Slashdot Mirror
Oscilloscopes For Modern Engineers?
Every few years someone asks this community for advice on oscilloscopes. Reader dawning writes "I've just graduated with a degree in Computer Engineering (and did a Comp Sci one while I was at it) and I'm finding myself woefully under-equipped to do some great hardware projects. I'm in major need of a good oscilloscope. I'm willing to put down $2,000 for a decent one, but there are several options and they all seem so archaic and limited. I'm happy to use something that must be controlled through a PC if that gives me more measuring features. What would you, my esteemed Slashdot colleagues, get for yourself?"
I use an R7704 at home, and a 7633 at the office.
The determined Real Programmer can write Fortran programs in any language.
May I suggest you get a DAQ usb card and Labview from National Instruments. Probably some of the best investments you can do. You can do many things with a DAQ card and Labview including building your own digital Oscilloscope.
Without know what frequency range, voltage range, connectivity requirements (is computer connection USB or serial port?) I cannot help you in your selection.
OTOH you can give me the $2000 and I can give you my blessing.
I'm rather fond of the low-end Tek scopes. The LCD screen is a little slow, and there's only 2 channels, but these are not huge limitations for most basic work. I use these teaching physics and intro electronics to undergraduates - they're easy to use, lightweight, and can store data through USB or pen drives. 100 MHz for about $1200, which is OK for general use.
Building a Cheap Oscilloscope Using Your PC?
There are some interesting suggestions there.
I'm thinking that some of the more adventurous open hardware folks might think about working on a completely open hardware scope. I mean, what's better than being able to use open tools to build open projects?
coding is life
Got mine on ebay for a ridiculously low price... but like someone else mentioned, what you use it for is rather important.
Don't skimp. Get a good one, name brand (Tek, Agilent, LeCroy, etc.) at least 100 MHz bandwidth (the higher the better), 4 channels if you can afford it, some way to get data off the scope and onto a USB drive/network. Everything else is fluff and you can pay for it if you want, but I'd say the above are non-negotiable.
Don't even think about a PC-based scope. A scope is a standalone instrument, always has been, always will be.
I used to be a certified electronics calibration technician, and I've never noticed a difference between the analog and the digital.
If $2k is your budget, and not having any idea what you're going to be using it for, I highly recommend a handheld Fluke. They were just as reliable as the old analog ones, but with more features.
This is the model I'm referring to:
Fluke 125
Official Fluke 125 page
aero2600
Please stop hurting America -- Jon Stewart
its funny that electronics engineers throw out their broken electronics.
I'm an EE who does electronics design for a living, and I've done audio, SMPS, digital, FPGA, you name it. And in each case, the "best scope to use" was different:
- For analog work, or for simple microcontroller debugging, something like a USBee will work great.
- If you're doing higher speed analog, lower-frequency RF or switching power supply design, I'm a huge fan of the Tektronix DPO series. I use a TDS3032.
- For digital work (debugging serial/parallel interfaces and whatnot) I use an old 100MHz "Mega Zoom" HP logic analyzer.
- If I'm doing a design with a big FPGA, bringing lots of extra signals to the FPGA during layout time and using something like Chipscope Pro (on Xilinx FPGAs) to watch what's going on has been extremely handy. No test equipment required!
Not really.
If they need it accurate and traceable they'd have to pay a lab to calibrate it after it was fixed. Such a lab would reject it due to it being fixed (and charge a pretty penny with no calibrated scope at the end of the process.) So they're stuck.
(This reminds me of a story my wife tells about a lab PC that had a bad case of infant mortality. The local techs wanted to fix it themselves. She pointed out it was still in warranty - so the thing to do was send it back for fix-or-replace for free, rather than void the warranty and maybe end up with a broken machine and nothing (but wasted engineer time) to show for it.
Fixing a scope adequately for home use is another matter. Then, if you ever need serious accuracy, you can do the same sort of compensation hacks that were done back in the tube days, when stuff drifted all the time and you couldn't just have a lab tune up anything complicated and expect it to stay tuned.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
An employer. Seriously. Every piece of test equipment I've ever owned (some costing upwards of $5000 1978 dollars) was a lousy investment.
Especially when you consider that I have a lab at $WORK with scores of tools costing more than I make in a year, it's stupid to spend my own money on them.
Lacking <sarcasm> tags,
I've been engineering for over 30 years and in my opinion there's nothing like a good old 7000 series Tektronix scope. You can pick one up on ebay and configure it with modules to do just about anything you would want a scope to do. They're old, use some power and oh by the way...they are analog. But they are great scopes. A lot will depend on what the projects you are talking about require, but as a good general purpose scope they are great. You can get all the manuals and work on the equipment yourself. And you will see electronics build the way no one builds it anymore, including Tek. I have a complete bench full of Tek and HP gear and it serves me well for projects ranging from audio designs to the latest single chip controller applications. Good luck in your search.
... at http://gtalug.org/wiki/Meetings:2005-12, Peter demonstrated the virtual oscilloscope and virtual function generator applications, which are available as open source.
The hardware unit (approx 3 x 6 x 1" thick) is available at http://www.syscompdesign.com/CGR101.html
--dave
davecb@spamcop.net
The difference between a 'scope that is a joy to use and one that is useless and frustrating is triggering. Good triggering is what gives you ease-of-use. You can't see it if the 'scope can't trigger on it. This is especially true when you are trying to catch a glitch.
In my experience, Tektronix 'scopes have always been easier to use because they triggered better than the competition. We got a bunch of money once and decided to buy new oscilloscopes. Since we worked for the government, we had to write up a tender so there could be a fair competition. It drove us nuts. The specifications for the other brands were as good as those of the Tek 'scopes. We had used the competing 'scopes and hated them. We had to bend like pretzels to get a specification that would ensure that we got the 'scopes we wanted. The specifications just don't do a good job of describing how usable an oscilloscope is. (ditto for spectrum analyzers)
The Tek 'scopes were bullet proof. I could throw my 'scope in the back of a station wagon, drive to the airport, hop on a rented plane, fly five hundred miles, hike up a mountain and the Tek 'scope would ALWAYS work when I got to the job site.
These days, with digital 'scopes, a good test is to throw a nasty waveform at the 'scope and press the autoset button. If you're looking at something useful, the 'scope is good. If you're looking at garbage, the 'scope is garbage.
These days, I have an ancient Tek (circa 1970) 'scope on my bench at home. It works great for most of my home projects. At work, I have access to 'scopes that will do 1 GHz. My buds at the NRC have a 'scope that does 6 GHz. Somehow all the 'scopes are Tektronix.
Since I started in the industry in 1974, Tektronix has made the best oscilloscopes. Some of their other stuff is crap IMHO but nobody else can touch their 'scopes. I'm teaching college now and we prefer to buy as cheap as possible. Whenever we've tried something other than Tek, we've regretted it. The Tek 'scopes have the advantage of being student proof!
For other test equipment, I would choose other manufacturers. HP/Agilent would be my choice for almost everything else that isn't an oscilloscope.
Before plunking down good $$, I'd wait and see what sort of equipment is *really* needed. Scopes are a nice tool, but there are other tools like good spectrum analyzers (with waveform analysers) and other gear that can add up quickly. I'd say, let the need present itself, then invest to the need.
---- Teach Peace. It's Cheaper Than War.
I have a very nice, for me, rackmount 350MHz 4 channel Tek scope with some very killer plugins.
The scopes I used at work today are really beyond anything needed for home use, unless you're into some extremely expensive hobbies.
The portable scope is a 3054B; 500MHz x4 channels. (~$10k, with options) The good one is an 11GHz x2ch Lecroy ($ almost 6 digits), I made picosecond-order measurements with it today.
The differential probe was $5k each; (wasn't that what gov. spitzer paid? lol.) our newb has killed two. (4Vmax) $2k each to fix.
If you can afford it for home use, I'd recommend the Tek 3054 or a lower bandwidth cousin. They're very easy to use.
If you can get surplus scopes coming out of downsized companies, you can get a deal; that's how I got my rackmount and a stack of plugins for $130. It was a production fixture at a missle plant in the 90s. :)
Digital is great, as long as you realize the limitations; digital displays lie sometimes. If you're going to base a paper on it, use multiple measurements with different equipment. :) I've seen fresh engineers embarrassed by artifacts.
Truth isn't Truth - Guliani
One reason I mention these is because newer scopes, particularly the Tek 3000-series, while incredibly useful because of their size, weight, and connectivity (they have a linux-based OS that includes a webserver so you can plug one in with a cat5 and control it from your desk remotely: pure awesome!) are just about impossible to repair. Everything, *everything* is in custom silicon. On a LeCroy you can swap out the input amps if you burn one, swap out the timebase card or the A/D cards for each channel. It's like working with an old PC, as opposed to an ipod.
Also, budget for probes. Get probes rated for at least 1.5 times the scope's bandwidth: usually people ship probes that have the same bandwidth as the scope's max, but the spec on them actually means they're at something like -3dB and pretty fuzzy at that bandwidth. I got 500's for my 350mhz scope and they're beautiful. A lot of people sell broken probes and I've found, in the three I've purchased, that in every case it was a broken solderjoint where the probe cable met the board that attaches to the scope BNC. I reflowed it (no added solder for fear it'd mess with the tuning) and got three new probes for cheap.
There are people selling vintage scopes on ebay that have NIST certification, if that's important to you, but you can also get it independently certified if you need it. Newark.com has cal services, to my surprise. (They're who we use at work.)
I personally dislike Yokogawa scopes because their interface doesn't make sense to me. I can sit down at an Agilent or Tek or LeCroy and get it to do what I want pretty quickly (digital LeCroys are weird about horizontal offset) but Yokogawas I spend a lot of time reading the manual. But they're nicely engineered.
The USB scopes I've used were disappointments to me: the $ per mhz isn't competitive with a used scope, and they're typically pretty tied to the company software, which might not do what you want.
Nostalgia's not what it used to be.
If you're a C.S. person, it's likely that you are a digital person, and you will most frequently use the oscilloscope to troubleshoot digital busses. Don't skimp on the channel count, go for 4! For things like serial busses (RS-232, SPI, I2C, etc.) you will want to watch clock, tx, and rx simultaneously. For a parallel bus, you can get your clock, chip select, and a couple addy or data lines. For most problems on your board, you can get by with the scope instead of an expensive logic analyzer if the scope has enough channels. The scope is better than the logic analyzer in many ways as you can watch for issues with noise, bus contention, etc.
Every engineer has their bias, I say go for Tek! LabVIEW and DAQ are cool for repetetive measurements under automation, but there's just no substitute for a physical front panel interface with knobs and buttons when you just want to spend a couple minutes looking at a few levels.
Try to find something with Ethernet or USB. Many of the used scopes on ebay have the old 3.5" floppy, and that becomes annoying when noone in the office remembers floppy disks and you need to get a plot off the scope to send to an FAE! :)
What lab will reject an instrument "due to it being fixed"?!
You used a 10% resistor that seems "close enough" the original was 1%. The calibration lab is used to making "minor tweaks" but having to twist all those trimmers practically all the way is going to take forever and piss them off. On the other hand, in Moms Basement, watching a Star Trek movie marathon while calibrating a scope is considered fun, not a waste of time.
You used inductive metal film resistor which screws up the high frequency performance instead of the specified non-inductive carbon comp resistor. It'll never work above 90 MHz again. The calibration lab will throw a fit because it won't calibrate at 100 MHz. However in Moms Basement you are thrilled to own a "90 MHz scope" even if the front panel label claims its a 100 MHz scope, especially since the highest clock frequency you'll likely subject the thing to anyway is probably low double digits.
You used the totally wrong temperature comp capacitors, and trimmed the rest of the scope so it'll work fine at 70 F. Unfortunately the industrial specs say it has to be calibrated from 32 F to 125 F so it simply can't pass calibration. The calibration lab will throw a fit, although it works fine in Mom's temperature controlled Basement.
That's before you start trying to mix old Tektronix scope silver bearing solders with traditional Pb/Sn and with modern lead free. I understand old fashioned Pb/Sn solder will corrode the plating off the Tek silver solder ceramic things.
"Science flies us to the moon. Religion flies us into buildings." - Victor Stenger