Use an oscilloscope to collect optical spectral data----make money online

I'm using my new Tek oscilloscope to collect data from a DIY spectrometer.  The scope is in X-Y mode with infinite persistence.  The X axis is controlled by the rotational position of the diffraction grating in the spectrometer, and the Y axis is controlled by the photomultiplier tube, which is detecting the spectra.  In this video, I discuss the scope setup, and in future videos, I will talk more about the spectrometer, and how to use it.

hey everyone I wanted to show you how

I'm collecting optical spectra data with

my new oscilloscope so here we have a

spectrometer that I just finished

building today and I'll talk about this

more in another video so I'm just going

to go over it really briefly now and

then spend most of the time talking

about the scope setup I have a compact

fluorescent bulb here wrapped in foil

just to keep it from being too

distracting and it's shining its light

through a slit that I made with two

razor blades on the inside of the

spectrometer housing and then there's a

diffraction grating here it's actually a

concave diffraction grating and it's

mounted on a rotating post and the post

is connected to this potentiometer and

then on the output there's another slit

made with two more razor blades and

inside here there's a photomultiplier

tube and a little power supply for it

here so if I turn the diffraction

grating slowly it doesn't take very much

i've only turned it maybe about ten

degrees there we can see the optical

spectra appears on the scope and it's

really spiky like this because it's a

mercury vapour lamp it's a fluorescent

with some phosphors to bulk out to sort

of make the spectra more pleasant to

look at so the idea here is we're using

the oscilloscope is sort of a data

logger and it's in XY mode and the x

axis is controlled by the voltage coming

out of this potentiometer

and the y axis is controlled by the

voltage coming out of the

photomultiplier tube and I have

persistence on and set to infinity so as

I scan across it keeps the spectra on

screen I ran into an interesting problem

with the scope setup in XY mode the

scope is still triggered like it

normally is in time-based mode but the

as Dave Jones on the eevblog pointed out

at these tech scopes if they don't have

a trigger they default to something

pretty slow like 10 Hertz or 30 Hertz or

something like that and for this

application that's not going to work

because as I'm scanning along the signal

is changing quickly enough or you'd have

to scan really slow to make a 10 or 30

Hertz update rate work

so what I did was I turned on the

arbitrary function generator and set it

to about 10 kilohertz and then plugged

the function generator input into

channel 3 and set up the trigger to

actually be on channel 3 so this way we

can dial the trigger frequency of the

scope up and down with the function

generator and then you can see the

trigger frequency is reading out to be

exactly 10 kilohertz there so that was a

pretty cool feature I mean it's actually

kind of nice to be able to set the

trigger frequency when it's freerunning

I imagine that would actually be pretty

handy for other applications too anyway

so then in aquire mode I also set this

to high-res mode so right now it's

sampling at two-and-a-half mega samples

per second and since the you know the

signal is not changing very quickly from

this photo multiplier to what I really

want is to get rid of the noise that

would be inherent in this signal so in

in snort this normal sample mode check

out what that looks like

oh my light rolled away here we are as

you can see it's not even close to the

same thing there's so much uncertainty

in the measurement that the scope is

making the trace rather fat so in

high-res mode when we scan along it's a

much easier to see it's the the

triggering setup is much more

appropriate for the type of data that

we're getting you can also use the

average mode so the way I understand

this is in average mode it will take a

sweep and then in this case it's set to

16 so it'll actually take 16 sweeps and

average the traces altogether I'm not

exactly sure how that works in XY mode I

tried it here it will turn it on and as

you can see it's a nice sharp trace like

it is in high-res mode however if I scan

it quickly the trace is not overlapping

because I'm moving quickly enough where

the averaging is becoming a problem

so in high-res mode I believe what's

happening

is even though it's running at

two-and-a-half mega samples per second

it's actually averaging like point by

point so as it goes along it's averaging

as it's taking data as opposed to the

average setting which takes an entire

trace and then tries to average it with

the subsequent 15 traces so in this mode

it's it's snappy enough where I can roll

back through it and it almost traces

over itself this is actually probably

mechanical slop in the system and we're

not getting quite the same spectra

because this light ball rolled out of

the way there we go so if I clear the

persistence there it Rebekah's something

halfway decent looking

since the potentiometer has to be DC

coupled into the scope in order to read

out the position and it's a relatively

small change in fact this is like a

hundred and twenty degree pot but even

still we're only turning it like ten or

twenty degrees so we're not getting much

swing in the signal and if I just used a

zero and five volt for example supply on

the pot the voltage would be centered on

two and a half volts and the scope would

have a tough time dealing with that

because we're really only interested in

you know one voltage swing centered on

two and a half or even less than that

and to get around this problem I came up

with a bipolar supply so that the pot is

actually pretty close to zero and then I

can use almost no offset on the scope

and still get a pretty good signal still

zooming in on the part that we want to

look at the y-axis is currently set at

one volt per division so this is

actually you know about a

one-two-three-four almost a five volt

signal to the peak here and the way that

I'm controlling the gain of this is by

controlling the voltage to the

photomultiplier tube the output of the

photomultiplier the anode has a 100k

resistor going to ground so a 10 volt

signal there would correspond to a

hundred micro amps of anode current

which is the maximum for this photo

multiplier that's handy because then I

can always tell if the signal is getting

close to 10 volts that means I there's

too much gain and right now that I'm

putting in about 6 volts into this power

supply which means I should be getting

about 600 volts out and that's about the

bottom range for this photo multiplier

there stated or the rated voltage is

about 1500 and I think I'll get probably

two maybe three or even four orders of

magnitude more gain at 1500 volts so in

other words this spectrometer can be way

more sensitive than it currently is

so it's handy to be able to do a screen

capture and just grab this spectra

that's that's useful what would be even

nicer is to have this in data in the

computer and the way I'm going to do

this is to set the scope to sweep slowly

not in XY mode but just in time base

mode and record two traces set it up

maybe so that it's about half a second

per division or something and that will

give me enough time to sweep through the

whole spectrum then we can just save

those two waveforms to thumb drive and

import them on the computer and then

plot the one channel against the other

and I'll show that in a subsequent video

okay see you next time byeTop Search Keyword : online earning, , make money online, earn money online, online earning, online earning sites, make money online free, online money income, earn money online free, money online, best way to earn money online, online income site, money earning websites, best online earning sites, easiest way to earn money online, earn money payment bkash, online money income site