Maximum/Minimum indicators show incorrect time

[Neil Sampson]

Hi there,

I have a problem concerning the Max/Min indicators in my application. Currently I have data that is acquired from an interface card, connected to Labview 6.1. By plotting the Power vs Time history in a graph, I log the Time and Date at which the Maximum and Minimum Power occurs in indicators. In my program I also have a control that allows me to aquire data at different time intervals, e.g values every 1000ms, 250ms etc.


However, when I set the control to take readings at less than 1 second intervals, the Max/Min indicators do not display the correct times, corresponding to the system clock I have in the program. In some occasions the times are displayed a few minutes ahead of the system clock
for example. The times that appear on the x-axis of the graph are correct thankfully.


Thanks in advance for any help on this matter. Please find included my vi.


Neil.

[Dennis_Knutson]

As was answered here, you need to wire the dt of the waveform. This would be your msec timer interval value in seconds. One word of caution. When you select smaller and smaller intervals, the actual time to do the acquisition and post-processing may be greater than your interval setting. For example, if the acquisition and post takes 300 msec and you have 250 msec selected as the sampling interval, the displayed times are going to be off again. You're going to have to run some experiments tp see how fast you can actually run your loop and then not allow the operator to set a sampling interval less that
that.

[Neil Sampson]

Hi Dennis,

Thanks for the fast reply there. I still have problems with the program though!! I've connected the "Delta t" to my "Select the interval between taking readings (milliseconds)" timer. This has not helped matters. I've experimented with the sampling interval, but still no joy. I wonder if I have connected up the wrong timer, or wired it incorrectly?

I'll attach the modified vi again. I really do appreciate you taking the time out helping me.

Thanks again,

Neil.

[Dennis_Knutson]

Your sampling interval is in milliseconds and the dt value should be seconds. Divide the milliseconds by 1000 before wiring it to the dt input.

[Neil Sampson]

Hi Dennis,

Thanks for the prompt reply....that has solved the problem!

Best Regards

Neil.