Question about basic AC measurement using oscilloscope

measure mains ac cro

1.What is the purpose of the **broken link removed** coupling switch in a CRO?
2.What levels of precision and accuracy are obtainable from the CRO when it is used to measure frequency?
3.Compare the precision and accuracy of voltage measurement using CRO and Digital Multimeter (DMM) ? Discuss the cases for both DC and AC voltage measurements?

oscilloscope isolation transformer

you are talking about cro or dso?

oscilloscope measuring ac

1.What is the purpose of the AC-GND-DC coupling switch in a CRO?

In the DC position the signal is input directly to the amplifier of the oscilloscope. In the AC position the signal is coupled to the amplifier by a small capacitor which blocks any DC component of the signal, allowing the AC component only to reach the amplifier. In the GND setting, the input is grounded (usually used when you want to zero the vertical trace).

As to the others, I suggest visiting:

http://en.wikipedia.org/wiki/Oscilloscope
**broken link removed**

ac voltage measurement using oscilloscope

Sahara said:

you are talking about cro or dso?

Click to expand...

Yes, I am talking about CRO.

measure mains with oscilloscope

1. In DC mode the display will show the exact waveform. In AC mode, the dc components will be removed and only ac components will be displayed. This mode is useful when we are monitoring the ripples/spikes of a power supply or when u are checking transient response (in case of a DSO). GND mode will not display anything other than the horizontal ground trace. At this time you can position the trace anywhere in the display using vertical position knob as per your requirement

2. Basically in CRO, the frequency is measured based on zero crossing principle. In DSO, by finding the highest component in their frequency spectrum. Both methods will not display the frequency value correctly when the signal is not sinusoidal. It is because, the non-sinusoidal signal will have many other frequency components other than its normal frequency. Noise in ground also will affect the readings.
The best way to measure the frequency is by finding the time period and taking its inverse

3. DMMs can measure only the rms value of a signal. Its not the peak value. In scopes you can see the peak voltage. It depends on your requirement that which equipments should be used. If you want peak values use scope and if you want rms, use DMM...

- SUjO

using oscilloscope measure mains

Can we measure the AC mains 230Vac from the wall,
using oscilloscope?
I have tried it once, but the room circuit breaker breaks.
I still cannot figure out why?

Best Regards,
Siong Boon

measuring mains with an oscilloscope

No you cannot measure the AC mains directly on an oscilloscope, because of the common ground/earth of boht the mains & oscilloscope. This is why the circuit breaker breaks.
solution is to use any isolation transformer to isolate the AC mains input from oscilloscope.

how to measure frequency of noise signal on a cro

mirriyaz said:

No you cannot measure the AC mains directly on an oscilloscope, because of the common ground/earth of boht the mains & oscilloscope. This is why the circuit breaker breaks.
solution is to use any isolation transformer to isolate the AC mains input from oscilloscope.

Click to expand...

i didnt' understand your reply very clearly............ how the circuit breaker breaks when there is common ground/earth..........? i m new to this field , please reply in simple language.....

thanks in advance

using an isolation transformer & oscilloscope

use this link.might be usefull.

https://www.tek.com/Measurement/App_Notes/60_18324/eng/60W_18324_0.pdf