peteski

OK, I gotta confess, I have NO recent popculture life. I have to fight for every Ultimate Frisbee moment I can get, and the fight is on multiple fronts... sometimes I win, sometimes I lose... Who the %#!! is Bob Saget??? ? -Pete Liiva

Steve, Did you see the response I posted to your Thermistor inquiry? If not, check it out. In fact, if you need a undergrad experiment, perhaps trying to create a calibration curve with known resistances and checking the results could be a good exercise. -Pete Liiva (aka peteski)

Perhaps this is the "real" reason camera phones are not allowed in some "high security" locations! ... say no more! -Pete Liiva

Steve, I've recently been rather busy or else I might have noticed this and replied earlier. I ran into a similar problem using 10K Thermistors with a USB-6008, and found in looking at the "specifications" that the input impedance of the USB-6008 is only about 144K. This is only an order of magnitude away from the impedance of the thermistor, which introduces non-linearities. I tried to model using the 144k "quoted" impedance, but discovered that I did not have enough information on the USB-6008 output circuit to model it adequately, and the NI tech rep I was contacting about this wasn't able to help very much. In the end, I decided to use a bunch of "known" resistors (measured via ohmmeter to verify values) and create my own calibration curve by measuring the voltage reading of the thermistor detection circuit and relating it to the known resistance. Interestingly enough, what I came up with seemed to create an almost linearized voltage to temperature function! It seemed that over the range of values I calibrated for, the non-linearity of the voltage vs resistance relation cancelled out the non-linearity of the Steinhart-Hart thermistor relation, at least within the allowable error for the application (which was something like a couple of degrees C). I can't guarantee this would be the case throughout the entire operating range of the thermistor, though. I would strongly suggest that you do something similar. Resistors are relatively cheap, and you should know what range you expect to be operating in, so with about a half an afternoon of set-up and work you could have your own calibration curve. I'd be a little leery of sending my results for your direct use, because I can't guarantee that the variation between the USB-6008 that I used and the one you are using wouldn't be enough to throw off the calibration significantly. The USB-6008 is a rather "cheap" device, so I'm not as confident that the production of them undergoes the same "scrutiny" as, say, NI's PCI/PXI MIO cards. Hope this helps! -Pete Liiva

If you need to read all 300 kBytes (I assume by 300kB you mean kiloBYTES, not kiloBITS), if you are operating at the maximum speed of a standard PC serial com port (115,200 baud), then a single 300 kByte read will take approximately 20.8 seconds. If you baud rate is slower, say 9600 baud, then this single read could take about 250 seconds. If you need to operate in this mode, you may want to make sure that you have set the read timeout to greater than your maximum expected read time, and then some (just in case...). A much more elegant approach would be to something like Albert Geven mentioned where you look for data at the serial port, read when data is there, and accumulate the data in data structures in the program itself, performing whatever analysis on the data once you have acheived the requirement of getting confirmation from the device that you have the complete data you need from it. If you make sure that you don't try to read any more data from the serial port then there is available at the serial port, then you can avoid having to handle a trivial timeout error, and keep the timeout value to something reasonable to handle the possible but rare case of the device you are reading from quitting/dying in the middle of a serial read. Hope this helps, -Pete Liiva

Crelf, Not quite the same order of magnitude on the "richter scale" so to speak, but certainly not nearly as sinister either. -Pete Liiva

Well... I'm sure the concept of "imaginary beer" will conjure up various images in the minds of many on this forum! And among those, I'm sure many will enjoy a fine, complex brews at least from time to time! One of my favourite "complex" beers used to be something called "Alimony Ale". It claimed itself as "The Worlds Most Bitterest Brew". I say used to be because I haven't seen it in years. Used to get it in CT when I lived there, but haven't ever seen it here in MD. Any well hopped beer (IPA's especially) are tops in my set of preferences! BTW, I luckily have no experience with the concept of "Alimony" first hand, and hope I never have to! Among imaginary beers, near bears probably shouldn't be considered imaginary, since they are more of a "null" set in my opinion. Crelf might say that Fosters served in Australia fits the imaginary moniker. Personally, I would nominate something like "Pabst Blue Ribbon" or "Milwaukee's Best" for that catagory. Cheers! :beer: :beer: :beer: -Pete Liiva

Laniru, Proper etiquette here is for the requestor to post an example of the code they tried and failed with. Without that reference point, it is rather daunting for even the best Labview Coders on this Forum to know what your issue might be. -Pete Liiva

Congratulations! Best wishes to you and your family! -Pete Liiva

cubnstyl, An interesting aspect to ethernet transfer is something called the nagle algorithm and it might be finding its way into this problem. I encountered this a few years back while programming to control a LeCroy LSA1000 High Speed Digitizer, which was basically an oscilloscope with no screen or buttons, just BNC inputs/outputs and an ethernet interface. The short of it was that I found that if I added ~1450 bytes of blank space characters to whatever communications I sent to the LeCroy, I would increase the speed by at least an order of magnitude or so. It was a clear step function, where one to few characters wasn't enough, and any more then the needed amout did not provide anymore speed advantage, which makes sense considering how the nagle algorithm is designed to work. There might have been a more "graceful" way of getting the same performance, but it wasn't obvious to me at the time and adding the extra characters allowed me to get what I wanted, performance-wise, so I stuck with the kludge. There is no guarentee that this is the problem in your case, nor that somewhere arround 1450 charaters is going to work in your instance, but it might be worth trying by adding different lengths of blank charater blocks to all the commands you send to the scope to see if you get a sudden increase in performance. Hope this helps, -Pete Liiva

Thank you very much, Chris and Jim! I really appreciate the feedback. This will do for now, I'll forward the advice, and reference the forum as well! Just got done with a CDR (Critical Design Review) over here that has had me buried recently. Luckily it went MUCH better then our PDR (Preliminary Design Review). Now comes the hard fun part, putting everything together and making it all work! Take care! -Pete Liiva

Howdy Folks! Somebody at my work place today stopped by and asked me for a recommendation for a guide to starting out with Labview (a "Labview for Dummies", I think he termed it). I drew a complete blank, as I had learned way back during one of the Labview version 2 releases, when NI had what I (dimly) remember to be a very good introductory tutorial to Labview. I noticed that in later releases there did not seem to be as good of an introduction shipping with Labview, but I didn't really concern myself with the fact, since I really didn't need to re-introduce myself. BTW, yes, I did look at the LAVA FAQ, but noticed it happened to be a couple of years old (and the link and name for the second post to the faq end up as dead links when I quickly checked) and I though I'd solicit from the forum some suggestions for books target at beginning with Labview. Maybe if we get enough of a consensus on just such a beginners guide, we could reference this to the homework hunters that seem to ebb and flow with the semester schedule in this forum! -Pete Liiva

Hi Xander, Well, here is a picture of a quick and dirty "simple" approach. I can't guarentee this will work, I happen to be in a busy spell at work and will be out camping with the family this weekend, so I have no chance to verify that this strategy will work. Hopefully you know what "Shift Registers" are. If you don't, look them up in the help function. Getting to understand these early in your LabView experience is important. You will have to find out for yourself what the values are that go into the "address", "write value 1", and "write value 2" for your system. A few things to note. I have this set up to so that the user sets "millisecond multiple" and the program lets the user know what the "Nominal" frequency is. The fastest settable frequency is 500 Hz (the loop sets the port to one state, waits 1 ms, set it to the other state, waits 1 ms, so one cycle is 2 ms -> 500Hz). If you set it to zero, the loop will race as fast as it can, which means there is no direct control over the frequncy, you get what you get and that could change depending on what else the CPU might be trying to do. In fact, this program is unable to guarantee ANY frequency with the stability of even a "bad" crystal oscillator. Hope this helps, -Pete Liiva

Congratulations! Though, it looks like you missed the opportunity to post your 500th post in the thread congratulating you on you 500th post. I'm not sure what I'd call that - recursive, reentrant, not even redundant seem to do it... Regardless... Keep up the great work!!! :thumbup: -Pete Liiva

Quite pro-active! 11:46 AM EDT and its still at 499. Is he holding back? How long can he hold back... -Pete Liiva

MC, Your AT-MIO-16E-10 card is the MIO (Multiple Input/Output) card that is the heart of your data acqusition system. It has analog inputs, analog outputs, digital inputs/outputs, and counter timers. The AMUX 64T card is a multiplexer card that allows the AT-MIO-16E-10 card to read up to 64 separate analog channels, although at a slower maximum sampling rate. It has a temperature sensor on it in case some of those inputs are thermocouples and need temperature compensation. This is a link to the NI manual that covers this card. At this stage, it is somewhat difficult to help without more description of the measurement being made. I might suggest you try using the following example VI assuming you are running Labview 7.1 on the computer you are trying this on. This will allow you to get a better handle on exactly what your voltage vs. time signal looks like, and may allow for some real engineering decisions based on the waveforms. If you get signals from this, you could do "Alt-PrtScn" and paste into Paint or some other program for posting here in the Forum. Without better insight as to the exact parameters of your signal (signal to noise ratios, charateristic time constants, average/min/max event frequency, etc.) it is extremely hard to predict what might do the job for you. -Pete Liiva

Xander, Well, the term "stable" begs for specification! Can you specify how stable you need it to be? I haven't actually done this with a parallel port, so I will make a swag (silly wild a&& guesses) that you ought to be able to sustain a 17Hz +/- 1Hz rate (maybe better, but I can't say how much better) with an occasional outlier here and there. It would be best if the PC you use were as bare-bones in terms of loaded software as possible. It would also be best (for stability) if the PC was not tasked to do anything else while performing this function. If you don't need this machine connected to the internet, then disabling and/or eliminating any form of virus checker/spyware checker would help as well. If you have any budget at all, you could purchase a cheap NI PCI-6601 at this link for about $300 US (maybe another $100 or so for a cable and connector block). You could use one of the counter timers on it to output 17 Hz easily, unless you have some insane stability specification like <<1 x 10-6 frequency drift or something like that. In therory, once you configure the counter timer through the software, it would run independant of the windows operating system until you either told it to stop, shut down the power, or disconnected it. There are probably cheaper solutions out there, but I don't tend to go so far as to try to "roll my own" oscillator circuits or things like that. I know some people who have gotten decent lab equipment off of ebay and at used equipment dealers, so maybe a cheap used function generator might be a possibility? Hope this helps, -Pete Liiva

MC, Most importantly, what do you expect the max count rate should be? Hardware wise, do you mean the AMUX 64T?. If I remember right, the AMUX 64T needs to be connected to a MIO card of some sort to operate. Which MIO card are you using? It ought to have counter/timers, which would be the ideal way to go. If there is alot of noise on the signal, you may need some signal conditioning. Are you in a position to be able to buy or assemble a breakout box to get at the various other outputs from your MIO card, or do you have a connecting block to hook directly to the MIO card? -Pete Liiva

I have to agree. I recently had an issue where someone else had installed NI-DAQmx 8 over a LabView 7.1, and when I attempted to upgrade the 7.1 to 7.1.1, it would NOT take. I tried to "gracefully" roll back the NI-DAQmx, but I could find a good way to do it. I ended up completely deleting and reinstalling LabView and NI-DAQmx 7.5, which was not in the least bit "elegant" -Pete Liiva

MC, What is the hardware you are using for the Analog Input? And also, what is the maximum expected frequency of pulsing? One issue I see here is that assuming that if all goes according to schedule, instead of counting transitions, you are counting the number of samples you "catch" over the 4.03 Voltage level. If you have more than one sample above 4.03 Volts before the voltage drops, each of those will samples will cause a new "count" to accumulate. You may need to set up some way of telling your program to only count once when going above 4.03 Volts, and not to count again until falling below some value close to your low state (say 0.5 Volts or so). And your sample rate is "nominally" 20 Hz, but it depends on a software loop to remain as such. This can be dangerous depending what else might be going on in the background of a standard PC. Depending on what hardware you are using, there should be more robust sample timing options available. -Pete Liiva

My "degrees of separation" (from reality ) are both Mechanical Engineering, although I actually specialized in the thermal side of that disipline and specifically in combustion. Then I gave up on that and decided to move my "test and measurement" experience to another field. I presently use my experience in the field of Laser Altimetry, specifically testing space qualified instruments as well as a bunch of bench level R&D tests. Labview happens to be my "glue" tool to get all the computers and instruments working together, although typically I see my final product as being the data I provide - not the LabView VI's that I develop. This just happens to be the position I work in right now. Strangely enough, I've been working in parallel with lasers since grad school, but until I got to where I am now, I never really had to concern myself with the details of how they work. I've learned alot over the last 7 years - enough to realize that I really don't know much!! just my :2cents: -Pete Liiva

Gary, Perhaps you could open a topic in this lounge with that as the subject? Might be that some in the forum might "filter out" this thread, one way or another. Seems like a topic very deserving of its own thread. -Pete Liiva

Looks like not only your mutiple "arse"s made it through the filter, but your single "######" did too. For what it is worth... I'm ready for a :beer: -Pete Liiva

Nooooo... please don't... I'm not actually USING a language like that, I'm just invoking its name for the sake of absudity! Really, I am... Not, I mean. -Pete Liiva

Mike, Completely off topic, but congrats on the <customize this text> designation!! :thumbup: Well deserved, I might add. -Pete Liiva