how recognize the wave start point...

[dr.power]

Hello friends.

I just got a question.
How a measurement device like a scope recognizes the Sine waves from Cosine waves? I mean as soon as you connect the prob of a scope to a cosine wave the waveform becomes like a cosine having its "Max" domain at the zero for reference point or for a sine wave for instance the scope recognizes that at zero or reference point the waveform is a sine having the domain value of "zero"?
How a scope recolonizes the reference point for a waveform? The frequency is the number of perfect cycles per one second. If a scope measures the cycle of a wave for one second there is nothing to guarantee that the start point has been exactly the start point of the waveform itself (for instance the maximum value for a cosine wave).
The same question for 2 square waves having 90 degrees out of phase.
Hope it makes sense to you!

Thanks

 

[crutschow]

Whether it's a sine or cosine is just a matter of phase reference. If you are only looking at one signal then there is no relative phase reference and a sine and cosine appear the same. If you have one sine and one cosine, then it depends upon which waveform you trigger from and the trigger level as to what is the reference point. The scope doesn't recognize the waveform. It's reference is simply whichever waveform you are triggering from.

The same holds true for 2 square waves.

 

[Sceadwian]

It doesn't, you provide the reference point, this is why scopes have trigger modules. In the case of a complex waveform you're trying to measure the entire window of you would have to provide the scope with a trigger (externally applied voltage) that the scope synchronizes to. Many scopes have sophisticated trigger modules, but for practical scope use it's up to the actual user to supply the proper trigger signal to analyze the incoming signal.

 

[dr.power]

Whether it's a sine or cosine is just a matter of phase reference. If you are only looking at one signal then there is no relative phase reference and a sine and cosine appear the same. If you have one sine and one cosine, then it depends upon which waveform you trigger from and the trigger level as to what is the reference point. The scope doesn't recognize the waveform. It's reference is simply whichever waveform you are triggering from.

The same holds true for 2 square waves.

Thanks for your reply,
What do you mean by TRIGGER here? How to trigger?

 

[dr.power]

Actually my scope has a trgger output which generates a square 1kHz wave, But I do not know the usage for it?

 

[crutschow]

Thanks for your reply,
What do you mean by TRIGGER here? How to trigger?

Oscilloscopes have a trigger circuit that synchronizes the horizontal sweep with the waveform so that a stationary waveform is shown for repetitive signals such as a sinewave. The oscilloscope has adjustments for trigger level and signal slope (positive or negative slope) to select where on the waveform the sweep starts.

 

[ericgibbs]

Actually my scope has a trgger output which generates a square 1kHz wave, But I do not know the usage for it?

That output is a simple calibration signal for trimming scope probes, to correct their response, for over/under shoot on the square wave.

Also on some scopes its set at a fixed voltage, on mine its 1V., so that its a quick for the Yamp gains.