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MagicSmoker. LOOK! I got you another post.

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itsmoked

itsmoked

Electrical
Feb 18, 2005
19,114
MagicSmoker said:
I am in 100% agreement with you about the old Tek THS-720P portable oscilloscopes, and I've even called up Tek once or twice to beg them to revive that product line. I still use the THS-710P I purchased brand new in 1997, despite also now owning its theoretically superior replacement, an AEMC/Metrix OX7104-III (but that is a tale for another post...)
Click to expand...

I'm still looking for something to replace my THS720. I can't believe how Tektronix has fastidiously ignored this important area for the last 15 years.

For those of you who don't know the THS7xx series are a battery power-able handheld scope that's isolated between channels and between channels and the wallwart. It's a gem for scoping triggering circuits and the isolated power outputs. Triac, heaters, PWM, all those types.

Keith Cress
kcress -
 
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Hi Magic (and Smoked)!

I use the Metrix OX7204, too. That is the best performing portable four-channel scope I have had under my nails. The THS 720, I liked a lot. But it didn't have much software for the PC end.

But, mind you, even if those portable all-port isolated battery scopes can be used without problems almost everywhere, you still cannot measure across two motor terminals on a PWM driven motor. There, you either need an insulation amplifier or need to do N-A, N-B and N-C measurement and then do the A-B, B-C and C-A math in the scope. The 7204 can do that. There are well-known brands that aren't able to do that. So, I guess that the 7204 still is the winner in that league.

I haven't tried the available SW downloads yet. But I will do that one day when I feel lucky.




Gunnar Englund
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Half full - Half empty? I don't mind. It's what in it that counts.
 
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Yeah, the THS scopes were excellent in their day. The Tek TPS series had so much potential but it was a full generation behind their mains-powered range and it was especially limited in its ability to catch fast non-repetitive events so I never took the plunge. If it got brought up to date then maybe I would.

I'd like to have a play with Metrix type, just to see if it's as good as Gunnar says.

 
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Careful, Scotty!

I was just as excited as you. Then I read the specs.

No more than 15 waveform memories - although they can store four traces each. But still no more than 15 separate measurements. The rest (also limited) needs to be stored as bitmaps. I must ask myself, again: WHY on Earth economize on something as important as storage space? An SD card would have solved that problem.

The math I described above can't be performed. Not possible to use more than +, - and x and only one result channel. I usually need three to make Three-phase measurements.

Accuracy! Have a look at the specs:
Vertical accuracy
5 mV/div to 100 V/div ±(2.1% + 0.04 range/div)
2 mV/div ±(2.9% + 0.08 range/div)
At 1V/div you get +/-(21 mV + 40 mV) = +/-61 mV, which corresponds to around 6% error margin. I need better. Doesn't matter if you go to 100 V/div - same error margin. I wonder if this is a mistake. It can't be that bad.

But, perhaps it can. The automatic measurements are shown with 999 maximum Count. That is not impressive. A tru 3 digit display - not even a "3.5" digit display.

AC accuracy (results shown on the 999 display is:
AC coupled, high frequencies
60 Hz to 20 kHz ±(2.5 % + 15 counts)
20 kHz to 1 MHz ±(5 % + 20 counts)
1 MHz to 25 MHz ±(10 % + 20 counts)
So, if you need to measure a 1 V 1 MHz sine, you can't trust the result to be better than +/-(1V*10% + 20) = +/-120 mV or +/-12%. Again, I must ask myself if there is a mistake in the specs.


Vertical resolution isn't good either. Just 200 pixels. The screen is 320x240 pixels.

I was, as I said, also in need of one of these. But I cooled off quite a bit after reading through the data sheets and the manual. I don't even think that a super low price tag could lure me into buying one. Sorry. We do need better than that. I expect the Chinese to bring a decent and easily affordable scope on the market. In the meantime, my "French mistress" works well for me.



Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
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WOOT!!

Have to take back any denigrations just made..

Nice find Scotty. <drool>

Looks like Gunnar's Metrix but less $$ and not noxious blue. :)

Keith Cress
kcress -
 
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What does a ths 720a go for these days. I have one that I put on the shelf after getting my Rigol.

 
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Check ebay, but I can see them in the 1000 GBP range and upward. Not bad for a 20-year-old instrument.
 
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!! Gunnar's post was not there when I last posted.. Thanks for the spec run-down Gunnar. I agree it does look less inviting with those issues.

Keith Cress
kcress -
 
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Yes, same meager memory set-up as the Fluke thing that I expected to be better. And the math isn't there either. At least not the math I need.

I may have been a little harsh on the screen resolution. But I think that the screen shots are rather ragged.

There is definitely more resolution and better accuracy with the AEMC/Metrix scope's 12 bit A/D instead of the THS and Fluke 8 bit A/D.

No touch screen, as far as I can see, on the THS 3000. And that makes many operations quite complicated. Like zooming and setting cursors and other common tasks.

What is the price of the THS3000? Can't find it.

Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
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Sorry, I saw the "Get a quote" box and assumed that there wasn't any price information. But it's all there if I had scrolled down a bit.

OK, those prices are not dramatically lower than what a French mistress costs.

Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
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Yeah, I'd have to agree there. They're all pretty steeply priced. Probably too rich for me. I do all sorts of things so not a great enough focus on industrial waveform issues to justify the hit. You with your paper-mill and motor/VFD focuses are certainly more justified in keeping a French Mistress.


Hope your spouse isn't reading this. :)

Keith Cress
kcress -
 
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Haha, Keith.

She knows about my somewhat kinky relation to the OX7204. She even gave it a French name: Cri-cri!

Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
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I happen to know (or rather have met) someone named Cricket Batz - just sayin'...

Gunnar Englund
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Half full - Half empty? I don't mind. It's what in it that counts.
 
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