Custom square wave duty cycle in signal express

Hey everyone,
I am using an USB X Series Multifunctional DAQ Model 6361, with labview signal express 11 on windows7 (version 9.3.5) and I am trying to figure out if i can change the duty cycle of a square wave. I need to have one period be at 75% duty cycle and another 25% or something along these lines.
thanks!
Adam

Hi Adam,
I believe another Applications Engineer has corresponded with you concerning this issue already. If you are looking to generate a truly custom square wave where the duty cycle changes from one period to the next then you will need LabVIEW as this functionality is not supported in SignalExpress.
Using the Analog Output along with the Create Analog Signals options will allow you to specify one fixed duty cycle for your square wave, but this will remain constant throughout the generation.
Regards,
James D.
Applications Engineer
National Instruments

Similar Messages

Calculate Square wave Duty Cycle

Hello everyone,
I'm acquiring (with USB-6212) a square wave, "100Hz" with variable duty cycle - which can be 20%, 50% or 80% - for matters of decodification; the acquisition frequency is set to 4k. Actually, I said the frequency is 100Hz, because I get a rising edge every 10ms, but the length of the high level is defined by the communication protocol and that is what I called duty cycle (even though this does not match the exact definition of this property)
Since I need to decode the information contained by the wave, it's necessary for me to be able to tell what the duty cycle is. I've acomplished this so far by taking the derivative of the signal, then calculating peaks and valleys index in the waveform and finally subtracting them, as shown below.
It works ok almost the whole opeartion, however, the acquisition is not 100% exact. Sometimes I get the signal in the picture A, that is ideal for what I intended.
Other times, the signal is like B and the derivative amplitude does not cross my threshold, even though there is a rising edge there. I could lower my threshold to 2, for instance, but then I'd get vulnerable to the signal in picture C, which would accuse 2 peaks, instead of just one.
Anyone have an idea on how to work around this or any other method more reliable than taking the derivative of the signal?
Solved!
Go to Solution.

Well, we can only answer question based on the information supplied! The LabVIEW Mind Reading Toolkit is still in development.
Your application is one where parallel loops may be valuable. In the acquisition loop you read data from the data acquistion device at a rate which optimizes the DAQ perfomance (the >= 2k points you mentioned). The data is transferred to an analysis loop via a queue. In the anaylsis loop you can put the data into a shift register. When more data is available from the Acquisition loop, dequeue it and append it to the data in the shift register. The Duty Cycle section will find two consecutive rising edges and the falling edge between them ( the 10 ms segment). It calculates the duty cycle for that segment. Then it uses the second of the rising edges as the first rising edge for the next segment. Repeat until duty cycles have been determined for all segments.
There are a lot of details which can be imprortant in a process like this. Many of them are dependent on other things you have not specified. What will be done with the duty cycle values? Is the raw data to be displayed? Saved to file? Discarded after the duty cycle is measured? How long will the process continue? How much data can accumulate?
Lynn

Duty cycle two AO signals with a square wave

Hello,
I am running two devices with sending two AO signals (sine wave) out simultanously in my code. I need to duty cycle my signals. in other words, I want to turn ON and OFF the devices continously.In order to do that, I am using a square wave generator with 50% duty cycle. The devices should be running when the square wave has positive values and should be OFF when it is negative.
The code almost does that, but it does not seem to be as fast as it is supposed to, based on the square wave's frequency. I was wondering if anyone can help me with this problem. In addition, I am not sure if this is the best method to do that, please let me know if there is a better way. I also attached the VI .
Thanks,
Pooya
Solved!
Go to Solution.
Attachments:
2AOsignal_dutycycle.vi ‏47 KB

I am using NI-PCI 6071E with BNC 2120as an interface. I am not sure if the problem is the hardware limits. Attahced please find the subvis which I used in my main VI.
one of the which has a for loop (duty_cycle.vi) works just fine and the other one (duty_cycle(new).vi), which is the one I am using in my VI, does not. Any thoughts?
Attachments:
duty_cycle (New).vi ‏23 KB
duty_cycle.vi ‏25 KB

Trying change duty cycle in "Simulate Signal"

Hi,
Anyone knows why I can't change the duty cycle in Simulate Signal? This option appears unavailable for me. How I can access this option? I need generate a wave triangular assymmetric.
Thanks.
Attachments:
simulate signal.JPG ‏66 KB

The dutiy cycle is only for square waves, i.e. a signal that only has two possible states (on or off). The duty cycle defines the percentage of the time the signal is on during each interval.
In any of the other signal shapes, the amplitude is variable and the concept of a "duty cycle" makes no sense..
LabVIEW Champion . Do more with less code and in less time .

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

Generating square wave with variable duty cycle

We like to generate a square wave with variable duty cycle using LabView 6.1 and SCB-68 and this duty cycle comes from some PID controller programmed by LabView by reading a voltage and feeding back this square wave

the story begins with some one called separately excited DC motor
this thing sometimes changes its speed
so we are trying to keep a constant speed
irrespective of the load no matter how it changes
this comes by reading the voltage out from
the tackometer which represents the speed as voltage
then comparing this with a reference set by the labview program
the labview program will send a control signal to some chopper circuit
which is connected to the field of the motor which controls the speed
we are tending to make the labview program as pid controller
that will generate our beatiful square wave with some duty cycle
which will vary to increase or decrease the voltage across the field
we tried "Real-Time PID Control.vi" example and other examples
and we are discussing different solutions for this duty cycle thing
but till now no output
this is our whole story with this DC motor thing

I am working with the NI PCI-5411 AWG in arbitrary mode. How change the duty cycle of the square wave output located at the Sync connector by software?

We use Labview 7.0 and NI fgen 2.1 in order to drive the pci card.Can you send me a VI example?

Hi LtDel,
To achieve this you will need to insert an niFgen property node from the niFgen functions palette into your code flow somewhere in amongst the configuration vi steps. Wire up the reference and error inputs and outputs. Left click on the "property" and select >>output attributes>>sync duty cycle high. Right click and set to "write" then wire in a control or constant defining the % duty cycle for the high phase.
Hope this helps,
Nick

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

"create analog signal" programmatic control of parameter Duty Cycle

I need to generate a square wave with a programmable duty cycle in LabView (not SignalExpress). I can use "Create Analog Signal" for a fixed duty-cycle signal but I cannot figure out how to get at the Duty Cycle parameter to change it programmatically. I was hoping for something like Property Node access but found that this only works for front panel objects.
Is there a way to dynamically change the Duty Cycle parameter in the "Create Analog Signal"?
Solved!
Go to Solution.

The Square Waveform vi found in Signal Processing - Wfm Generation has an input at the top for offset.
- tbob
Inventor of the WORM Global

Help creating custom waveform to load into Signal Express

I've never had to create a custom wave form before so Im completely new to this process.
Basically I need two output channels. Both channels will have the same waveform structure but one will have a time offset. In other words one will be starting while the other is ending.
Channel 1 waveform would look like this: One sinewave cycle (.25hz) then zero output for one cycle. Repeat.
Channel 2 waveform (meanwhile) would look like this: zero output for one cycle (exactly the duration channel 1 is in its sinewave), then one sinewave cycle (.25hz).
Both repeat continuously but out of phase of eachother. This will be a force/deflection test involving two hydraulic actuators applying a load to two points on the same specimen. Basically creating a walking condition where the customer would apply force to one spot then with the other foot transfer body weight to the second spot.
this is more complicated than what the basic function generator can handle but I have heard of people creating their own waveform in Excel and loading that.
Would this be possible for my application? What would the column structure in excel look like?
I've never created or exported a waveform to excel.
Thanks.
SCXI- 1000 Chassis w/ 1346 adapter
PCI 6281 DAQ card
SCXI- 1520 Bridge Board w/ 1314 Terminal Block (x2)
SCXI- 1180 Feedthrough Panel w/ 1302 Block
Signal Express 2014.
Win7 Enterprise

Hello OKors,
What if you were to use a Sequence step to separate the two waveforms (with "Run preceding steps before following steps" AND "Allow hardware reuse" checked) and had them output a finite amount of samples, such that each time one step executed a single cycle? It wouldn't be strictly timed as that would be handled in software rather than hardware, but it is a good place to start.
You could also import a signal that you created in Excel as an ASCII file and choose the delimiter (tab, comma) and start/end rows. It would probably have better timing qualities than using a Sequence step. To figure out what the signal would need to look like, I would recommend saving something to an ASCII file first to figure out what formatting SignalExpress would expect as an input.
Have a great weekend,

Sine, Square & Sawtooth sweep generation with variable duty cycle/rise time & fall time

Dear All !
I request and need some candid advices on the subject issue keeping in view the following notes:
1) I am a novice in LabView.
2) I was an average Electronics Engineering graduate who graduated about 9 years ago and since then I have not been involved in Electronics Engineering.
I have undertaken a task or generation of Sine, Square and Saw Tooth wave forms. All these waveforms are to be frequency swept form 1 Hz to 100 kHz. The amplitude of all these waveforms should be able to be adjusted. The duty cycle of Square Wave should also be adjustable (or better be able to be swept). Likewise the rise time and fall time of sawtooth wave should also be adjustable (or better be able to be swept).
I am considering other options as well but wanna try it on LabView.
I wish to ask that is it possible to execute this task in Labview 7.0? If possible then considering the para 1 & 2 above, is it possible for me to finish this task in 15-20 days if I work on this for about 3 hours a day? If not then what can be reasonable estimate?
I will be extremely grateful if you people can offer advice on whole project or part(s) of it.
Thanking you in advance and requesting urgent response(s).
Solved!
Go to Solution.

Check this thread.
I did some similar coding, it might be usefull to you.
http://forums.ni.com/ni/board/message?board.id=170&thread.id=493477&view=by_date_ascending&page=1
I am using ver 9.0 though.
If you work 3hr /day for 2 weeks you might as well finish book basics 1& 2 and than can do whan you need in a breeze, couple of hours.
Good luck

I need help adding two signal waveforms from a square wave generator using an or gate

Hey Im working on a square wave pulse signal that can be displayed using an FPGA board. I have two different pulses (signal 1 and 2) generated from square wave generators on LabVIEW each with equal duty ratios but different phase offsets. I need to add the two pulse signals together to get another signal (signal 3) showing two pulses (from signal 1 and 2). I have tried using an Or gate but that wouldnt work as expected. Please I need some guidance on how to implement this boolean logic, P.S. Im open to any other solutions. Thanks.
For clarity: Imagine signal 1 = 00001000
signal 2 = 00100000
I need signal 3 to be = 00101000, I hope this emphasizes my point.

The problem is with the third function from the left. Oops, I forgot, I'm not clairvoyant. Maybe if you posted your code, we could really tell you if the problem is the third function from the left ...
Bob Schor

Custom high and low times for square waves

Hi, is there a way to create a square wave that has an incremental HIGH pulse width and a fixed LOW pulse width?
Sorry I'm quite new with labview, any help is appreciated, thanks!
Solved!
Go to Solution.

Hi GBPC,
My name is Jack and I work at National Instruments UK.
I understand you are trying to output a square wave signal with a fixed low time and variable high time in labVIEW.
The reply above works great if you want to use the signal internally. Alternatively if you are trying to output the signal with a piece of internal or external Data Acquisition (DAQ) hardware you will want to use LabVIEWs DAQmx Tool palette.
I have created a quick example below for you to look at that should help you come to a solution. It uses the DAQmx VIs to create and initialize a channel and then runs it in a loop with controls to change the high and low times using a property node.
Hope this helps
Jack. W
Applications Engineer
National Instruments
Attachments:
Variable High Time Pulse Generator.png ‏37 KB

Signal express custom calibration data, where is it?

I have a PXI 1042 rack with 4472 modules. I am using Signal exress 2011.
I have setup with custom scaling for the channels (so that I can log in engineering units rather than volts).
I have just replaced the disk and reinstalled everything. I have got everything working BUT...
When I try to open a previous Setup file it no comes up with an error stating it cant find the calibration values!
Is the custom scaling calibration data stored outside the Signal express setup file, if so where is it?
Thanks
mike

Ok sorted.
Refitted old disc with previous system on it. Ran Measurement and Explorer and then exported the configuration data.
Fitted new disk, imported configuratio data and all the scaling is restored.
Useful lesson, I had always thought the scaling was held in the TDMS files but its in the .nce files from the measurment and Explorer.
mike

Using pulse width modulated signal (square wave) to control when a signal is turned on or off

Using pulse width modulated signal (square wave) to control when a signal is turned on or off
Greetings All
I'm trying to use a labview created pulse width modulated signal (square wave) to control when a signal is turned on or off.
Here's my logic and graphic example:
1) The source wave signal is continuous
2) Use a PWM (square wave) created in labview to control when the signal is turned on or off
3) If PWM signal (amplitude) is greater than 0 play signal if PWM is not greater than 0 don't play signal.
I'm actually using this to step sequence / pulse several separate magnetic coils using my audio card (which has several audio output channels), I have a signal in labview played constantly. Than compare it to the PWM (square wave) which controls if the signal gets played on each separate channel or not. That way I can control which coil is on and off and in what sequence they are activated.
I couldn't find an edge detection for a square wave created in labview so I tried Limits but that doesn't seem to work unless I change the phase manually and that only goes from 1 to -1. I'm just trying to compare the PWM (square wave edges) already created by labview / play a signal if the pulse is greater than 0 and it turns off the signal if it's less than 0.
Should I be doing this another way
Tia
Message Edited by sal22 on 08-16-2009 06:09 PM
Message Edited by sal22 on 08-16-2009 06:10 PM
Solved!
Go to Solution.
Attachments:
PWM control signal block.png ‏23 KB
PWM control signal front.png ‏48 KB
pwm test.vi ‏36 KB

Greetings,
I tried it two ways using amplitude and levels and fft spectrum. The values don't seem to update the way I need them to (basiclly showing a 0 or a 1). I compare the Y values like you recommended but they don't ever seem to update.
tia
Message Edited by sal22 on 08-19-2009 10:05 AM
Attachments:
pwm magnitude not updating.png ‏29 KB
pwm test.vi ‏41 KB

Custom square wave duty cycle in signal express

Similar Messages

Maybe you are looking for