Computing stuff tied to the physical world

Instrument limits

In Hardware on May 3, 2013 at 00:01

Last week’s post illustrated some limitations of electronic measuring equipment. In this case, I was using the TTi TG2511 Arbitrary Waveform Generator (which I have yet to use for “arbitrary” waveforms) and the Hameg HMO2024 Digital Storage Oscilloscope.

The TG2511′s rise and fall times are specified in the neighbourhood of 10 ns, which has a fairly atrocious effect on a 25 MHz “square wave” signal:

SCR01

(the scope’s own rise time is under 2 ns)

Both are excellent instruments, but already fairly high-end for hobbyist use. To put it in perspective: the total cost of this sort of equipment is more than a hundred JeeNodes with sensors! Add to that the fact that you only need the higher specs of these instruments once in a while (how often depends of course on your level and depth of interest), and it’s pretty obvious that it can be very hard to justify such expenses.

I’ve always been annoyed by this. And I’ve always been on the lookout for alternatives:

DSC_4438

DSC_2780.jpg

That’s the Xminilab, mentioned recently, and a sine-wave generator from eBay. The total cost for both is around €100.

Unfortunately, lower-end equipment really does have lower-end specifications. The measurements made yesterday could not have been done with the above, for example: sine waves are not square waves, and the 2 megasamples/second of the Xminilab scope is not fast enough to analyse rise times at 1 MHz, let alone 10 MHz.

Tomorrow, I’ll explore (“review” is too big a word for it) a more affordable modern oscilloscope, to show what can and cannot be done with it.

  1. Unfortunately you are right it is hard to justify the cost of good lab gear for private use. On the other hand it is so much more fun to work with (semi) professional gear. And there are always new cool features to discover instead of bouncing against limitations. So for myself I made a rule to buy good gear only I find a bargain.F.e. Scopes are notorious for great discounts, last week there was a 25% discount for Agilent scopes at Farnell.

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