i would be very grateful to anybody who can help. Thanks a lot in advance.
Do ask in case of any clarifications required. I think i have explained my problem quite well.

Hello Manu,
You can refer
Developing a PWM Interface using LabVIEW FPGA or PWM Output with LabVIEW FPGA
How this helps.
Best Regards,
Hardik Asawa
AE
National Instruments
Message Edited by Hardik Asawa on 05-05-2010 12:46 AM

Detect 0% and 100% PWM Duty Cycles on 660X Card

Similar Messages

Maybe you are looking for