How to get time stamp during a running program

[vhha1972]

Hi All,

As I am new to Labview, I am asking another (possibly!) simple/naive question!

I know how to get latest y-value while running a VI. However, I do not know how to get the associated time stamp (x-value) with the y-value.

I need both the x & y values during the execution of my program to do some other things.

Please see attached code.

I used the Index Array Function. But it only gave me y-value. No time stamp!

Cheers,

Saif

EX_A.vi

[asbo]

1) Double-click the Convert from Dynamic Data node.

2) In the configuration dialog, select Single waveform from the data type listbox.

3) Wire a Get Waveform Components to the output of the Convert node.

You now have access to the Y array, as you did before, but now you can also retrieve the t0 and dt. These can be used to calculate the timestamp of any arbitrary index of the dataset.

[vhha1972]

Hi Asbo,

Thanks so much for your response!

I tried to do what you suggested (attached). Now I have (at least) two problems:

1. My y-value is no more a scalar? Can I use it as is or I need to convert it into scalar. When I connect an indicator to it, I get i, j, k, etc. If i keep this to zero, I should be OK?

2. The 't0' is just PC time. How do I use this to get t = 0, 1, 2, 3 sec etc.?

Any help would be much appreciated.

Thanks a lot!

Saif

EX_A.vi

[asbo]

The Y is an array because it's all of the Y points in a waveform. Use the Index Array node like you did before to get a specific element.

You asked for a timestamp, not an index. If you're looking to get the maximum index, get the size of the Y array and then subtract one (based indices are zero-based). In the last VI, you weren't getting the latest Y value, you were getting the first Y value in the latest block of data.

[vhha1972]

Hi Asbo,

Thanks so much.

I tried your code.

The last y-value is OK (updating). But last x-value is stuck at 999 (not moving).

Please see attached.

Saif

EX_B.vi

[vhha1972]

For example, when I write data to a lvm file from two channels, I get one time column and two y-value columns.

Please see attached image of lvm file.

I want access to the latest elements of this file while I am running my program in Labview.

Cheers,

Saif

[vhha1972]

Hi All,

I will try to explain my problem a bit more...

When I run my VI, my pressure pump starts running, and pressure in the system starts to increase.

I want to calculate pressure (P) over time (t) ratio (P/t) at the instant the rising pressure crosses 80mmHg.

The attached VI does something close. Only thing is that I want the FIRST P/t value when this condition is met and want to use it further. So, I want that first P/t to be stored somewhere temporarily while the program is still running.

Based on the first instant of P/t when the pressure crosses 80mmHg, I want to run a motorized leakage valve for a time period proportional to P/t.

So, I have 2 problems:

(1) How to hold/latch the P/t value associated with the instant when rising pressure crosses 80mmHg.

(2) How to send voltage signal to motorized valve only for a fixed duration (range ~ 1-2 seconds), based on the detected P/t ratio.

Thanks!

VI Attached.

EX_C.vi

[vhha1972]

This is how my pressure versus time graph looks like...

[asbo]

The waveform you get from your DAQ is not continuous, it looks like you're just requesting 1000 samples each iteration. You'll need to use a shift register to maintain a rolling count and add that value in with your latest array size.

[Saverio]

This is also another cross-post from NI: http://forums.ni.com/t5/LabVIEW/How-to-get-time-stamp/td-p/2136340

At some point along the way it seems the question changed. I lost track jumping back and forth.