Hi everyone I'm looking how to find time of a sine wave

Status
Not open for further replies.
S

Scottywatt

Member
Location
Mass
Occupation
Electrician/ Construction
They ask this on the exam in mass they only had a square box with a full wave with nothing Else in box; but on the bottom of the box which I couldn't read it was too small they had what looked like cm/.011 or something to that defect they ask at the half way point what was the number and then again ask another question asking other questions answers that jumped out at me which they had 4 was 10 and 5 So I picked 5 Didn't do anything like that in training so I don't know Thanks


Sent from my iPhone using Tapatalk
 
Scottywatt said:
They ask this on the exam in mass they only had a square box with a full wave with nothing Else in box; but on the bottom of the box which I couldn't read it was too small they had what looked like cm/.011 or something to that defect they ask at the half way point what was the number and then again ask another question asking other questions answers that jumped out at me which they had 4 was 10 and 5 So I picked 5 Didn't do anything like that in training so I don't know Thanks


Sent from my iPhone using Tapatalk
Click to expand...
It is called a sine wave, rather than a sign wave.

Sign refers to whether a number is positive or negative.

Sine is the trigonometry function, that is the basis for the simplest of waveforms. Electrical power grids are based on Voltage being a sine wave function of time, that we call alternating current. Play with the function sin(x) on Wolfram Alpha to understand some properties about this function. Play with the general equation for a sine wave of y=A*sin(B*x + C) + D, to understand how adjusting A, B, C, and D affect the shape and position of its graph. Also play with its inverse function, called arcsin(x).

I also recommend familiarizing yourself with the angle unit "radian", since this unit is often the preferred angle unit for studying sine waves.

I cannot understand the rest of your question, but hopefully by knowing to look for this by the term "sine wave", it can help you know how to research it further.
 
Last edited:
They didn't have anything on there that I could see but they were asking how much time Div/.011 something like that no other information other that the answers Don't know why they would be asking this on a journeyman's test


Sent from my iPhone using Tapatalk
 
Scottywatt said:
They didn't have anything on there that I could see but they were asking how much time Div/.011 something like that no other information other that the answers Don't know why they would be asking this on a journeyman's test


Sent from my iPhone using Tapatalk
Click to expand...

This might be in reference to reading an oscilloscope. The scope display is marked in divisions in the horizontal and the vertical. The horizontal is the time domain, and the vertical is the quantity you are measuring as a function of time, usually voltage.

You will configure your scope with a number of Volts per division, and milliseconds per division (or divisions per second), in order to represent the waveform on the screen. Older scopes only had the divisions as the grid it would show, and you'd have to cross-reference it with way you configure the Volts per division and divisions per second, in order to interpret it quantitatively. Newer scopes can mark out the Volts and milliseconds (or seconds) to show a graph of the waveform with context.
 
And knowing this will help wire houses I'm pretty sure not It anyways I don't know what you are talking about


Sent from my iPhone using Tapatalk
 
Scottywatt said:
All impressive but useless for everyday application


Sent from my iPhone using Tapatalk
Click to expand...
If it were useless, there wouldn't be a reason for inventing the oscilloscope.

Whether it is useful to you will depend on what scope of work you do (no punn intended). You probably wouldn't come across this in residential work, where a standard AC multimeter will usually suffice, but in a commercial application, one might be using an oscilloscope to diagnose power quality, or to determine if a component that runs on AC power is functioning properly. A lot of non-linear loads can distort the shape of the waveform from the original sine wave. You also have phase shifts from components that have a non-unity power factor, like motor loads, and the oscilloscope can measure those phase shifts.

Here's a visual to show what I mean. The scope is configured for 5 Volts/division, and 0.5 milliseconds/division. Divisions refer to the major gridlines. From measuring the screen, you can see a peak-to-peak amplitude of 5 divisions, and a crest-to-crest period of 2 divisions. From this information, you can calculate that it is has a 12.5V amplitude (8.8V nominal voltage), and a frequency of 1000 Hz.
2120C_front_lrg.jpg
 
Wow That's a lot to learn and if they ask different frequency or whatever I don't know if I could do it Sounds like you would have to take a class on that alone and I don't know anyone that does that regular instructors only touch on the different loads and what they look like Even with the information you have there which is helpful I couldn't really do anything in there box with the wave there were no grid lines there wasn't a zero reference or anything But thank you


Sent from my iPhone using Tapatalk
 
On top of that I don't know why they would ask or e spect a journeyman electrician to know this on the practice portion of the exam I already passed the code portion


Sent from my iPhone using Tapatalk
 
Scottywatt said:
Wow That's a lot to learn and if they ask different frequency or whatever I don't know if I could do it Sounds like you would have to take a class on that alone and I don't know anyone that does that regular instructors only touch on the different loads and what they look like Even with the information you have there which is helpful I couldn't really do anything in there box with the wave there were no grid lines there wasn't a zero reference or anything But thank you


Sent from my iPhone using Tapatalk
Click to expand...

I also worked as a teaching assistant for a class that taught students to use an oscilloscope and other instruments to build, analyze, and debug electronic circuits. Once the scope was introduced with the background of waveform terminology, students had a problem to start each class session to examine the oscilloscope and determining the specs of a mystery waveform.

As practice to learn the basics, take the sample scope picture I linked. Determine what A, B, C, and D would be, in the general equation of the voltage waveform V = A*sin(B*t + C) + D. Graph it on Wolfram Alpha or a graphing calculator, to see how it is consistent. Play with the constants A, B, C, and D to see their effects.

Answers:
A = 12.5 Volts
B = 2000*pi rad/sec
C = +pi/6 rad
D = 0 Volts
 
That's great so with a blank box with a full wave there is no way to figure half way point


Sent from my iPhone using Tapatalk
 
Scottywatt said:
That's great so with a blank box with a full wave there is no way to figure half way point


Sent from my iPhone using Tapatalk
Click to expand...
If your remit is to wire houses and just that do you need to/want deal with sine waves? Or half sine wave?
So what is it you actually want to find?
 
Scottywatt said:
All impressive but useless for everyday application


Sent from my iPhone using Tapatalk
Click to expand...
Not if you want to grow in your field.
it took me 19 years to go back and get my BSE, but it was worth it.
I started in construction and saw little value in the higher mathematics until I wanted to expand my knowledge base to get better pay, and quite honestly, a better electrical understanding. There’s more to electricity than listening to the boss and wire houses like he tells you to.
Just ask many on here that wire houses. The more they know the more valuable they become. There’s some pretty sharp people here that wire houses that understand Sine waves.
Troubleshooting sometimes takes a higher understanding of what’s going on….
 
I think you are missing the point there not giving any information I don't need at this point to learn all about sine waves they don't teach journeyman these things and I would like to pass the second half of the test I don't have the luxury of learning every aspect at this point it takes too much time no one seems to have the answer


Sent from my iPhone using Tapatalk
 
Scottywatt said:
No one seems to have the answer
Click to expand...

The reason no one seems to have the answer, is that none of us have the complete question. The most I can do is show you how to answer similar questions, from the information it sounds like you were given.

Even if you don't have the exact numbers that were given, you can make up your own example. But we need to see the substance of the question that was asked, in order to show you how to get an answer. Sketch what the illustration you were given looked like, give examples of numbers & units that you were given, and tell us the term you were asked to find. From that information, maybe then we can show you how to answer the question.

Maybe you could ask the creators of the test for an copy of this particular problem, or an equivalent problem that you are permitted to share.
 
Scottywatt said:
I think you are missing the point there not giving any information I don't need at this point to learn all about sine waves they don't teach journeyman these things and I would like to pass the second half of the test I don't have the luxury of learning every aspect at this point it takes too much time no one seems to have the answer
Click to expand...
I agree that this is useless question for a journeyman's exam.
 
Status
Not open for further replies.
Top