Author Topic: Looking for portable oscilloscope  (Read 10001 times)

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Offline abgx1Topic starter

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Looking for portable oscilloscope
« on: December 09, 2023, 01:36:15 pm »
I am about to buy my first oscilloscope.

It will be used for measuring on frequency inverters (mains 400V voltages up to 16kHz), mains voltages in general, and industry sensors. Additionally, I may use it for car electronics.

Measurements will usually be done on-site, in not-so-easily accessible places (like industry water wells in the middle of nowhere).

After some research, I've narrowed it down to 2 options:

1. Rigol DHO804 https://www.conrad.com/en/p/rigol-dho804-digital-70-mhz-1-25-gs-s-25-mp-12-bit-1-pc-s-2986311.html - not very portable, but can be powered from a USB-C power bank.

2. Voltcraft DSO-2072H https://www.conrad.com/en/p/voltcraft-dso-2072h-handheld-oscilloscope-70-mhz-2-channel-250-msa-s-8-kp-8-bit-handheld-1-pc-s-2380256.html - handheld, with its own batteries.

I'm also considering these probes https://www.conrad.com/en/p/testec-tt-hv-250-probe-300-mhz-100-1-2500-v-107255.html for both of them.

Currently, I use a multimeter for these kinds of jobs, but I feel like I could find problems faster if I could see the actual waveforms.

Do you think it's worth trading portability for a 'better' scope (Rigol), or should I be fine with the Voltcraft?"
 

Online Aldo22

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Re: Looking for portable oscilloscope
« Reply #1 on: December 09, 2023, 01:51:11 pm »
I can't tell you what you need, but I can tell you that these devices are available for less.
The Voltcraft DSO-2072H is an Owon HDS272
https://eleshop.de/messtechnik/oszilloskope/alle-oszilloskope/owon-hds272-handheld-oscilloscope.html

And the Rigol is also available at a lower price:
https://www.batronix.com/versand/oszilloskope/Rigol-DHO804.html
 

Offline alm

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Re: Looking for portable oscilloscope
« Reply #2 on: December 09, 2023, 03:08:55 pm »
I'm not familiar with the current products on the market, but I'd definitely look for a scope that can take floating measurements at mains voltages correctly. This means if it has multiple inputs, the reference lead of all inputs should be isolated from each other, the unit should use insulated BNC jacks, and you should use probes made for floating measurements like Stäubli ISOPROBE. Both probe and scope should be rated for CAT III 600V or higher. Note that if the reference lead is at 400V, this is not attenuated by the probe, so the scope would see the whole 400V relative to ground (while the operator holding it might be grounded).

Offline abgx1Topic starter

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Re: Looking for portable oscilloscope
« Reply #3 on: December 09, 2023, 03:41:13 pm »
Thanks, I know I can buy them cheaper. I'm not going to order them from Conrad; it was just the first English website I found.

Oh, I see the hassle. But that's a problem only if I measure across two phases, right?

Can I avoid all the problems you mentioned if I measure only between a phase and ground?
 

Offline alm

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Re: Looking for portable oscilloscope
« Reply #4 on: December 09, 2023, 05:57:20 pm »
With normal probes and non-insulated BNC jacks, the problem is protection against accidentally touching the reference lead (notice how I don't call it ground clip) to phase, and then touching the ring around the probe or the BNC connector, will shock you. In a mains-operated scope this is no problem because the reference lead is tied to ground, so connecting it tho phase will trip a GFCI / breaker or at least produce a spark and probably vaporize the ground lead. With a battery-powered scope you have no such protection. That's why you see the reference lead on the IsoProbe I showed is much more insulated than that of normal probes designed for grounded scopes.

For a single channel, you want an insulated BNC connector on the scope and a scope that has all exposed metal (like USB connectors) and controls sufficiently isolated from the input connector. For a dual channel scope, you ideally also want the two channels to be isolated from each other, not just from the scope, so that if you clip the reference lead of channel 1 to phase, the reference lead of channel 2 won't be live.

Offline abgx1Topic starter

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Re: Looking for portable oscilloscope
« Reply #5 on: December 09, 2023, 09:20:52 pm »
Thats why I want to buy these 100:1 probes.

https://www.conrad.com/en/p/testec-tt-hv-250-probe-300-mhz-100-1-2500-v-107255.html

So even if I accidentally touch them, there will be 2,3V instead of 230V...


Is that a bad idea?
 

Offline alm

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Re: Looking for portable oscilloscope
« Reply #6 on: December 09, 2023, 09:46:58 pm »
Thats why I want to buy these 100:1 probes.

https://www.conrad.com/en/p/testec-tt-hv-250-probe-300-mhz-100-1-2500-v-107255.html

So even if I accidentally touch them, there will be 2,3V instead of 230V..
Only if you connect the tip to phase and then touch the center pin of the BNC connector. But if you connect the reference ('ground') lead to phase and touch for example the ring close to the probe tip, or anything on the scope that is connected to this reference lead (like any connector on a non-isolated scope), there will be 230V on that. The 1:100 attenuation is only for the tip. The same applies to true isolated probes like the one I showed, but those probes are designed in a way that when used with scopes with isolated inputs, the reference lead is well insulated from the user.

I'd say probes like this are not safe for battery powered scopes. Only probes where both the tip and reference lead are fully insulated from the user are safe for making measurements beyond separated extra low voltage (< 50V RMS from a source isolated from mains). Note the note in the probe datasheet (emphasis as in datasheet):
Quote
Never dismantle the probe while it is combined with the voltage source and only connect it to a grounded oscilloscope.
« Last Edit: December 09, 2023, 09:51:48 pm by alm »
 

Offline Fungus

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Re: Looking for portable oscilloscope
« Reply #7 on: December 09, 2023, 10:15:25 pm »
Is that a bad idea?

Possibly.

Imagine you connect the ground clip of a probe to the live phase wire.

All the exposed BNC connectors on the scope are now live...

A 100x probe is a good idea but it's not a guarantee.

Edit: FWIW the DHO800 comes with little rubber caps so you can do this:

« Last Edit: December 09, 2023, 10:19:35 pm by Fungus »
 

Offline csuhi17

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Re: Looking for portable oscilloscope
« Reply #8 on: December 09, 2023, 11:53:32 pm »
Quote from: Fungus link=topic=404805.msg5213088#msg5213088 .
date=1702160125
Edit: FWIW the DHO800 comes with little rubber caps so you can do this:

the "ground" point of the calibration signal is connected to the reference "ground" point of the four channels.
It would also be worthwhile to put a cap on it.
Fnirsi oscilloscope = waste&regret
 

Offline smaultre

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Re: Looking for portable oscilloscope
« Reply #9 on: December 10, 2023, 06:49:13 am »
You can see Fluke 199 series or Agilent U1620.. Isolated inputs are not low-cost thing.
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Online tggzzz

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Re: Looking for portable oscilloscope
« Reply #10 on: December 10, 2023, 09:00:02 am »
I am about to buy my first oscilloscope.

It will be used for measuring on frequency inverters (mains 400V voltages up to 16kHz), mains voltages in general, and industry sensors. Additionally, I may use it for car electronics.

Measurements will usually be done on-site, in not-so-easily accessible places (like industry water wells in the middle of nowhere).

After some research, I've narrowed it down to 2 options:

1. Rigol DHO804 https://www.conrad.com/en/p/rigol-dho804-digital-70-mhz-1-25-gs-s-25-mp-12-bit-1-pc-s-2986311.html - not very portable, but can be powered from a USB-C power bank.

2. Voltcraft DSO-2072H https://www.conrad.com/en/p/voltcraft-dso-2072h-handheld-oscilloscope-70-mhz-2-channel-250-msa-s-8-kp-8-bit-handheld-1-pc-s-2380256.html - handheld, with its own batteries.

I'm also considering these probes https://www.conrad.com/en/p/testec-tt-hv-250-probe-300-mhz-100-1-2500-v-107255.html for both of them.

Currently, I use a multimeter for these kinds of jobs, but I feel like I could find problems faster if I could see the actual waveforms.

You would benefit from reading and understanding the Tektronix references at https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/  especially the safety references.

TL;DR is never float a scope. There are many subtle ways it could damage the UUT, and/or the scope, and/or you.

A few scopes are explicitly designed to be used (relatively) safely in cases such as you describe, typically with isolated inputs.

Make sure any probe's AC voltage-vs-frequency rating is not exceeded. If the probe doesn't have that specified, don't use it.
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline Fungus

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Re: Looking for portable oscilloscope
« Reply #11 on: December 10, 2023, 10:55:56 am »
To be honest: For looking at basic 16kHz signals in outdoor conditions I'd be tempted to go for a single channel handheld. You don't need deep memory, serial decoders, video triggers, etc. for that.

Something like that Voltcraft/Owon shown in the first video would do it. Look for one that can be charged with a USB powerbank.

Maybe even this combined with a decent probe and a voltstick to check which is the live wire and which is neutral/GND:


« Last Edit: December 10, 2023, 11:00:31 am by Fungus »
 

Offline adam4521

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Re: Looking for portable oscilloscope
« Reply #12 on: December 10, 2023, 11:37:59 am »
Middle of nowhere, wells, water, 400V, inverter, it’s like a cacophony of jangling alarm bells. In most contexts this would be super-regulated industrial work. They’d start with whether you need to do the test in situ at all, then would follow detailed risk assessment, method statement, two people at least etc. Eventually, a comparatively low price/performance, but very regulated, isolated, tested device from premium supplier like Fluke might be suitable for the test activity, within a procedure that is entirely written out in advance. Dave has done videos on why those types of device exist and are expensive compared to the hobbyist devices.
 
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Offline alm

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Re: Looking for portable oscilloscope
« Reply #13 on: December 10, 2023, 11:47:02 am »
I'd definitely look for a CAT III rated device designed for floating measurements with properly isolated or insulated (for single channel) connections, and not like the Voltcraft in the first post: "please don't touch the connectors while the scope is connected to a voltage source".

Offline abgx1Topic starter

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Re: Looking for portable oscilloscope
« Reply #14 on: December 10, 2023, 12:29:58 pm »
It's getting way more complicated and expensive than I thought.

I think that intentional floating measurement is out of the game for now. If I understand correctly, the only problem I need to solve now is when I accidentally connect the ground to the mains voltage (which can easily happen).

Now I see that I need to gain a lot more knowledge about scopes. I've read some articles and watched some videos, etc. [Here's a link].

But, what if I buy a scope operated from main voltage? In that case, the ground point will always be connected to the ground in the outlet. So, the worst-case scenario is a short circuit between the scope ground and mains voltage, which is not ideal but much safer than the risk of being electrocuted.

Or should I abandon the idea of buying a scope completely until I'm ready to pay 3-4k€ for the Fluke?
 

Offline csuhi17

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Re: Looking for portable oscilloscope
« Reply #15 on: December 10, 2023, 01:03:12 pm »
Wouldn't any oscilloscope and differential probe solve his problem?
Fnirsi oscilloscope = waste&regret
 

Offline Fungus

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Re: Looking for portable oscilloscope
« Reply #16 on: December 10, 2023, 01:41:15 pm »
But, what if I buy a scope operated from main voltage? In that case, the ground point will always be connected to the ground in the outlet. So, the worst-case scenario is a short circuit between the scope ground and mains voltage, which is not ideal but much safer than the risk of being electrocuted.

Any 'scope can be grounded. The Rigol DHO800 has a grounding connector and comes with a big green/yellow wire in the box.

Me? I say "safety" is as much about procedure as the hardware. You can kill yourself just as dead with a $4000 Fluke as with a cheapo Chinese meter.

a) Wear gloves (and eye/hearing protection for very high power circuits)

b) Don't trust your life to the color of wires. Make sure you know which is the live wire and whether the neutral wire is grounded or not. You need a low-Z multimeter for this. I'd get a Fluke 113 if my job was based around "mains AC" (for it's price, high CAT rating and sheer idiot-proofness).

c) Don't do it alone, have somebody else around whenever possible.

d) ...now you're ready to start the test procedure.

Middle of nowhere, wells, water, 400V, inverter, it’s like a cacophony of jangling alarm bells.

It sorta depends on the power of the inverter. A properly-fused 5A inverter isn't as scary as a 1kA inverter...

 

Offline abgx1Topic starter

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Re: Looking for portable oscilloscope
« Reply #17 on: December 11, 2023, 04:33:55 pm »
Well, at some point, the amperage of the fuse doesn't matter anymore because it just won't trip, no matter how hard you're trying. 🙂 The frequency inverters I commonly come across are in the range of 0.18-11 kW, which means around 25-26A at max.

Anyway, I did some studying, and I see four options:

1. Buying differential probes - That's too expensive, at least for now.
2. Buying a scope with isolated inputs - That's even more expensive.
3. Using a grounding connector with a big green/yellow wire connected to the 100% safe grounding point (for example, a lightning rod on those wells) as a reference point so I do not have to use the probe grounding lead at all - That sounds pretty safe to me.
4. Could I use the second channel as a reference point? I mean, I would connect channel 1 through a 1:100 probe on mains voltage. Then I would connect channel 2 through a 1:100 probe to the ground. Finally, I would subtract channel 2 from channel 1.

Now, when I see it written, I think that option 4 is impossible since I will not be able to measure any voltage on channel 1 without grounding. Is that true?


Currently, I am leaning toward the Rigol DHO804 and option (if option 4 is not possible), if you guys do not have a better idea that does not cost a four-figure price. I have excluded Owon  from selection since it doesn't have a grounding point other than one on the probe..
 

Offline Fungus

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Re: Looking for portable oscilloscope
« Reply #18 on: December 11, 2023, 04:39:02 pm »
4. Could I use the second channel as a reference point? I mean, I would connect channel 1 through a 1:100 probe on mains voltage. Then I would connect channel 2 through a 1:100 probe to the ground. Finally, I would subtract channel 2 from channel 1.

Now, when I see it written, I think that option 4 is impossible since I will not be able to measure any voltage on channel 1 without grounding. Is that true?

Currently, I am leaning toward the Rigol DHO804 and option (if option 4 is not possible), if you guys do not have a better idea that does not cost a four-figure price. I have excluded Owon  from selection since it doesn't have a grounding point other than one on the probe..

No need.

The DHO800 comes with a big yellow/green ground wire in the box. You can ground the scope then just probe the mains with a single probe on channel 1.
 

Offline shapirus

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Re: Looking for portable oscilloscope
« Reply #19 on: December 11, 2023, 04:41:37 pm »
4. Could I use the second channel as a reference point? I mean, I would connect channel 1 through a 1:100 probe on mains voltage. Then I would connect channel 2 through a 1:100 probe to the ground. Finally, I would subtract channel 2 from channel 1.

Now, when I see it written, I think that option 4 is impossible since I will not be able to measure any voltage on channel 1 without grounding. Is that true?
If we consider it from the purely mathematical point of view, since one channel's value is subtracted from another, and they both have the same reference point, the referent point cancels out and does not matter anymore, meaning the probe ground clips aren't even required in this case.
Practical implementation is a different story. I can't confirm that it works, but something tells me that it should be viable.

p.s. you can still touch the exposed ground metal parts on the probes, if they have them. That requires extra care.
 

Offline csuhi17

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Re: Looking for portable oscilloscope
« Reply #20 on: December 11, 2023, 06:26:13 pm »
Well, at some point, the amperage of the fuse doesn't matter anymore because it just won't trip, no matter how hard you're trying. 🙂 The frequency inverters I commonly come across are in the range of 0.18-11 kW, which means around 25-26A at max.

Anyway, I did some studying, and I see four options:

1. Buying differential probes - That's too expensive, at least for now.
2. Buying a scope with isolated inputs - That's even more expensive.
3. Using a grounding connector with a big green/yellow wire connected to the 100% safe grounding point (for example, a lightning rod on those wells) as a reference point so I do not have to use the probe grounding lead at all - That sounds pretty safe to me.
4. Could I use the second channel as a reference point? I mean, I would connect channel 1 through a 1:100 probe on mains voltage. Then I would connect channel 2 through a 1:100 probe to the ground. Finally, I would subtract channel 2 from channel 1.

Now, when I see it written, I think that option 4 is impossible since I will not be able to measure any voltage on channel 1 without grounding. Is that true?


Currently, I am leaning toward the Rigol DHO804 and option (if option 4 is not possible), if you guys do not have a better idea that does not cost a four-figure price. I have excluded Owon  from selection since it doesn't have a grounding point other than one on the probe..

If I wrote something wrong or ambiguous, please correct me, unfortunately English is not my first language.

If it is enough for you to just see the signal and not perform any serious measurements on it, and the display size is fine for you:
Differential measuring head:
Hantek HT8050 for about 180 Euros or Micsig for about 250 EurosBangood sell it cheaper 150USD.
Small handheld scope
HDS242 around 140 Euros.
The 40Mhz configuration comes out to around 320 Euros.
You wrote that ~16 kHz should be around.

If you need a more serious one, the oscilloscope is at least the Rigol DHO804 or maybe the others can recommend a cheap portable version.
Forget Fnirsi and company.
Maybe the DPOX180H, but only if you can get it cheap.
it is worth putting a cap on each channel, and covering the measuring points of the 1kHz test signal with some sort of insulator.

If I understand correctly what you wrote in point 4.
You will not be able to use the two channels in such a way that the "Ground" wire of both channels is not connected anywhere. and You connect the "signal" wire of the first channel to the main voltage and the "signal" wire of the second channel to ground.
This is wrong in principle, since the "Ground" reference point of both channels is "floating?"
Did you read about the differential probe when you came up with this?


Do any of fluke's handheld oscilloscopes have a separate ground?!
Even the Fluke 190 Series III ScopeMeter doesn't include it, that is, I can't see it anywhere, even though it's a +4000 Euro instrument.
As written above, compliance with the safety regulations is the most important.
« Last Edit: December 12, 2023, 10:52:35 pm by csuhi17 »
Fnirsi oscilloscope = waste&regret
 

Offline abgx1Topic starter

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Re: Looking for portable oscilloscope
« Reply #21 on: December 11, 2023, 08:32:13 pm »
cushi, you understand point 4 correctly.

I wasn't reading about a differential probe, it was just a random idea that I got. But now I understand that it is not possible to measure completely without ground when not using differential probe.


So I will stick with option 3 + Rigol 804 and maybe later I will buy some differential probe...

 

Offline csuhi17

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Re: Looking for portable oscilloscope
« Reply #22 on: December 11, 2023, 09:01:00 pm »
ok
When I measure higher voltages, I always use one of the battery scopes, floating.

I don't know how to measure with a grounded oscilloscope!
check properly how to do it, so that there is no problem.
Fnirsi oscilloscope = waste&regret
 

Offline shapirus

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Re: Looking for portable oscilloscope
« Reply #23 on: December 11, 2023, 09:09:20 pm »
Practical implementation is a different story. I can't confirm that it works, but something tells me that it should be viable.
So it doesn't work. I have just verified this with a handheld battery-powered scope: when the ground clips are detached, the Ch1-Ch2 (math) waveform becomes garbage.
 
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Offline smaultre

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Re: Looking for portable oscilloscope
« Reply #24 on: December 12, 2023, 08:59:42 am »
I'm just trying the same trick ch.A - ch.B  with Fluke. I't works fine, math is GREEN line.
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