Help with rise and fall time

[kwestcobb1]

Hi,

I am new to LabVIEW and am working on a project in which I've run into a small problem.  I'm using a Matlab code to generate a waveform and outputting it as a analog signal and then converting it to a digital one.  I would like to be able to manipulate the rise and fall time of the signal before it is converted and I can't figure out how to do so.  I've been trying to use the Pulse and Transition Measurement example, but it's too far over my head for me to grasp exactly what's going on.  I was hoping someone could give me a few pointers or even tell me what VI I should be using.  Thanks.

[MikeS81]

Hi kwestcobb1,
do you have the analog waveform in LabView? If yes, then you can use the waveform palette to work on your signal. Your values are in the Y array. To change something on your waveform, change the values in your array.

Mike

[kwestcobb1]

The analog signal is being generated within a Mathscript Node in labview which has output Y, which then is running out to a waveform graph.  I'm not sure what you mean by waveform palette and how I would control the rise time from there.  I'm really new at this :(.  Thanks for your advice.

[johnsold]

For us to be more helpful you will need to be more specific. What does you signal look like? What is the sample rate? What is the rise time as generated by your algorithm? What rise time do you want?

Posting the code you have put together already is very useful. Include some typical data and put in comments about what does not work or what you want to change.

Lynn

[kwestcobb1]

The code is for the ARINC 429 databus format (I didn't write it).  The Arinc waveform is RZ bipolar tri-state modulated, meaning it has three states hi, null, low in which

it plateaus for equal lengths. It has a sampling rate of 1.25*10^6, a bit rate of 100*10^3.  I think right now the signal acts like an ideal square wave where there is no rise time.  I don't need it to be anything specific, I just want to be able to change the rise and fall time as labview runs.  According to ARINC 429 waveform characterists an acceptable pulse rise time is 1.5 +- 0.5 usec, so I would like to be able to adjust it in and out of that range to create fault conditions.  I'm hesistant to post the code because it's another workers and I don't know whether I have his permission to do so.  Thank you for your help.

[johnsold]

If I have interpreted your description of the waveform correctly, you do not have many choices.

One bit consists of a high and a null or a low and a null and each bit has a duration of 10 microseconds, that is 5 us high and 5 us null or 5 us low and 5 us null. IS this accurate?

With a sample rate of 1.25 MHz the samples are 800 ns apart. For zero rise and fall times all samples have one of the three nominal values. But the transitions sometimes occur at a sample time and sometimes between samples, so there will be some jitter. The only possible rise time you can simulate is 1.6 us, samples at 0, 0.5 and 1 or 0, -0.5, and -1.

I suggest a faster sample rate which is an integer multiple of the bit rate, perhaps 50 or 100 times the bit rate. Even 2 MHz would give you 0.5 us resolution and three possible values of rise time within the specification.

Lynn