fuzzycontrolfreak

Hello, thanks a lot for the replies, it was really helpful. Now it seems I have many options (cFP, cRIO, FPGA PCI and std. PC), all I have to do is check what suits mostly. Regards

Hello All, I am starting a project where deterministic real-time performance is obligatory. Unsurprisingly, we're on a tight budget too What I wanna know is, should I stick to FPGA's for real-time applications, or is just using the real-time module to design an application that would run on any platform (M series PCI for instance) enough. In the latter case, will running the code directly from PC hinder the real-time performance, or is it accessing a real-time processor on the PCI card. P.S. Generally speaking, what makes a piece of HW real-time compatible or not !! Thank you for your valuable response, Omar

Hello there, I usually have trouble designing stand-alone applications on my laptop's widescreen. After i finish the vi, i usually switch to an 800x600 or 1280x600 so that I can easily scale and position the objects in my front panel. Isn't there any smarter way to do this?!! I also have another issue with letting the users use the OS, I have been frequently asked to let the user type a password in order to be able to exit the application and access the windows explorer, is this achievable via G-code or do I have to implement it using other language?! Thankyou very much,,, Bedair

QUOTE (Tim_S @ May 16 2008, 08:48 PM) Hey Tim, I noticed the dt=zero problem, I thougth that this will be adjuted after I enter the time domain data as a waveform, where time stamps for samples are involved in the data. Surprisingly enough, it still gives me the error, and I don't know how to set the 'dt' value. I also suspect that the 'dt' value has to coincide with my sampling rate, otherwise an inaccurate spectrum will be produced. This brings me to another scary thought, what if my DAQ is not able to sample at the specified sampling rate, due to computational time or whatsoever, will the FFT block assume samples are being fed at the specified 'dt' intervals, rather than actually referring to the actual time stamp of each sample?! P.S I have used the modifications suggested by 'rpursley', and the vi still indicates the dt<=0 problem. Thanks,,, Bedair

Hello there, First of all, sorry for the poor paragraphing of my previous post, the reason is that I pasted my original message from NI developer zone, and it ended up quite messy. I have attached a sample code of my problem, and I have tried it and it does the same problem, please see what I am doing wrong, and please note that I use LabVIEW 8.0. Thankyou for your help,,, Bedair

Hello there,I am trying to acquire a signal for spectral analysis. I have set the analog input VI to 1Chan/NSamp/Dbl format, and fed the data to the express spectral analyzer VI. The VI is set to acquire arrays of 100 samples length, before feeding it to the FFT VI. The problem is, however, that the waveform graph I use to present the spectral distribution shows spectral analysis for a bandwidth of 0.5 Hz only (0 to 0.5 Hz), and I have no clue why this happens. I am sure there is something I do not know about how to set the application to go right. P.S. I have also tried the low level FFT VI, the waveform graph shows a bandwidth corresponding to the number of samples being acquired at each iteration, (100 in my case), which really confuses me. I have looked at the examples, and none of them uses DAQ for FFT, they all use signal generators which work fine with me. I have posted this message on the NI developer discussion forum, but no one replied, so does anyone have an idea of what I am doing wrong, any help shall be greatly appreciated... Thankyou for your patience,,,Bedair

Thankyou very much, I am really very grateful for your prompt responses, they were very helpful.

Hello there, I searched LAVA for a similar situation, but found nothing. I am acquiring a signal at a rate of 100S/s, and would like to fill the samples into a 1D array. I know how to do this using a for loop, with number of iterations being assigned as the size of the array. The problem now, however, is that I want the array to recieve data continuously inside a while loop, until i trigger it to stop. It doesn't bother me if the array has to be of fixed dimension, acting as a FIFO buffer, i.e it looses the earliest elements in case of overflow. Could anyone help me with this one. I use LabView 8.0. Thankyou very much...

QUOTE (i2dx @ Mar 17 2008, 08:38 PM) Thanks i2dx, My knowledge of die Deutsche Sprache ist very little, but I got the idea, I bet it is very useful. But actually I do not have a problem with building the application, I just wanna make sure everything will go alright with the DAQ card. I believe that a UPS will assure reliable operation, I'll give it a try anyway. Thanks for all the replies, they were extremely helpful...

Hi there, I am designing a simple data logger for an industrial application, and it seems that the USB-6008 has all the specs needed for my measurements (accuracy, resolution, no. of channels, and sampling rate). I just fear the fact that this is a low end card, and that it might not suite the harsh industrial environment, especially its image as a school lab card. Are there any durability/stability issues regarding the use of the USB-6008 in an industrial environment, just for data logging, knowing that all the specs are compliant to the application, and that we have no problem with the USB conection. Thankyou so much for your help...

Hello everyone, I am acquiring a digital signal from a rotating shaft encoder. The square wave comes at a rate of 36,000 pps, at almost constant intervals. What sampling rules does this application follow. Shall I go after the Niquist Criterion, or a 36kS/s is enough to catch all the signals. Thankyou very much for your help.

thankyou very much J R, I have found the solution to my problem. It seems that the DAQ device is not compatible with any USB cables but the one delivered with the package. I tried other USB cables and adapters, and nothing worked well except the one included in the package. It seems this problem is very popular among USB-6008 users, I do not have any logical reasoning for what might be the cause of the problem, but the original USB cable worked very well. Thankyou so much for your help though ... Omar

I have designed a code that acquires data and controls a certain apparatus. The code woerked well for a long time, but then i had to reinstall my LabView on a new operating system, and during the operation of the previously well operating codes, the DAQ shuts down showing me an error window that says: Error - 50405 occurred at DAQmx Read (Analog 1D DBL NChan 1 Samp).vi:! Possible Reason(s): No transfer is in progress because the transfer was aborted by the client. The operation could not be completed as specified. I suspect there is a problem with the external electronics i'm using. This is because when i execute the program with the electronics unplugged, the loop executes very well without any problems. But when i plug the electronics, it works for sometime and then shuts down showing the error screen. If anyone could tell me what possible reasons could result in this error, so i can track the problem directly, because it seems very complicated to know exactly where the problem comes from. Attached is the file i'm using, all the other files that previously worked well are giving the same error screen. Thankyou so much for your help. Omar

Hi everyone, I'm working on a project in which i'm trying to control the position of a hydraulic linear actuator. I was told that a velocity signal fedback to the controller helps making a much better response. Not much is stated in the control theory texts i have, and i would like to know more about this, especially that i have a velocity sensor that's built in my system. I have already tried control without the velocity feedback and have achieved satisfactory results, but i would like to exploit the sensor, and investigate the improvements. Attached is the control loop for clarification, i would like to know general techniques for tuning the gain 'k' at the velocity feedback loop. If there is any other more applicable or reliable loop to be used, i'd appreciate the recommendation. Thanks in advance for all the replies...

Hey Jeff, I know it might be too late to share an opinion on this, but after reading thr impressive replies, another idea jumped into my mind, it is as follows, The setpoint fed to the coarse valve shouldn't be the actual, a pseudo set poin might be fed to the coarse controller according to the position of the fine valve. So for example, if the fine valve is at one of its extremes (let's say 90%), a set point higher than the actual one is fed to the coarse valve controller, so on achieving it the fine valve will have to compensate by moving its way back to the desirable 50% position, upon which the set point for the coarse valve coincides with the actual setpoint. This will always try to keep the system at a situation where the fine valve is at the midpoint. I tried to make myself as clear as possible here, i hope you got the idea. And good luck with your project...