Multimeter measuring full-wave rectified DC current?

In summary: The question is asking for the average voltage of a full wave rectified DC signal. A full wave rectifier converts an AC signal into a DC signal. The peak of the AC signal is converted to the peak of the DC signal. The average voltage of the DC signal is 7.8 V.
  • #1
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I have this question as a pre-lab for a physics electricity and magnetism lab. (I attached the question as an image.)
I am having difficulty answering the second part:

A full-wave rectified DC current is just the absolute value of the sinusoidal AC current: http://en.wikipedia.org/wiki/Image:Gratz.rectifier.en.png.

I can not answer the this question because I do not know the internal workings of the multimeter.
I can see three possible outcomes:
1) the multimeter is analog, it uses a galvanometer with the needle having some inertia, so the reading would be some sort of average of the maximum amplitude.
2) the multimeter is digital, and thus might measure the rms voltage.
3) the multimeter has no 'inertia', and thus would show the actual time varying voltage V(t).

Any suggestions?
 

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  • #2
The way analog meters work when in AC mode is that they will always read the average value. If you're measuring an AC signal, the meter first rectifies it(either half or full wave), then takes the average value of the rectified signal. It then multiples it by a multiplication (form) factor to display the RMS value.

There is always inertia with these analog meters.
 
  • #3
I have no idea if in the question the multimeter is set to DC or AC.
 
  • #4
What is the question? I don't see a question in the OP! :confused:
 
  • #5
The question is attached in the Picture 001.jpg attachment.

As I understand it now, the question is that you switch a Voltmeter to measure DC voltage. You connect it to a power source that produces a 7.8 V 60 Hz voltage that has been put through a full-wave rectifier.

What will this Voltmeter measure? Will it give the amplitude of 7.8V or will it measure something else?
Basically in the question the guy is trying to measure a voltage tht varies with time V(t) with a DC voltmeter.
 
  • #6
It turn out that the attachment is "pending" for some reason...

Here is the link to the question that I uploaded:
http://e.271828.p.31415.googlepages.com/Picture001.jpg
 
Last edited by a moderator:
  • #7
The peak is 7.8V assuming ideal conditions for the rectifier (no diode drop). A dc voltmeter would meter the average value (as mentioned in my initial post). Can you find the average value of this signal?

Hint: Use calculus to find the average vale of a full wave rectified signal. The wave has a period of pi radians.
 
  • #8
Is this a full wave bridge? Silicon diodes?
 

1. What is a multimeter?

A multimeter is a versatile electronic device used to measure electrical parameters such as voltage, current, and resistance. It typically has a digital or analog display and various probes or leads for connecting to circuits or components.

2. What is full-wave rectified DC current?

Full-wave rectified DC current is a type of electrical current that has been converted from alternating current (AC) to direct current (DC) using a full-wave rectifier. This process removes the negative portion of the AC waveform, resulting in a unidirectional flow of current.

3. How does a multimeter measure full-wave rectified DC current?

A multimeter can measure full-wave rectified DC current by using its DC current measurement function. The meter is connected in series with the circuit or component being measured, and the display will show the current value in amps (A).

4. What is the difference between AC and DC current?

AC (alternating current) is a type of electrical current that periodically changes direction, whereas DC (direct current) flows in only one direction. AC is commonly used for power distribution, while DC is used in electronic devices and batteries.

5. Are there any safety considerations when using a multimeter to measure full-wave rectified DC current?

Yes, it is important to ensure that the multimeter is set to the correct range and function for measuring DC current. Additionally, proper safety precautions should be taken when working with electricity, such as wearing protective gear and following proper procedures for handling and testing circuits.

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