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Thread: Advanced transient testing

  1. #11
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    thanks

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    Quote Originally Posted by crmaris View Post
    I suspect that the labjack, due to software limitations, cannot catch the right peak voltage drop. So, I tried to measure it with the Stingray but I run onto some problems. In some rails I see the voltage drop but mainly at 12V I catch only a raise and not a drop

    How do you set up the stingray for your transient measurements? You use AC coupling with positive trigger at some mV, right? Also shouldn't the trigger be negative, since you want to catch the voltage drop?
    Ok so its on Channel A, edge trigger, T is set to 62mV right now (though this has to scale depending on the units ripple/noise value), and use the single screen capture. You can use the positive edge trigger because when the transient load drops off there is a rise in voltage as well and since my load time is 10ms it is within the viewable log for both the drop and rise. I don't have it written down if I ever ran it with the negative trigger but it should work the only difference being where i have the vertical line for the trigger point at the rise, it will move to the fall in your shot. I am not setup to test anything today, putting in a patio, but if that doesn't help I can through a unit in there when we get back from the lake and figure out how to help you out this week. OR you can email me at my [H] email with your other questions and some screen shots of what you are looking at.

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    thanks very much for your help Spectre!!

    Mine problem is that the load time is way more than 10ms (about 100ms) so I need more bandwidth to catch the whole drop and I think that the stringray is not suitable for this job. When I manage to capture some decent screenshots I will email them to you to tell me your opinion if they are correct or not.

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    I run some more tests.

    Below is the 3.3V rail transient with 20% load and 6 Amps transient load. In the same time I give transient load to 12V and 5V also.


    Here is quite obvious from where I measure the voltage drop (which is 800mV!!!). The problem is at 12V below.

    here are the 12V readings. I measured from two different points because I don't know which measurement is correct.





    Well the voltage drop at 12V is 64mV or 134mV?


    Also after 140ms and not immediately comes the high spike which is also huge.


    Shouldn't we also measure the upper spike or we care only for volt drops?

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    Well you can log a 100ms result you just have to keep scrolling back through the log so making a nice image for a review is going to be difficult. As for upper spike or lower really whichever hits or goes out of spec. I normally report the drop because typically it gets closest to the ATX12v specification limit, but when I have a rise that gets closer I go with that value unless it is the smaller in absolute magnitude in which case I mention both.

    As for the 12v, it is 134mV initially which is actually really good.............but that spike later on is pretty nasty. I can test for 100ms or 1s with my transient load tester....but normally don't so I haven't seen anything like that delayed result in your last shot. Usually by 10ms most power supplies are recovering from the initial load. I have a unit set to test this week which I can give a whirl with the longer transient loads.

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    Thanks again for your valuable help Spectre. As I see it, it would be better to show both lowest-highest peaks and to do so I have to make new charts. Thats one full day of coding or I maybe show only screenshots from the stingray with the captured peaks.

    As for the high spike at 12V now I realized what it is. My procedure is the following, I run the PSU at 20-50% load, I apply the transient load for about 100ms and then I stop all the loads (transient and normal). So this upper spike it must be done when all loads were removed from the PSU.

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