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Posts posted by Gazza

  1. What is the logic behind the cutoff frequencies being defined at the 3dB points?
    why do we use the 3dB points only. is there some thing to do with transient time?
    these are some things we all study in our courses but what's the basis of these concepts. any one who can explain these basic concepts which we use everyday. ???

    This is a method of calculating bandwidth. The bandwidth is the the difference between the upper and lower 3db points.

  2. I just bought a transformer; multi-tapped 0-6-12-24, 12 Amp.

    Does it mean it can go up to the max 24 volts rms - 12 Amp ???

    Yes, that is right. However that is only true if that is how the secondary terminals are marked.

    Some transformers are rated in VA, what does it mean?

    Transformers are always rated in VA. In this case you have a teansformer that is 24V @ 12A.

    VA = E x I

    = 24V x 12A

    = 288 VA

    I hope this helps,

  3. Greetings, all.

    I am looking for recommendations on a decent DMM. Can I get a reasonably accurate one for 100.00 Cdn or less? I just started an electronics course, and want access to a DMM at home.


    Hi Stoodent,

    You can buy a pretty good home meter for that price. Just make sure that when you choose your meter it is a true RMS meter.

    The cheaper meters typically aren't. Also try eBay, I have seen some pretty good deals on there.

    Try the Fluke 110, $117 http://www.action-electronics.com/fluke.htm
  4. Woirking in the Power Electronics and Power Quality field, I deal with UPS's all of the time.

    Even a small 500VA UPS is a very complicated machine.

    It is not designed in two parts, it actually has many more pieces than that. Since most modern UPS's are "online" I will include a block diagram for one.


    This diagram is over simplified. It is missing the boost circuit and all of the PWM control. Not to mention the fact that the rectifier is a 12 pulse SCR bridge.

    Good Luck :)

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