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measuring rise time percentages 10%-90%

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Walters, let's say I was born in 1945 and lived till 2030. How old was I when I have spent 30% of my lifetime?

No offence, but we need to ascertain that you got your elementary maths right first. Because I have resolved that the only way to help you out is not to tell you the solution, as they are almost always ignored, but ask you the questions instead.
 
But Rise time percentages are different values than
Time constant percentages

Rise time 10-90% percentages
Time constant 10-90% percnetages are different
 
When i Probe a Time constant or a Rise time i can't really tell the difference which is which on the oscilloscope they both look the same
what is different from a time constant VS a rise time?

How can i tell the difference on the oscilloscope?
 
YOU CANT!!!!!!!


all a scope does is shows you a waveform!!!
what infomation you want depends on what you measure.

just measre the bloody voltage and find at what time it reaches 10% of its mean maximum voltage!!!

then measure the time it takes to reach 90% of its mean maximum and take the bloody time difference


I and others have gone over this many times, it really isnt that hard
 
walters said:
When i Probe a Time constant or a Rise time i can't really tell the difference which is which on the oscilloscope they both look the same
what is different from a time constant VS a rise time?

How can i tell the difference on the oscilloscope?

The reason you get a rise-time on a signal is due to capacitance (inductance and sourcing capability) in a circuit.

A time-constant is more specific to a capacitance charging curve. It still is a rise-time, but rather then 10% to 90% a time-constant (todo with Capacitiance) is 0% - 67%

As I said, its just interpretation to govern what you want to display the resutls as.

IF you are looking at a capacitor they getting the time to 67% might be what is required, but if you are looking at the output of a logic chip the "rise time" might be what you are after


just step back, think about what percentages, go do some y = mx + c graphs and then have a look at a scope with a signal on

what is this to do with btw?


most scopes have a variable trigger point, my one advice would be to move the trigger point such that the signal is at 10% of it voltage at one of the gritcules on the scope screen, that will make measuring time alot easier
 
Look carefully at what you have. One of my TEK scopes
(454A) has the dotted line at 10% over the major, the
other (475) has the major at 10% and the dotted line as 0%.
Not a big deal, since using either one either way is close
enough, most of the time. :)
<als>
 
ha beat me to it, I just finished writing this
 

Attachments

  • risetime.pdf
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A time-constant is more specific to a capacitance charging curve. It still is a rise-time, but rather then 10% to 90% a time-constant (todo with Capacitiance) is 0% - 67%

Time Constant is 0%-67%
Rise time is 0%-90%

When i put my probe on a capacitor to see the time constant it looks like
a Rise time i can't really tell the difference between rise time and a time constant they both look the same
 
just measre the voltage and find at what time it reaches 10% of its mean maximum voltage!!!

I still don't know where 10% ,20%,30% etc i have not dotted lines
so how can i take the voltage and time from these percentages when i don't know where the percentages are my oscilloscope doesn't have a
percentage guide or graph on my display so im just guessing sorry
 
walters said:
just measre the voltage and find at what time it reaches 10% of its mean maximum voltage!!!

I still don't know where 10% ,20%,30% etc i have not dotted lines
so how can i take the voltage and time from these percentages when i don't know where the percentages are my oscilloscope doesn't have a
percentage guide or graph on my display so im just guessing sorry
Does your oscilloscope screen have a graticule (grid)?
 
walters said:
It have 8 cubes/divisions/gradules across
The whole point of having a graticule is to measure voltage and time. You don't need the little dotted 10% - 90% lines. They are just an aid. If you can't convert divisions on the screen to voltages, and then calculate percentages, I'm afraid you need more help than you can get here.
 
graticule is to measure voltage and time.
Yes i know how to do this

But how do i get the percentages and know where they are on the
oscilloscope display when im looking at a time constant or rise time
 
walters said:
graticule is to measure voltage and time.
Yes i know how to do this

But how do i get the percentages and know where they are on the
oscilloscope display when im looking at a time constant or rise time
Styx's PDF explained it all. I suggest you take up art or teeter-totter.
 
Can you please give me an example of measure percentages please
so i can understand it more i need examples
 
That is in my PDF

downloads fine for me, will upload to my FTP, but will only be tehre for 24hours


**broken link removed**

REad that and it explains everything
 
Thanks alot styx for doing this for me that was a great PDF file

Do i do the same thing for the Time constant? just like this pdf?
 
Styx said:
A time-constant is more specific to a capacitance charging curve. It still is a rise-time, but rather then 10% to 90% a time-constant (todo with Capacitiance) is 0% - 67%
 
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