Duty cycle analysis of multiple channel

I have multiple accelerometer with a duty cycle output (acceleration proportionnal to duty cycle). How can I wire these sensors to the DAQPad 6052E ?

Hi Math,
You will probably get more responses if you post this question to the Data Acquisition list.
When you do so, please provide more info regarding the nature of the signal,
how often you want to acquire it,
and what you want to do with the data.
If you give us enough info, we can answer anything (provided there is funding in place).
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

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Generate and synchronize 6 digital channels with differents phases/frequencies/duty cycles/...

Hello,
For some kind of tests we need to generate, with a 6534 card, 6 signals.
The 6534 has 32 digital E/S and can go up to 20MB/s !
Each channel must be independant so that it can have it's own frequency and duty cycle. But for exemple the second channel can be delayed in reference at first channel. I put an image so that you can understand better what i try to do (3 signals are shown but six are needed).
I see a lot of things on forum that are close to my probleme, but none seems to be as advanced as mine.
http://sine.ni.com/devzone/cda/epd/p/id/4683 -> 6534 doesn't have timers
http://forums.ni.com/ni/board/message?board.id=40&message.id=5167 -> Just a phase probleme
http://forums.ni.com/ni/board/message?board.id=170&message.id=261289 -> Another board
http://forums.ni.com/ni/board/message?board.id=40&message.id=5090 -> Another probleme
I contacted NI support, they send me an exemple on "patterns" but it generates frequencies that are multiple of one with no phase consideration or duty cycle.
Any idea ?
Thanks in advance for your advice and help.
Eric.
Message Edité par Eric31 le 08-10-2007 06:52 AM
Message Edité par Eric31 le 08-10-2007 06:55 AM
Attachments:
Sans titre.PNG ‏8 KB

At best, that's gonna be a pain in the neck with that board. If you need very precise timing for freqs, duty cycles and offsets, it gets worse. If they need to change on-the-fly, it'll be near-impossible.
1. You can only operate 1 hw-timed digital output task at a time. So all 6 signals must be part of that 1 task.
2. Thus, you need to define an output buffer representing the states of those 6 bits throughout your entire generation.
3. There's a bunch of greatest common factor and least common multiple stuff needed to figure out the right output rate and buffer size, assuming you'll want to regenerate repetitively. You first need the gcf of all the transition times to come up with the right output rate since all the transitions need to occur on some integer multiple of the output period.   You'll then need the lcm of the 6 signals' periods, combined with the output rate, to size up a buffer that can be regenerated.
4. Forming the output data array may be quite complex.   Personally, I always do my stuff with raw arrays and I know that interleaving all those signals can be quite tricky, especially if there may be an occasional simultaneous transition.   However, I suppose there's a chance that some of the digital waveform functions *might* make this step a bit simpler. I just haven't played around with that format much.
Editorial opinion: Buy a 6602. You can trigger 6 counters to start with different initial phasing, and will be able to change freq & duty cycle on-the-fly for each one independently.
Editorial opinion #2: For higher channel count apps, I'd also recommend checking out the DIO-64 board put out by Viewpoint Systems, an NI Alliance partner. It gives you much smarter hardware-timed DIO. With the NI board, there can be huge amounts of redundant info in the DO buffer. If you find that your GCF is 10 microsec, but the time between consecutive transitions is 10 millisec, you'll have to stuff 1000 identical values into your output buffer.   With Viewpoint's board, your data acq buffer *only* contains data at the transition times. Timing is controlled by delivering a separate array defining the timestamps that correspond to those transitions.
-Kevin P.

NI 5105 - Measure PWM Waveform Duty Cycle

Will the Positive Duty Cycle scalar measurement in the NI-SCOPE software calculate duty cycle correctly on a PWM (pulse-width modulated) waveform? I have a 400Hz signal that is pulse-width modulated with a 40Hz signal that I need to measure the duty cycle for. Since this is not a normal, continuous waveform (like a sine wave or square wave) I don't know if the NI-SCOPE software will correctly calculate the Duty Cycle. Has anyone tried this with success? I am looking at using the NI-5105 because it has 8 channels, but am open to using other hardware and just multiplex my signals to the digitizer.

The positive duty cycle scalar measurement should correctly calculate duty cycle on your pulse. By default, the measurement finds the base and top of your waveform using a histogram of the Y values (there will be peaks in the histogram at the base and top values). Duty cycle is calculated from the 50% level crossings between these two values. You must have at least one complete cycle and only the first cycle is measured.
If that doesn't work for you, there are a plethora of parameters you can change (except for which pulse you measure - it is always the first). For example, you can set the upper, lower, and level crossing values to specific % or voltage levels. See the documentation and examples for details.
If you need to measure the duty cycle of multiple pulses in the same pulse train, there is a LabVIEW function (Pulse Measurements.vi) which allows you to do this. It uses the same algorithms as the internal NI-SCOPE routines.
In either case, the measurement is independent of the hardware. Any NI-SCOPE device will work. If you have any other questions, let us know.
This account is no longer active. Contact ShadesOfGray for current posts and information.

Duty cycle value & user prompt

1. Duty cycle
The value input in the front panel works fine up to 34%, but then it fails for any value above 35%.
(for input value 35% and above, instrument shows 0.5% instead..for all values..)
How can I fix this to make it between 0-100%???
2. User Prompt for config file
Currently, config file will be loaded via "Load Config" case, but is it possible to kick this off when the main VI starts?
The idea is to force a user to load config file to synchronize between the instrument display and the LV front panel.
(when every time the program gets kicked off)
Does anyone have an idea how to do this?
Thanks,
Attachments:
Pulse Channel with Load and Save_no event_v09.4.2.llb ‏2689 KB

I am still having a trouble with setting duty cycle value above 35%...
Tried to add timebase mode subVI in the application function VI, but the outcome is still the same.
Plz help on this...
Attachments:
HP8133A Application Function_mod2.vi ‏129 KB
Pulse Channel with Load and Save_no event_v09.4.3.vi ‏580 KB
HP8133A Ex-Div Timebase_mod.vi ‏48 KB

Duty Cycle measurement

Hello all,
I am attempting to Measure and output duty cycle to a device. I don't have the device in my possession so I have my hardware hooked up to each other. I have NI 9472 output card hooked to a NI 9423 input card. I have found these 2 examples of how to adjust duty cycle and how to read duty cycle. They work great, but the reading of the duty cycle is oppesite of the outputing of the duty cycle. For example if I set my output duty cycle to 60% the reading is 40%. If I set my duty cycle to 30% it reads that it is 70%. I looked thru the block diagram to see if the input was looking for the resting signal to be low or hi. Being a new user it might be right in front of me. Can some one take a peak at them and tell me anything? Thank you.
Attachments:
Modify Duty Cycle while running.vi ‏31 KB
Meas%20Duty%20Cycle%20Cont%20LabVIEW%208.2[1].vi ‏31 KB

Hey greentea2,
You can try taking your waveform data and adding a replica of itself to the end of the data using the Append Waveform VI, so that you have multiple cycles of data to send into the Timing and Transition Measurements Express VI or the Transition Measurements VI for calculating the rise time. I've attached a picture that shows a simple example of this using a sine wave.
If your data does not complete a full cycle that comes back to a similar starting low point, then this example may not work for you or give you the right value. If that is the case, then please respond with a picture of what your waveform looks like, so we can determine how to manipulate it.
Hope this helps,
Attachments:
Append Replica Wave Form Data.png ‏28 KB

Duty cycle on SCXI Modules

Hi All!
I was wondering if anyone could tell me if there is an SCXI Module available that allows me to adjust multiple duty cycles. I need to control the duty cycles of multiple signals simulataneously and was hoping to find a module to do this with. It should be a module that fits to an SCXI housing because this is the system that I am currently using for the measurements. A single module containing multiple counters and counter outputs would be ideal.
I am sure I am not the first to need something like this, so could someone please help me out and tell me how I can solve this?
Thanks to everyone for the help!
Regards
Charel Marais

Hi Wolfgang,
Yes I was thinking of PWM for the duty cycle control. I have done this before using counters on the NI cards, but as you mentioned it is only possible to control 2 signals. I now need to do at least four, possibly more. The system I am using now is a 6036 PCMCIA card as acquisition connected to an SCXI 1000 with an 1102, 1126, 1163R and 1124. I have considered using another DAQ card to provide more counters, but this is a very untidy solution when you have two PCMCIA DAQ cards in one notebook each with a cable going into it. The connectors push very hard against eachother and in long term use, this will destroy the connectors on the cables, the cards and the notebook.
I gather that there is no SCXI module available that provides counters as a normal "slide-in" module (like an 1102 for instance)...? Is there then some other effective way to connect two PCMCIA cards to one notebook?
Thanks for the advice on the counter cards.
Regards
Charel

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

1242ag 100% Duty Cycle

Greetings,
I have a strange scenario I have been brought into at work. A loading dock that has 3 Cisco 1242ag units started filling the spectrum with noise keeping their set channel at 100% duty cycle. I'm using Cisco Spectrum Expert to locate the devices. When we unplug the AP the duty cycle on that channel drops to almost nothing. When plugged back in it may start again or not. Its hit or miss. We replaced 2 of the APs with other Cisco 1242ag units and had the same trouble. We do not use a controller with these units. Is there a setting on these units that would cause them to broadcast like this?
Regards,
Angel

There is only one SSID in the warehouse. The problems started about the same time the local IT guys replaced the PoE hubs with D-Link PoE switches. What I'm trying today is putting one of my Cisco PoE switches in their IDF and plugging three APs into it to see if the problem recurs with those APs. Its the only common link to all APs in the warehouse. I don't like this line of troubleshooting, but its the only thing they have in common and it started about the time they moved to this hardware.

Frquency & Duty cycle Value changes- every time

Hello all
im using pcie 6320 to measure the frequency and the duty cycle of a signal.i have attached my vi & the data measured for reference.The values highlighted in red ,is my actual frequency and duty cycle but values changes for every 1 sec.Please correct me if i have any mistake.
Solved!
Go to Solution.
Attachments:
measure frquency-duty.vi ‏54 KB
HZ-DUTY.JPG ‏37 KB

You'll need to enable digital filtering--insert the following property node into your code (call the property node before starting the task):
Try a "Min Pulse Width" of a few us and increase it if you still are picking up incorrect readings.
The errant numbers are coming from false edges being picked up during transitions, enabling digital filtering will cause the DAQ device to ignore any transitions with a pulse width of less than the set value. Your 475 Hz 72% duty cycle signal should have a high time of about 1.52 ms and a low time of about .59 ms):
656 Hz = ~1/(high time)
1718 Hz = ~1/(low time)
MHz values = multiple edges picked up during a single transition.
Best Regards,
John Passiak

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

Data acquisition from multiple channels.

Hello
Right now, I am able to acquire the signal from a single load cell and display it.But I would like to know of how to acquire acquire signals from two load cells simultaneously.I am using Labview 6i and I am using AI S-Scan with AI config to acquire the waveform.It would be of great help if you could suggest a simple method to acquire the signals.
PS: Please find the attached file used for acquisition from a single load cell.
Looking forward for your reply.
Manasa
Attachments:
test 4.vi ‏102 KB

Hi Manasa,
If I understand what you are trying to do, it is relatively
straightforward to configure your application to acquire data on two channels.
I was unable to run your vi as it was missing some of the subVI’s
from your application. However, your
attachment was sufficient to see what you are trying to do.
Here is how to add channels:
1.
In the I/O Channel Constant, you can add
additional channels by using a comma or a semi-colon. For example, to scan the first four channels
you would put 0:3 in the constant (see attached screenshot ChannelConfig.jpg). To scan the first and third channel you would
put 0,2.
2.
The AI Single Scan VI will now read from
multiple channels. Often it easiest to
configure the output of this VI for viewing by first putting the data into an
array using the Build Array VI. It can
then be plotted in a waveform graph. (see attached screenshot ReadtoGraph.jpg
and WaveFormGraph.jpg)
Just a few notes about “simultaneous” sampling:
Most of the NI data acquisition cards have a multiplexer
between the various input channels and the Analog to Digital (A/D) converter
creating a very small delay between each channel (usually ms range or
smaller). NI does make several data acquisition
cards that can perform true simultaneous sampling, meaning that there is an A/D
converter for each channel.
For the large majority of applications, the small delay
between channels is negligible.
Jared T.
Attachments:
ReadtoGraph.JPG ‏21 KB
ChannelConfig.JPG ‏288 KB
WaveFromChart.JPG ‏61 KB

How do I read multiple channels at one time using labview with the Fluke Hydra Data Bucket 2620a using serial port?

I need to take a reading of 15 channels about once a second. I can read one value at a time using the monitor function on the read values.vi driver, but this takes forever to read all the channels.

I don't have this instrument but I took a look at the instrument driver and it appears that you can only configure one channel at a time to read from. You might want to take a look at the command set for this instrument and see if it allows for configuration of multiple channels. It could be that the instrument driver just doesn't have that built in.
J.R. Allen

How to Read from multiple channels

Dear Sir
I am acquiring data using FP-RTD-122 using OPC Client software. I ahve made one socket for that and i am using command
CWDataSocket1.AccessMode = cwdsReadAutoUpdate
CWDataSocket1.URL = "opc://localhost/National Instruments.OPCFieldPoint/FP Res\FP-RTD-122 @1\Channel 0"
CWDataSocket1.Connect
v = CWDataSocket1.Data.Value
where v is a variant type.But this is 8-channel RTD so how can i read values from all channels using single socket connection Because at presnt i have to use 8 sockets for all eight channels.

At least as of FieldPoint 4.0 and earlier (I do not know about 4.0.1 or later), the OPC Server did not support multiple channel analog items. Thus to read all eight channels of a FP-RTD-122 module, you would need 8 separate socket connections. For discrete modules (boolean), the "All" tag, is treated as a single 8 or 16 bit number.
Regards,
Aaron

How to use multiple channels with one remoteObject .

hi,
I have an application which is accessed through HPPS some
times , also it can be access on server with http service.
so I want to know how to configure config files or add
runtime channels which will support either channel depending on
the server it is accessed over.
Is there any one who can help me to solve this...i need it
soon.
thank you...

Hi,
Please visit the URL below for details on adding channel sets
at runtime. Add multiple channels to the channel set so that the
fall back mechanism works.
http://livedocs.adobe.com/blazeds/1/blazeds_devguide/runtimeconfig_5.html#194376
Hope this helps.

What is the recommended way to do multiple channel, single point sampling for control with an NI PCI-6255 in RLP?

Hello,
I am writing a driver for the M-series NI PCI-6255 for QNX. I have downloaded the MHDDK and have all the examples working. I have also enhanced the examples to do interrupt handling (e.g. on AI_FIFO interrupt or DMA Ring Buffer interrupt). My ultimate goal is to write a driver that I can use for closed-loop control at 500 Hz using all 80 channels of the NI PCI-6255. I may also need to synchronize each scan with a NI PCIe-7841R card for which I've already written a driver. I want an interrupt-driven solution (be it programmed I/O on an interrupt or DMA that generates an interrupt) so that the CPU is available to other threads while the 80 analog inputs are being read (since it takes quite a while). I also want to minimize the number of interrupts. Basically, I will need to collect one sample from all 80 channels every 2 milliseconds.
There are many different options available to do so, but what is the recommended technique for the NI PCI-6255 card? I tried using the AI FIFO interrupt without DMA, but it seems to interrupt as soon as any data is in the AI FIFO (i.e. not empty condition), rather than when all 80 channels are in the FIFO, so more interrupts are generated than necessary. I tried using DMA in Ring Buffer mode to collect a single sample of 80 channels and interrupting on the DMA Ring Buffer interrupt, which appears to work better except that this technique runs into problems if I cannot copy all the data out of the DMA buffer before the next AI scan begins (because the DMA will start overwriting the buffer as it is in ring buffer mode). If the DMA is not in ring buffer mode or I make the ring buffer larger than one 80-channel sample then I don't have a way to generate an interrupt when one sample has been acquired (which I need, because I'm doing control).
I saw something in the documentation about a DMA Continue mode in which it looks like you can switch between two different buffers (by programming the Base Count/Address with a different address than the current address) automatically and thereby double-buffer the DMA but there is no real documentation or examples on this capability. However, I think it would work better than the Ring Buffer because I could interrupt on the DMA CONT flag presumably and be copying data out of one buffer while it is filling the other buffer.
Another option would be DMA chaining, but again, I cannot find any information on these features specific to the NI DAQs.
I tried interrupting on AI STOP figuring that I could get a single interrupt for each scan, but that doesn't appear to work as expected.
I know that DAQmx on Windows has the ability to do such single sample, multiple channel tasks at a fixed rate so the hardware must support it.
Any suggestions would be appreciated.
Thanks.
Daniel Madill

Hello,
The interrupt that will happen nearest the times that you need is the AI_Start_Interrupt in the Interrupt_A group. This interrupt will occur with each sample clock. By the second time this interrupt fires, the AI FIFO should have the samples from the first conversion. If it is easier to use programmed IO, you can read the samples out of the FIFO until you get all 80.
Additionally, you can set the DMA to send samples as soon as the FIFO is no longer empty...instead of waiting for half full or full. This change will reduce latency for your control loop. You can set AI_FIFO_Mode in AI_Mode_3_Register to 0. By the second time this interrupt fires, you should be able to check how much data is in the DMA ring buffer and read the 80 samples when they are available. You can make the ring buffer larger than 80 samples if you see data getting overwritten.
There is no interrupt associated with 80 samples being available in the FIFO or 80 samples being available/transferred by DMA to the host. X Series has much more flexibility with these interrupts.
I hope this helps!
Steven T.

Duty cycle analysis of multiple channel

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