Write a VI in Labview to detect the time

To write a VI in Labview to detect time T when the voltage across the capacitor rises to 0.6321 of the applied value.
Then knowing the value of R, C can be calcul\ted by: C= T/R . Please where will I start.
C = Capacitor
R = Resistor
T = Time
The equation t=RC can be rearranged to show that Vc = 0.6321.E (V)
Where do I begin. I have looked the Labview tutorials.

How are you reading the voltage ? I guess you must be using an DAQ card to do this right ?
If you have a card which can read the voltage in a specific interval of time (that you can specify) for a certain number of readings upon triggering (say every 10 microsec 1 reading for 10msec = 1000 ADC reading). The device must be having a buffer to keep all these data as well (so that you won't interrupt the device until it finishes). Once reading finished, you can read the buffer and look for the time reading 0.6 x applied voltage (or close). Once you see this reading, you can calculate the time as [the index of the reading x 10micro sec].
The key here is to find the card that can do it this way.

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I want to write a program in LabView then pass the test results to teststand to check if it pass or fail without displaying the test stand program,

I want to write a program in LabView and create an execute but I want to be able to pass test results to test stand to find it the unit pass ar fail the test then save the data to a database. How would i go about it.

What's confusing is your statement that you want to do this "without display the test stand program". You can minimize the TestStand UI to the task bar but if you don't want TestStand to be running, how can TestStand evaluate the result. Explain a little more please.
In the message body of your post, you just say you want to create a LabVIEW exe and pass the results to TestStand. What I would recomend is that instead of an exe, you create a dll and use TestStand's DLL adapter to call it and return the results. TestStand will evaluate it and do the logging.

I have to write in my name and Serial, all the time!!!?

I have just bought the latest version of Final Cut!
After installing the program I always have to write in my name and serial!? Everytime I starting ech different program in the Final Cut Studio? The programs are working after I do that, but it`s very anyoing to have to do that every time!
What is the problem!?
//Mathias "CB"

You find info how to fix it here:
http://discussions.apple.com/thread.jspa?threadID=965240&start=0&tstart=0

HOW CAN I GET THE TIME IN EXCEL SHEET USING WRITE TO MEASUREMENT INSTRUCTION

HI, I am using GET TIME IN SECONDS ,and after that i placed SECONDS TO DATE /TIME instruction ,and i had taken a write to measurement file instruction
to get the time in excel sheet. Now i am not able to connect write to measurement source to seconds to date and time output . Is there any solution.
I am attaching my VI file also.
Attachments:
TEST.vi ‏43 KB

Hi
Im using Labview 8.2. Currently it just shows the data without the time. Im not sure what to do. It works perfectly though. I just want the time to appear on my notepad along with my data
holla
Attachments:
Testing1.txt ‏1 KB
Untitled 231_LV80.vi ‏23 KB

Connecting the time capsule to a wireless network (university)

I just purchased my first mac computer, and the time capsule. I am a university student, and my housing has wireless network, so i would need to configure it to that network (which requires registration). When I first opened everything up, I could see the time capsule in the airport utility, but now I cannot. I dont really know where to go from here, because all of the manuals go from being able to detect the time capsule. On top of that how do I connect the wireless to the registration required network? Any help is much appreciated.

how can I use the time capsule as a "wifi acceptor" to connect with my wireless network, and then boardcasting wifi signal to my devices?
Unfortunately, this is not possible.
In order to broadcast a wireless network with Internet access, the Time Capsule must be provided with a wired Ethernet connection at its WAN "O" port.
Check wtih your Internet Service Provider to see if they have an adapter or other device that will provide a wired Ethernet connection to the Time Capsule.

Formatting the time stamp in "Write LabVIEW Measurement File"

When I use the "Write LabVIEW Measurement File" vi to write data
the files first column contains the number of seconds since the staart of the file
How can I get the computer date and time or at least the time HH:MMS???
Tom
PS, And how can I put some sensible label on each columns in the file?

Tom,
The vi I'm attaching demonstrates how to use the computer system time for the timestamp on your LVM file. It takes a reading from the DAQ Assistant and applies a system time stamp. It's in version 7.1, but let me know if you need it in version 7.0.
As for inserting meaningful column headers, you won't be able to do that with the express vi, but you could use the regular file i/o vis to create a file like that is similar to a LVM file, but is a little more customizeable and can be formatted however you like. The express vi is meant to be a quick solution, but does not offer all the versatility of the vis on the palette. I hope this helps you out. Have a good one, Tom!
Tyler S
Attachments:
LVM_timestamp_7_1[1].vi ‏265 KB

How to detect the diskette is write protect?

I would like to write a file to a diskette. Before that I would like detect the diskette is write protect or not? and prompt a meaningful message. Could anyone help? Thanks!

Check the file API...there is a "canWrite()" method...I would assume this returns FALSE on a write protected disk. IF that does not work, then trying to write an actual file to a write protected disk would throw some kind of exception...which of course you can trap.

How to set the time interval for data obtain through labview via write measureme

I'm need to programme to obtain data from oscilloscope. Currently my laptop able to communicate with Agilent DSO6014A oscilloscope via USB. I'm include the write measurement in mty program and save the data in .lvm file. But the time interval in the data are too small which is in micron seconds. Is there a way to modify the interval values?

The attached file is the capture of my diagram. Thanks.
Attachments:
Capture.PNG ‏56 KB

LabVIEW/SignalExpress: How can I automate measuring the time between two pulses?

Hi everyone, bit of a newbie here so please bear with me.
I'm a student at a university conducting a muon decay experiment with an oscilloscope connected to some photomultipliers. To summarize, if a muon enters the detector it will create a very small width pulse (a few ns). Within a period of 10µs it may decay, creating a second pulse. The oscilloscope triggers on the main pulse 5-15 times per second, and a decay event happens roughly 1-2 times per minute. I am trying to collect 10 hours of data (roughly 1500-2000 decay events) and measure the time it takes for each decay.
I've been able to set recording conditions in SignalExpress that starts recording on the first pulse and stops recording on the last. The Tektronix TDS 1012 oscilloscope however feeds 2500 points of data from this snapshot into a text file (for use in excel or other software). Even if I perfectly collected the data, I would have 100,000+ data points and it would be too much to handle. I don't know how (or if it's possible) to reduce the sample size.
To conclude, using Labview or SignalExpress, I would like to be able to have the software
1. Differentiate between the single pulse detections and double pulse decay events
2. Record only when two pulses appear on the oscilloscope
3. Measure the time between these two pulses and ONLY that to minimize the amount of data recorded.
Any help would be GREATLY appreciated, thanks!

Hi wdavis8,
I am not that familiar with Tektronix, but there should be a place in the dialog that you go through when you create the action step to acquire date to specify a sampling rate. That would allow you to reduce the number of data points you are seeing, but may reduce the quality of the data.
If it’s just a matter of that much data being hard to dig through when you have that many points, you could do some analysis on the data after the fact, and then create a new file with only the data you want to look at. For example, you could identify the peaks in the data, and based on the distance between them or the difference in magnitude, selectively write data to a new file.
Here is some information about peak detection in LabVIEW:
http://www.ni.com/white-paper/3770/en/
You could also do some downsampling on the data to get fewer data points:
https://decibel.ni.com/content/docs/DOC-23952
https://decibel.ni.com/content/docs/DOC-28976
Those are just a few quick ideas.
Kelsey J
Applications Engineer

Can I call .m files from a LabVIEW executable without the full development version of matlab installed?

I have an executable that I am trying to build (and distribute). Right now, it has Matlab script nodes that call some matlab .m scripts that someone else wrote. The target PC will not have the full development version of Matlab installed. Would that work? I have tried to compile the .m scripts into a DLL, but I can't import that to LabVIEW because of the special Matlab types (*mxArrays). I have also tried to write a wrapper around that DLL, but with no success. So now I'm wondering if I can either call the Matlab .m scripts directly from a Matlab Script node OR if I can call my Matlab DLL from within a script node. OR any other idea someone might have...
Thanks a lot!
-Matt Bradley
************ kudos always appreciated, but only when deserved **************************

Simon,
I looked at MathScript and am considering using it, but one thing that is not clear to me is if I will be able to use my .m files like I can with Matlab. I call the same Matlab script repeatedly and it keeps track of some information in global variables (for example, the number of consecutive detections). Can I do that entirely within mathscript or would I have to reload all of the info each time -- if I had to do that, it would mean substantial changes to the .m files ... and that's not an option.
-Matt
-Matt Bradley
************ kudos always appreciated, but only when deserved **************************

Detecting the peak-to-peak value

Hi all,
I just start learning LabView for less than 3 months. With a help from a friend, I did some experiments to measure displacement of a polymer when voltage is applied. The output is given in the form of sine signal (peak-to-peak). When I got this output file (in .lvm format), I will use Microsoft Excel to generate the graph and manually I will calculate the peak to peak value, average them and get the displacement.
My question is, can I do the calculation in Labview? Can Labview detect the value of every peak (positive and negative peak)? I have dozens of data and it time consuming to finish calculating all of them manually. I attached here an example of my excel file so that you can see clearly what I'm saying. I can't attached the .lvm file because it is not a valid extension for attachment in this discussion board.
Many thanks for your help.
Thank you.
Amila
Attachments:
labview calculation.xls ‏377 KB

You can do almost any calculation in LabVIEW. It has a huge set of analysis functions and you can always write anything it does not have. If you can not find what you need in LabVIEW, check these forums and the LAVA forums; chances are good someone has done it already.
What version of LabVIEW are you using? There is a VI, Amplitude and Levels, which does exactly what you want. However, it only exists in the Full and Pro versions. It was introduced about 7.0 or 7.1, so if your version is 7.1 or newer, you should be good. Make sure you understand how it works so you can set the inputs correctly for your application.
If you do not have the Full/Pro version, you can write this yourself more easily in LabVIEW than can be done in Excel (assuming you were equally skilled in both). There are a variety of algorithms, from a simple max/min (use Array Max & Min) to Fourier analysis, peak/valley find, and non-linear fitting. LabVIEW can do it all. So can Excel, but Excel gets unwieldy when your data sets get larger than about 2000 points.
This account is no longer active. Contact ShadesOfGray for current posts and information.

Trying to use labview to analyse analog data from a jump on a force plate and measure peak force (at two points, initial land and 2nd land from jump). Also need to mark the time of flight (time off plate).

Attached is a file of 3 trials of a drop vertical jump activity onto a force plate. the subject stands on a platform off the force plate, jumps onto the force place and immediately jumps up as if going for a rebound. I am able to run this data and obtain a waveform graph with no problems. however, I need to be able to find the initial contact with the force palte, the peak of the drop, the intial time off the force plate (prior to the jump), the return from the jump and finally the second peak (landing from the jump).
I want to calculate the time of flight ( time off the plate and in the air after the intial drop) to calculate juimp height.
I had someone write me a mathscript for it and it works well, however, I need to do it without mathscript as I do not understand mathscript (nor Labview!!).
Please help
Attachments:
Jose_Index and shift register6.vi ‏130 KB
NI post.docx ‏365 KB

OK, but I'm not understanding what you're asking us to do... Are you asking us to explain what the MathScript code is doing? (It's searching the array for the elements when the values are above or below a threshold.) Are you asking someone to convert the whole MathScript code to LabVIEW (we are not a code-writing service), or you just want to be able to calculate the new stuff you want with LabVIEW?
In the future, please do not post proprietary file formats. Most people do not have Word, or Word 2007 for that matter. Please post text files or PDFs. Thanks.

Check control signal and write in 1s, ignore control signal for the following 2s.

I am new to Labview, recently I use DAQ to receive 2 channels, one is expected signal and another one is control signal. If the control signal is higher than threshold (rising edge), write expected data in 1s. Then, ignore the control signal in 2 second. The process is repeated. The attachment is my program but it doesn't work. I use flat sequence to do 2 consecutive tasks but cannot ignore the control signal.
Any help is appreciate.
Attachments:
Save data with control signal.vi ‏187 KB

siva0182 wrote:
Find attached the picture of the vi where I tried to put in timers.one in each of the frame and at the end added one more frame just to measure the time elapsed .
The last frame and the frame with sourcemeter measurment show adifference of about 140 msec.
Is there any way to improve the speed of this portion?
Probably not. It sounds like the Keithly VI is taking 140 msec. You can try opening that up to see if there is anything in there that could be causing an unnecessary slowdown. But trying to tighten it up too much may cause occasional errors (such as timeouts) in trying to get a response back.
But surprisingly I tried displaying the actual timer value at the start and at the start of sourcemeter read function ..but the display of both indicators is almost equal with little difference of only 10 msec.????? I'm not sure which of the several timers you are referring to here. What is the value going into the wait function between the VISA write and the Keithly VI?
When you do benchmarking, the timer functions should be in a frame all by themselves. Having it mixed with another function or VI causes a bit of uncertainty as to when the time was taken. For instance, you dont' really know if the Keithly VI was started before the time was taken or after. (The time was probably taken first, but without a data flow or sequence structure dependency, you can't be sure.)

How do I write an excel file and check what the next empty column would be to put the data in?

I have somehow managed to write the portion of labview that prompts the user for a name. It checks a file to see if they are a new user or not and then assigns a number if they are. The program then acquires data that is to be put into a spreadsheet. Each subject will have ten trials which will have three columns. How do I get the information into the columns and then check each time to see which column it should go into (i.e. the next empty column for that subject). I have attached what I have thus far. I wrote this a long time ago and haven't touched it for some time so everything is a blur.
Attachments:
promptForSwimmerName.vi ‏76 KB
Swimmers.dat ‏1 KB
Main__dummy.vi ‏28 KB

To perform those operations in excel you will use ActiveX. I will attach some examples of using Excel in LabVIEW and you can use these to do exactly what you want.
These three examples show how to manipulate properties, write to excel and read from excel. Let me know if there is more I can do.
Allan S.
Applications Engineering
National Instruments
Attachments:
BorderExample.vi ‏102 KB
ActiveX_write_Rows_To_Excel2000.vi ‏90 KB
ReadExample.vi ‏80 KB

How can I use LabVIEW to send the equivalent of a CTRL D (in VT 100 format) out the serial port of my computer?

I am trying to write a vi that interfaces with a piece of OEM equipment that is set up to talk with a VT 100 terminal. I can't seem to locate the ASCII equivalent string (if there is such a thing) of a CTRL D. Is there a vi that emulates VT 100 commands?

If I recall, CTRL-D is EOF on most ASCII tables.
You'd probably have to use an escape sequence
or if you can use an unsigned 8-bit that might be
easier.
In article <[email protected]>, TLS
wrote:
> How can I use LabVIEW to send the equivalent of a CTRL D (in VT 100
> format) out the serial port of my computer?
>
> I am trying to write a vi that interfaces with a piece of OEM
> equipment that is set up to talk with a VT 100 terminal. I can't seem
> to locate the ASCII equivalent string (if there is such a thing) of a
> CTRL D. Is there a vi that emulates VT 100 commands?

Write a VI in Labview to detect the time

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