Measuremen​t of the In-rush current

Question

Measurement of the in-rush current slope of a Switch Mode Power Supply when switched on:
Detail:
I am trying to measure the In-rush current slope of a Switch Mode Power Supply' Mains when switched-on. The current is measured on the mains live using a hall effect transformer (TELCON HTP25) and a DAQ (Labview U3-HV). The data are then passed on and processed in Labview.
The computation must be executed at high speed and provide a high level of precision. Although the in-rush current is extremely fast, it is not instantaneous and can still be measured. The attention of this experiment is to monitor the current demand and then decide whether to interrupt the mains or not.
Question:
- What kind of computation should I apply to the data acquired by the DAQ in order to obtain the relevant slope (dy/dx) of the In-rush current and further analyse it? I'm aware that I could simply use the min and max values and compute them but it is not a simple as it seems. If I use this method I will never be certain to obtain the min max at the correct time (or scan # here). The ideal analysis will happen as described in the attached picture. Here you can see where the most relevant info regarding the In-rush current is.
- I also would like to know, How I could obtain an X-axis related to Time rather than the scan number. Could I simply use the (1/scan rate) for the first sample and so on or is there a way of getting it done automatically?
- Additionally, would there be any methods to apply in Labview in order to process data in real time. I.e. As fast as possible? Is the real time module appropriate for this application? Even if the timing Vis, in the real-time module were used, I still don’t seem to be getting the loop speed I require for my application, which I estimated to be in the region of 100 μs.
Thank you very much for your time and help.
Regards,
Badis
Attachments:
in-rush current analysis.jpg ‏181 KB

Answer 1

What do you want to protect: DUT or Fuse?
For analog circuit design: Horowitz:'Art of Electronic' 
It might be a good idea to simulate your protection.  Do you have access to PSPICE? ( PSST: wrong forum here, 'SwitcherCAD' from linear.com is fine for this task, runs from a USB stick, and costs 0$!)
You don't need the short time integrator, if your your break level has a good margin to the line breaker. Line breakers come in different tastes: The rated current and a break characteristik (that is a kind of integration).
Think about using a SSR to turn on and off the DUT. Worst case you have 10ms to break (since SSRs need a zero crossing of the AC current) but you can also turn on the DUT in alsways the same manner..  I assume AC Line testing...
And again If you put 10R in series (Increase R_i of the line source) you slow down and limit your inrush current, but you can correct that numerical...  
Greetings from Germany
Henrik
LV since v3.1
“ground” is a convenient fantasy
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