.56 seconds and .28 seconds time measurement on an analog oscilloscope

[Reloadron]

s

Well how did you calculate this tho? 500mS X 10 divisons on the 0-scope = .1 sec sweep speed?

Well Billy as I mentioned, there is no formula. Let's say I have a 1 KHz square wave I want to display on my scope. Well I know that Time and Frequency are reciprocals so the time for 1 KHz is T = 1 / F so 1 / 1000 = .001 Sec. (1 mS). Well if I set my scope up for 1 mS / Div and I have 10 horizontal divisions I will have one repetition of my wave form per division and display 10 repetitions on my screen. If I really want to see and measure my waveform it is hard to view only one with 10 on the screen so maybe I'll stretch it out a little and use a faster sweep. I can move to .5 mS / Div so now my 10 divisions represents 5 mS. I should see 5 repetitions of my 1 KHz signal. Good but not good enough, I want to better see 1 repetition. I now set my sweep time to .2 mS / Div. Now my 10 divisions represents 2 mS. I should see 2 full repetitions of my signal. Finally if I set my sweep speed to .1 mS / Div my whole 10 divisions should represent 1 mS. I should see one full complete repetition of my 1 KHz signal. The problem is that if my 1 KHz is actually 950 Hz then my time becomes 1/950 = 1.05263 mS so my single repetition will exceed my 10 divisions that I can measure.

If my sweep setting is for example 5 mS / Div I know I have 10 horizontal divisions so my entire sweep represents 10 Div * 5 mS = 50 mS.

There is no formula to determine the ideal sweep speed setting. The scope is a tool and like any tool it can do many real nice things. However, also like any tool you need to understand it and learn how to use it. You also need to know its strong and weak points. There is no formula to tell you, for example, that when looking at low frequencies to use DC coupling, you learn that. I suggest you watch rumpfy's link and try a Google of Oscilloscope Basics to learn more about scopes.

Ron

 

[Billy Mayo]

Ok Thanks

low frequencies to use DC coupling on triggering

Why do I have to use DC couple on the trigger? What does DC couple do for Low frequency's?

 

[Reloadron]

For low frequencies, the old rule of thumb was below 50 Hz but that is not gospel, you want to use DC coupling for the signal input and the triggering.

Here is a little video on the subject.

Ron

 

[Billy Mayo]

for low frequency you want to use DC coupling for the signal input and the triggering.

Any Reason why?

 

[Reloadron]

Any Reason why?

Yes, when using AC coupling the signal is coupled through a capacitor. So looking at a common scope I may see 1 M Ohm input shunted by 25 pF so my signal runs through a 25 pF cap and across the 1 M Ohm input. What happens if I try and pass a 5 Hz. square wave through that network? It sure won't look like a square wave when it gets to the other side of the input. It will be distorted, real distorted.

Ron

 

[Billy Mayo]

But why does the triggering need DC coupling tho?

 

[rumpfy]

If you have a repeating waveform that lasts for 0.28 seconds, and if you wish to see two complete cycles, then the time required to see two cycles is 0.56 seconds.
An oscilloscope generally has a display which is 10 cm wide and that is 10 divisions. So, if you want to see 2 cycles of a waveform, then the horizontal sweep time is 0.56 seconds for 10 divisions or 10 cm. That works out to 0.056 seconds PER DIVISION. The timebase speed setting would then be 56 milliseconds per div. Because 56 ms would not be available but generally 50 milliseconds would be, you set the time per div switch to 50mS/div. You would see nearly two complete cycles so if you changed the time/div switch to 100 mS/div, you would see 3.57 cycles. If you wanted to see an exact number of cycles, you could adjust the 'FINE' knob to get the required number of cycles displayed.
Seeing all of this requires that the horizontal trace is 'synchronised', so that with each successive horizontal sweep, each successive display is positioned exactly on top of the previous display. This need brings up the ugly subject of 'triggering', and, how to achieve it.
Has this answered your question raised in post #19?

 

[crutschow]

s

Well how did you calculate this tho? 500mS X 10 divisons on the 0-scope = .1 sec sweep speed?

You math is a little off. 500ms (0.5s) x 10 divisions = 5 sec sweep speed for one sweep. 50ms x 10 divisions = .5s sweep speed.

 

[Reloadron]

Any Reason why?

I suggest you give this a read as to O Scope basics including triggering. Being a tool as I mentioned O Scopes have features. Some more than others. To correctly use a scope you need to be familiar with the scopes operation and features. There is no way I can cover O Scope operation in detail or even triggering in a few paragraphs.

Ron