# measuring rise time percentages 10%-90%

Discussion in 'General Electronics Chat' started by walters, Aug 1, 2005.

1. ### waltersBanned

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So what's 30%? Given the range (-1,6)? == 1.1volt

2. ### heathtechNew Member

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Again, i apologize to Styx and Checkmate for going into an off topic subject. Maybe we are all three sufficiently picking Walter's brain to the point he can learn to REASON these problems out himself!

3. ### waltersBanned

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So a fuse has no POTENTIAL DIFFERENCE

A resistor has Potential differences

What is potential differences really ?
because i always thought potential differences was about + and - voltages
what is more positive from one side of a componenct from the negative side

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5. ### checkmateNew Member

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All right, let's now translate the problem onto the oscilloscope. An oscilloscope has voltage on the vertical axis, time on the horizontal.
Here comes the question. You see a slope on the oscilloscope. On the vertical axis, this slope rises from 0.5 divisions to 4.8 divisions.
Now, tell me how many divisions is the 20% point? And how many divisions is the 80% point. I repeat, the range is now (0.5,4.8).

6. ### heathtechNew Member

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Well, yes and no, with regards to defining potential difference. Remember, in Atlernating current, the negative and positive sides flip back and forth at a certain frequency (50/60Hz in the case of line voltage) So, a more universal way of saying it is that potential difference is the electrical pressure applied to a component, and the delta, or difference from one side of the component to the other, regardless of the polarity, is the voltage drop across the component. Think of a balloon with 5 PSI of pressure inside it. This PSI measurement is made with respect to ATMOSPHERIC pressure, or the pressure of ambient atmosphere. There is 5 pounds of potential force stored inside that balloon. If that air is released, the equivelant of current starts to flow (air current) If the hole through which the air is flowing is wide enough, it is metaphorically speaking like a switch, a wire, or a fuse, because there is nearly zero resistance to current flow, and the POTENTIAL drops to nearly zero. But, if the hole is very NARROW, it presents a resistance to the current flow, and it acts as a resistor, so the POTENTIAL is still measurable, just like a voltage drop across a resistor.

7. ### waltersBanned

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tell me how many divisions is the 20% point? And how many divisions is the 80% point

20%= .8 divisions
80%= 3.44 division

im taking a guess sorry

8. ### StyxActive Member

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never guess.
Assumption is the mother of all ****-ups.

if your boss wants to know those levels, you tell him what they are , not what you think

9. ### waltersBanned

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So did i get it wrong

10. ### checkmateNew Member

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I'm sorry. My wrong. I did not notice that a smiley was placed in the question. Try again. It's exactly the same question as before, only that some values are changed.
Remember, Given a (X1,X2) range, the Y% value is at
X1+[(X2-X1)*(Y/100)]

11. ### heathtechNew Member

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It is very late and I have to call it a night, but I do want to tell you Walters that I am impressed with your DESIRE to learn. I think any teacher would be glad to have a pupil who really thirsts for the knowledge the teacher can share. I can see that you have the ability to reason problems out, but it is difficult to have confidence when you are trying to teach it to yourself. I have spent many many hours in self study, but I also spent several years aquiring practical experience in variuos jobs, and I went to school in the military. A hands on training course is really essential if you want to get proficient, and succeed in this field. This forum is a great suppliment to learning, but if you want to keep your job you will seek some formal schooling with hands on curriculum.

12. ### waltersBanned

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Range is 4.3 divsions total

4.8 divisions minus 0.5 divisions= 4.3 divisions range

4.3 divided by 20%= 0.86
4.3 divided by 80%= 1.25

13. ### checkmateNew Member

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I've given you the equation. Now I'm telling you X1=0.5, X2=4.8, Y=80.
Now, what is the value?

14. ### waltersBanned

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Formula:
X1+[(X2-X1)*(Y/100)]

X1=0.5, X2=4.8, Y=80.
Now, what is the value?

4.8-.5= 4.3

80(Y) divided by 100= 0.8

4.3*0.8= 3.44

3.44 + 0.5(X1) = 3.94

15. ### checkmateNew Member

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Correct! Now, back to the original question. How many divisions is the 20% point and 80% point?

16. ### waltersBanned

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Can your guide me to know how to solve for this im not sure how to
do this or solve this answer really can u give me hints or steps
thanks for helping me out of this stuff

17. ### checkmateNew Member

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You have already solved the 80% point. Is it so hard to solve again for the 20% point? I already said, don't expect answers from me because there are none.

18. ### waltersBanned

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4.8-.5=4.3

20(Y) divided by 100=0.2

4.3* 0.2=0.86

0.86+0.5(X1)=1.36

19. ### checkmateNew Member

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All right, now if the sweep time (x-axis) is set at 20us/division, how much time does 4.6 divisions represent.

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92us

21. ### waltersBanned

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20us X 4.6= 92us