What should I look for in a used Oscilloscope

FreeEMS topics that aren't specific to hardware development or firmware development.
comrade904
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What should I look for in a used Oscilloscope

Post by comrade904 »

I want to help, so I am looking for a scope. I don't really know the difference between one that will work for you guys are doing, but mainly automotive signals and triggers. I THINK I might know but I like to assume I don't until I KNOW otherwise. So let me know any input you have or if I am on the right track... or if I am NOT on the right track please LET ME KNOW.

EX. 60 tooth trigger at 1 rpm is 60X1=60
60 at 1000 rpm is 60X1000=60000
60 at 7000 rpm is 60X7000=420000

So 420000 times a minute would be 420Khz?
I would probably need a scope and probes that was rated for at least 500Khz or 1Mhz right?

Then there is calibration. If it has a built in calibration signal, I wouldn't need to send it to anyone for calibration right?

There is a heathkit local to me on ebay here:
http://cgi.ebay.com/Vintage-HeathKit-Os ... 1|294%3A50
I hear they are easy to repair if there is something wrong. If I can't fix it or it isn't fast enough, I'm only out 35 dollars.

But my local used electronics place has a pair of HPs that are I think 10Mhz for 75dollars each. They have self calibration generators.

Or should I pass both up? I mean I know pretty much any NEW scope will work, but damn, new ones are too much.

Thanks guys
Oskar
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Re: What should I look for in a used Oscilloscope

Post by Oskar »

I don't know much about scopes but I have a quickie for you though.

A Hz is 1/s.

So 60 pulses per revolution * 9000rpm would be 540k pulses per minute, 9000 per second, so 9kHz.

For quick short pulses like that you probably want at least around 20-100 times the sampling speed of the actual pulse amount, so I would say 180kHz to 900kHz sampling speed.
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Fred
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Re: What should I look for in a used Oscilloscope

Post by Fred »

What Oskar said! + 2 channels so you can sync on one thing and view another ;-)

Good on you!

Fred.
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jetjockey
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Re: What should I look for in a used Oscilloscope

Post by jetjockey »

If you just want something to "look" at signals with, try WinSCOPE. Its a program that uses your computers sound card. The limiting factor is the sampling speed of the card, most are capable of 48kHz. Anything below 15kHz will show up just fine.
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Fred
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Re: What should I look for in a used Oscilloscope

Post by Fred »

Agreed, generally that does a nice job, I was using the linux version for a while and will be again before too long :-) There are some screenies in the diyefi photobucket account somewhere and a thread with them posted up.

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comrade904
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Re: What should I look for in a used Oscilloscope

Post by comrade904 »

Thanks for the advice!!! I thought my math was wrong, but it was late so I was more interested in going to bed. I am going to check discount electronics surplus in Arlington and see if I can find something good. Thanks again!!!
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Re: What should I look for in a used Oscilloscope

Post by deviousKA »

My advice would be to stay away from the vintage oscilloscopes if possible. If something breaks or falls out of calibration, you can easily be out of luck.

I have a circa-1985 tektronix 475 military version, it is built well and still works, but the variable timebase is off, so its basically worthless aside from 2 channel comparisons. I was in the same situation as you (needing a scope for general automotive use), buying the tek was a mistake.

Like that heath you posted, yeah there are still parts available, but all are recycled (used). As with anything 20+ years old, its going to be worn out.

Go pc-based, picoscope or a cheaper asian alternative. The less moving parts the better (imho)
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Fred
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Re: What should I look for in a used Oscilloscope

Post by Fred »

The less electrolytic caps the better OR the better quality the electros the better. They are one of the bigger reasons for electronic failures over time due to drying up.

Not very practical advice, but pretty true. The asian (assume you meant chinese, not a good make) ones are likely to have crappy caps in them which will let them down in the long term.

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jharvey
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Re: What should I look for in a used Oscilloscope

Post by jharvey »

Here's a company that lists quite a few of the lower cost options. I personally not a huge fan of the USB versions that require a PC. If you've already got a lap top it's not the bad, but I don't want to buy a lap top just for a scope. The crap top I've got I'm sure it to old and crappy to handle any of the USB scopes.

http://www.saelig.com/
comrade904
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Re: What should I look for in a used Oscilloscope

Post by comrade904 »

All they had, as usual was broken, old and overpriced!!! I'm not gonna pay $150 dollars for a broken scope when the Fry's has a new one for 315.
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