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Forum Index : Electronics : Looking for an oscilloscope
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Haxby Guru  Joined: 07/07/2008 Location: AustraliaPosts: 418 |
Hi all, Looking for a well priced oscilloscope.  This one has been mentioned on this forum. Any other ideas? I'd prefer getting one locally as I don't want to put my project on hold for 3 months waiting for it to arrive. The one above is available in Brisbane for $400, which is ok I guess. Any other suggestions? |
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renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
This is the one I got, haven't used it hardly, but it has plenty of features and not pricey. Cheers Caveman Mark Off grid eastern Melb |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
That looks like an excellent buy Mark. Cheers, Tony. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
I think I paid less than that for it almost a year ago, been so busy with other things I haven't used it properly yet. NO, I just checked, I paid $319 for it. those sons of bitch f'ers dropped the price. Edited 2021-01-16 17:51 by renewableMark Cheers Caveman Mark Off grid eastern Melb |
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| Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 418 |
Ok I bought it. Thanks all. |
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| Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 418 |
What's the the best way to look at a high voltage transient trace without blowing up the scope? |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Not having it grounded to mains earth for a start. Use the probe on high scale. Also look here BTW the scope I got had a US plug with a Aus adaptor which only had active and neutral on the adaptor, so if that's what you get job done, use as is, but be aware not to stick it somewhere you shouldn't as you are not earth/safety switch protected. Edited 2021-01-16 18:42 by renewableMark Cheers Caveman Mark Off grid eastern Melb |
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| Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 418 |
It could be up to a 1kv transient. The scope is probably only good for 400v. Is a X10 probe really enough? I can easily float the device under test. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
 Or maybe probe through a transformer? Dunno, ask Warp, he'll know. Cheers Caveman Mark Off grid eastern Melb |
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poida Guru Joined: 02/02/2017 Location: AustraliaPosts: 1388 |
Using the DSO you just bought: All BNC connectors have their outside conductor connected to mains supply earth. So that means channel 1 earth lead = channel 2 earth lead = external trigger earth lead = ground = Earth from mains plug = Neutral from mains plug. Looking at "high voltage transient"... Ok, first I ask what is this voltage to be referenced to? Is it high voltage relative to ground, the ground that will be connected to mains Earth, and, this one got me a month ago, it will also be connected to all USB grounds, and any ground you choose to connect things to via USB. and other things. Let's say the high voltage transient is a voltage present that makes sense to measure with the ground lead on the ground plane/pin of the device under test (DUT) and this ground = mains Earth = everything else ground Now we need to look at what is the maximum voltage the DSO inputs can take: The manual sez for the Hantek DSO5102P: 300 V RMS applied to the 10x probes, 150V with 1x probe or directly input into BNC terminal. excursion above 300V must be less than 100ms If high voltage is 1KV, then you will need to use some sort of voltage divider, then probe the reduced voltage. But maybe the high voltage transient is referenced to something that is NOT ground. It could be mains voltage. OR Battery DC positive. OR the output of a flyback converter or something. Now the earth lead of the DSO really should not be connected to what maybe called "signal ground" or else that is now mains 240V or battery DC+ or whatever. Ahh, I will use a HV differential isolated probe, you think. For a start, there are no cheap HV differential probes. But I highly recommend them. You get HV attenuation, differential input and it's isolated from ground. With one of these you are good to probe just about anything and do it safely, not killing yourself, your DSO or other gear on the same ground. (such as the powered USB hub I blew a month ago.) I use the Pintek DP-25 diff probe. 1 channel, 20x 50x and 200x attenuation. 600V RMS isolation for both + and - inputs to output ground. Also I use and like more and more the Tektronix A6902B Isolator. You get 2 channels, not just one in the case of the Pintek. 3000V isolation. Big and safe isolation of the input + and ground leads of both channels, and a wide range of attenuation ratios. You need to find one on ebay in the US and import it. The Tek A9602B does not perform quite as well as the far more modern Pintek and there is a quite bit more noise in the signal but you get 2 channels. With the A6902B you can connect channel 1 ground to something up to 3000V and still see a signal riding on top of that 3000V, AND connect channel 2 to some other HV signal with it's ground lead on some other nasty HV potential. And not blow up stuff. wronger than a phone book full of wrong phone numbers |
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| Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 418 |
I should have given more info: I'm specifically looking at scoping the IGBTs in the high voltage warpverter I'm building. There is no problem in floating the whole inverter with an isolation transformer. The power supply is up to 400v, and the hunch is that the transients are blowing the IGBTs so maybe over 700V, or 1kV or more. If I just used a resistor divider, would that be sufficient? I'm thinking yes, but just don't want to blow up the scope. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
The x1/x10 probe you get with the cro will be adequate for almost anything you do. For looking at really hairy stuff, I made myself a home brew x100 probe. Usually in those circumstances extreme accuracy or extended frequency response is not as important as being able to see "something". If the 800v spikes I am seeing are really only 770v or 815v I really do not care. Just knowing they are there at all, is usually quite sufficient. I use that probe about once every two or three years, but it is useful sometimes. Edited 2021-01-17 08:01 by Warpspeed Cheers, Tony. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Just found this on flea bay: https://www.ebay.com.au/itm/Hantek-T3100-X100-2500V-100MHz-High-Voltage-Probes/293157460339?epid=2227774279&hash=item44418bd973:g:KWoAAOSwLghZsL5A Cheers, Tony. |
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| Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 418 |
Ok I'll try floating the inverter and using a 10:1 resistor divider before the X10 scope lead. |
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Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 583 |
I assume you know that resistors have a voltage rating so don't use the little 0.25W ones  .I found that the aerosharp transformer makes a good isolated mains supply (good for 3 KW), if you can unwind a few turns from the 250v winding you get a 1:1 ratio. I did not bother and use a Variac on the input side. My old fashioned analog CRO has a switch on the back that disconnects the earth from the mains cable. What poida said above is a little misleading, the neutral connector is *only* connected to earth at the mains switch board. So, using a two wire mains cable is the same as having that little switch my CRO has. Of course, these voltages can kill you easily, even at the far side of the isolation transformer. But touching only ONE power wire when there is an isolation transformer is the same than a bird feels sitting on one of the power lines. |
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| Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 418 |
Thanks warp, I bought it.  |
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| Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 418 |
Might get one of those isolated battery operated probes too. Then I can scope both high side and low side IGBTs. Low side through 100x non isolated probe, and high side through isolated probe. That should give me the full picture. |
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| Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 418 |
Thoughts on this one? probe |
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| poida Guru Joined: 02/02/2017 Location: AustraliaPosts: 1388 |
That one looks fine to me. I use this diff probe and it's more expensive but I can not see any reason to buy it now when the DP10013 is 1/2 the price. Once you get an isolated diff probe, you can then start looking at gate drive voltages and currents on the high side of a bridge. A 10x probe on the low side gate and DC ground will give you low side gate voltage. And then with the 2 you will see if there is any chance of shoot-through, observe the dead time, observe the classic RC behaviour of the gate and lots more. a very good review of the DP10013 Edited 2021-01-18 09:29 by poida wronger than a phone book full of wrong phone numbers |
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| Haxby Guru Joined: 07/07/2008 Location: AustraliaPosts: 418 |
Ok I got the DP10013 from AliExpress, apparently shipping from Australia so I won't have to wait too long. |
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