Recommend a Modest Scope

[bgavin]

The last scope I used was a Tektronix 475... IBM provided these to us as part of our tool assortment. Yes, it has been awhile.

Q: can somebody recommend a reliable (used) scope for general work?

I do audio impedance measurements, ripple, just basic stuff.

[willawake]

Re: Recommend a Modest Scope

no idea really, just know that the more mhz is better
perhaps a computer based one would be the cheapest solution?

[i4004]

Re: Recommend a Modest Scope

http://shop.ebay.com/items/_W0QQ_nkw...romZR40QQ_mdoZ

hameg is also a good company
http://shop.ebay.com/items/_W0QQ_dmp...+475&_osacat=0

usb scopes
http://www.picotech.com/oscilloscope...fications.html

if i was heavy scope user, i would have both used standalone unit, and new usb device...just to check one against the other..hehe...

[Krankshaft]

Re: Recommend a Modest Scope

I am pretty happy with my Tektronix 475 built like a rock and still ticking .

As for portability check out the USB scopes as suggested above you can plug them into a laptop and digitally save the waveforms. They're pretty cool.

They also make PCI cards if connecting them into a desktop is your thing.

[bgavin]

Re: Recommend a Modest Scope

Is a computer based scope bordering on the same uselessness as using a computer to view movies?

I have a basic o-scope function built into my TrueRTA Level 4 software that I use for loudspeaker measurements. I don't know if a USB sound card is smart enough to measure ripple, etc, but the software seems to think so.

[i4004]

Re: Recommend a Modest Scope

i would say it's quite the opposite; standalone scopes usually have small screens.
pcs have bigger screens, and that's better when you wanna view a waveform.
it's also usefull to store it(as image), and with pc that's easy enough.

i dunno if soundcard has bandwidth to measure stuff you need, then again audio overall is not that bandwidth hungry etc.
inspect help files and documentation for that software, to see what card would do...
todays cards do 96khz(or even more) sampling, and perhaps that would indeed suffice...

why did you mention usb sound card?
perhaps that in the machine already will do...

http://www.trueaudio.com/rta_abt1.htm
Time base ranges from 20mSec/Division down to 0.05mSec/Div.

my scope(which is 10mhz..i think..huh) goes down to 0.5usec

i would first try souncard and that sotfware..if it doesn't work get scope...old or usb..depends on money you wanna invest...used is cheaper, but it's used...heh

[i4004]

Re: Recommend a Modest Scope

usb scope recently mentioned here
https://www.badcaps.net/forum/showthread.php?t=6059

it's 200mhz scope for 350$.
http://cgi.ebay.com/200Ms-s-200MHz-D...QQcmdZViewItem
no way you can find such thing as standalone scope for that price...

[gg1978]

Re: Recommend a Modest Scope

We've got a few older HP 546xx series scopes at work, they're nice for being older scopes.. Probably more spendy than what you want to spend though...

[PCBONEZ]

Re: Recommend a Modest Scope

That old Tektronix 475 IS a reliable scope.
- Easy to get parts for too.

Thing is it's Analog and a DSO (storage) is better for things like ripple.
DSO will save a moment in time for you so you can analyze what's going on where as Analog just keeps refreshing the screen.
DSO is better for erratic traces like ripple.
Analog is fine for wave forms that don't change much.

Tektronix 485 is very similar to the 475 but is a DSO at 350Mhz.

If you want something newer look in the 24xx series.
Those were Tektronix's first series with actual microprocessors in them.
They sold zillions so they aren't hard to find.

Next after them was the TAS series which are still a bit pricey (usually).

20 MHz is just enough to see PSU ripple but like Willa said more MHz is better.
[I would go for at least 100 MHz.]
If you want to see ringing in MOSFETs you'd need a 1GHz scope. [And a fat wallet.]

There is not much that can break and no maintenance in a USB scope but on the other hand they can't be tuned or calibrated if they drift off the marks.

Many regular DSO scopes (even some old ones) have a feature/interface called GPIB that allows sending the waveform to a printer, plotter, or a PC.

.

[FIXITNOW]

Re: Recommend a Modest Scope

got mine of ebay just searched for nearest so could collect hitachi v-209 cost 10 english pounds

20mhz 2 ch does what i need

[bgavin]

Re: Recommend a Modest Scope

I have TrueRTA level 4 setup on my laptop for audio measurements. The interface is a high quality Edirol UA-25 USB type. For critical measurements, I use an external +48v phantom supply for the mic. Most of the time, the built-in phantom is sufficient. I'm only doing subwoofers at the moment, but will eventually do full range audio systems.

The primary need for a scope is for impedance sweeps. Ideally, I'd like to figure out how to use the O'scope function in TrueRTA for voltage sweeps. The UA-25 is full duplex, so it generates the signal on TX and measures it on RX. I use a PLX 3002 to drive the speakers.

The secondary use is for scoping computer power supplies (or boards) for ripple.

[i4004]

Re: Recommend a Modest Scope

>20 MHz is just enough to see PSU ripple

"just"?
psu ripple barely goes over 100-150khz...(depending on the switching freq.)
so something showing up to that would suffice.
jonnyguru ripple shots are taken with usb scope with a piss poor bandwidth.
and it's not a problem.

[Krankshaft]

Re: Recommend a Modest Scope

That old Tektronix 475 IS a reliable scope.
- Easy to get parts for too.

Not to mention it doesn't use tons of Large Scale ICs like Tektronix used on their other scopes in the 80s I considered before buying this one.

These ICs have since been discontinued leaving the owners of these scopes in trouble. Even if you are lucky enough to locate the IC you are looking for (won the lottery lately?) no doubt you will pay through the nose.

[PCBONEZ]

Re: Recommend a Modest Scope

Johnnyguru uses this:

which is just barely adequate for measuring SMPS ripple.
It's more intended for audio than anything else.

The 20M S/s sample rate is for REPETITIVE signals - like a pure sine or square wave.
For non repetitive signals like ripple it's sample rate is only 1M S/s.
That makes reliable/accurate to about 100kHz max assuming 10 samples/cycle.

Some newer PSUs have already upped the switching frequency to ~400kHz.
[So I read somewhere in a review of one of those 1000w-ish PSUs....]
I don't expect 500kHz to be a long way down the road.

If planning on keeping the scope a while then 5M S/s is probably a good minimum sample rate to look for.

.

[KeriJane]

Re: Recommend a Modest Scope

Thank you for the advice on Oscilloscopes.

I went and bought a Digital Storage Oscilloscope on eBay last week that's rated at 25M bandwidth with a sampling rate of 100MS/s, also noted as a "sampling rate range of 10MS/s-100MS/s". Primarily I bought it to use at work as there are 21 technicians there and only one old beat-up handheld Oscilloscope left over from the '90s and a REALLY old CRT scope from the '80s (only about 5 of us know how to use one or even what they're for)

Should this be adequate for measuring PSU ripple as well as the relatively low-speed waveforms that I observe at work?

The scope is an OWON PDS5022S. It seems to be an exceptional value, really almost too good to be true. The eBay link is: http://cgi.ebay.com/ws/eBayISAPI.dll...MEWN:IT&ih=003

It'll probably be here Wednesday or Thursday.... maybe I should hook it up to a cheapie PSU and see what it can do?

If anyone's interested I can follow up afterward. Maybe even post some screenshots.

Have Fun,
Keri

PS. I know just the basics about scopes and electronics. It shocks and appalls me that a business with 20+ "technicians" has only 5 that know anything at all about Oscilloscopes (2 of us are girls!) and that I, with my meager knowledge appear to be the "expert" on Oscilloscopes and Electronics in general. Can people (especially repair technicians) really be this lazy and incompetent?

[i4004]

Re: Recommend a Modest Scope

not everyone is interested in everything. and without interest there's no love, and without love anything one does looks lazy and incompetent.
so it's no wonder relatively few people will be good at this.
(and i don't think forcing people to do something really works...if he/she's not enjoying the work, he's not really good at it, and that's it..)

about scoping; i dunno will you see anything if you hook it up directly, with probes you'll get.
search jonnyguru forums for "scope" and you should end up with discussions about it....here
http://www.jonnyguru.com/forums/show...ighlight=scope
and
http://www.jonnyguru.com/forums/show...ighlight=scope
also
http://www.jonnyguru.com/forums/show...ighlight=scope
one more
http://www.jonnyguru.com/forums/show...ighlight=scope
(i didn't read that one)
http://www.jonnyguru.com/forums/show...ighlight=scope
(didn't read this one either)
to see images you need to register there.

thing; they use load tester and they hook up the scope on that. without proper load and with normal probes, i dunno will you see anything.
i know i didn't.

so it's kinda moot.

that scope seems good and it's pretty cheap.


yeah, sure...post some screenshots...of anything you like...

read this too
https://www.badcaps.net/forum/showthread.php?t=6059

oh yeah, stay safe while measuring...read manuals etc.

good luck

[PCBONEZ]

Re: Recommend a Modest Scope

i4004
No it's not a moot point.
The fact that it makes a display doesn't make what's on the display accurate.
A scope with too low a sample rate will still show a trace but it won't be a representation of the actual wave form in the circuit.
Quick sketch attached.

KeriJane
I looked at Owon scopes a while back.
Owon is a Chinese brand that's been around a while. (I think.)
Seem to have gone International with marketing their products just recently.
That one should do fine for ripple.
Hopefully they use good Jap caps or solid poly's in test equipment.
http://www.owon.com.cn/eng/index.asp
-
How about a little tech review on it after you learn it?
[I'm getting older and my Tektronix is getting heavier.]

.

[Gianni]

Re: Recommend a Modest Scope

The Owon scope resembles my TDS210.

Well 25MHz should be enough for hobby job and also to measure PSU ripple.
For sure it is not enough to make measurements with great accuracy when you are testing devices working with high DV/DT or if you are measuring spikes.
I use a Lecroy LT344 for job, it is a 500MHz DSO, and it can see more details on waveforms compared to my Tek.
OTOH I paid about 1.340€ in '96 for my Tek while the Lecroy was 18.000€ (IIRC) in 2001.
The only thing I hate of Lecroy is that Voltage/Time scale selectors are inverted respect to almost all scope I have used.

@ KeriJane: let us know your impression and results when you have done some measurements.
At least this scope has a color display, my Tek is monochromatic and i have to pay attention when I use 2 channels ( 2 times/year )

Ciao
Gianni

[KeriJane]

Re: Recommend a Modest Scope

Thank you for all of the interesting links.

Oh dear. They reminds me of: "The more you learn, the less you know!"
For one, I wouldn't have thought that those little grounding clips would be so much fuss.

But I'll get the idea eventually.

Anyhow, I'll review it as soon as possible. Please bear in mind that I'm only moderately proficient, so feel free to point out things that I'm ignorant of or just plain wrong about. I've already read the online PDF manual for it so at least I should be able to turn it on. I'm hoping that I didn't just buy a big box full of Teapos and Hermeis.

My first experience with a digital scope was disappointing as the sampling rate was apparently very poor. The CRT antique we have at work is one of these early digital ones and is practically useless. Even the handheld LCD scope from 1994 picks up more stuff.

At some point I'd like to obtain a good old fashioned "live" scope. Does anyone have any suggestions for something that isn't too cumbersome or heavy? Secondhand Hitachi scopes on eBay look promising...

Have Fun,
Keri

PS. Did you say "€18,000"? As in "Eighteen Thousand Euros"? Eep! That must be some Oscilloscope. I'm pretty sure that's about what my parents paid for their HOUSE! Cool!

[i4004]

Re: Recommend a Modest Scope

well, it's 500mhz, so....

i4004
No it's not a moot point.
The fact that it makes a display doesn't make what's on the display accurate.
A scope with too low a sample rate will still show a trace but it won't be a representation of the actual wave form in the circuit.
Quick sketch attached.

moot because she needs load tester.
we're not discussing jonnyguru's low bandwidth scope anymore.
ie try hooking the scope just to bare psu with probes you have...any ripple there?

did you make this sketch?
yeah, a good representation of nyquist theorem, ie what happens when you don't respect it, ie what aliasing is.
infact quite excellent...

gianni, where do you work, and what do you do?
500mhz got me wondering...heh