Isoloated scope probes

[itsmoked]

thread248-221351

Looking for recommendations on isolated (differential?) scope probes. I'm thinking non-battery powered ones drip with inconvenience so I'm only interested in battery powered ones.

Need up to about 800V I guess.

Any favorites?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Comcokid]

I do a lot of switch mode power an inverter design work. I use the Tektronix P5205 all the time, and sometimes several at a time. Of course these power from the scope so you need a TDS3000 series or a Tek 1103 probe supply to use it with another scope. If you use these with one of the more recent DPO or MSO scopes you need a Tek TPA/BNC probe adapter. This model probe and scope are available eBay for good prices. But, the TPA/BNC adapter are around $500 if you get them used or new. These probes work well either looking at the waveform details of a high-side MOSFET gate at 2V/div, or the 500 V output of a push-pull high-voltage transformer at 100V/div. Tektronix has newer model probes like the TMDP0200 but the price of these new is more than a older model scope and probe cost used.

There are battery powered HV differential probes available. These can be bought from many of the electronics components distributors. They go under a variety of names and branding, but they all must be made by the same source as they're generally yellow and look the same. These use 3 AA batteries or a wall-wart. I made a small regulator module as the Tek 3034B scope has a 15V jack on the backside an a simple linear regulator will allow you to power it where the wall wart plugs in. One caution about these is that when the batteries get weak they tend to oscillate which will drive you crazy trying to figure out what's up with your circuit until you discover it's the probe. The other problem with these is when under battery power you always forget to turn them off, and batteries only last about 30 hours of probe operation.

 

[ScottyUK]

LeCroy's probes aren't bad at all: quite a bit cheaper than Tek, and decent performance.

http://teledynelecroy.com/probes/high-voltage-differential-probes/

Might be worth a look at Keysight (Agilent / HP) too. I haven't used any of the present-day range but the previous generation were pretty good.

 

[sibeen]

What bandwidth and category rating are you looking for as these are going to affect the price.

 

[itsmoked]

Thanks everyone for the input!

I'm having a little fun going over all the offerings. My opinions are slowly shifting because some need USB supplies which some scopes have. I could also use some OTS USB supply battery box for road work.

Thanks Comcokid for the detailed Tek rundown.

I'm a little annoyed at the price of the Tek ones since they probably cost all of about $80 to produce, so them charging $1k is pretty grating on my wallet psyche.

Don't Scotty.. I couldn't find the one I thought would fit and $2k is tooo much.

sibeen; Typical motor/power stuff so not real fast. 50MHz would likely be more than enough for troubleshooting, perhaps not fast enough to do development. CAT 2 would probably work.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

Probes and floating measurements
I have been trying to find a good solution to the problem most of my life. Batteries? No, not really. But if needed, they have to last l-on-g. CMRR? Yes. Need that. High voltage and cat III? Yes, at least 600 V RMS and 100+ A fuses. Sometimes, the Isc is around 10 to 50 kA. Bandwidth? Seldom more than 10 MHz needed.
What do I use?
1. A very old Fluke DP120. With an extra battery pack (6x1.5 V AA) glued to it. 1200 V peak and 20 MHz. Runs for days between battery change. Problem: I only have one and I don’t trust Fuke any more.
2. Scope with more channels and measuring with ground as a reference. Careful probe compensation and A-B on screen. BW is then as good as your probe+scope. If scope is several times probe BW, you can forget the scope. Resulting BW is SQRT(sum of times squared).
3. Battery scope. That seems to be the ideal solution. But CMRR is terrible when you get up to MHz. Can’t be used. Tried several Fluke handheld scopes. Don’t work well when observing VFD outputs. Not even the C&A OX7204 can handle that kind of measurements without problems. OK, better than the yellow ones. But still.
4. USB scope with built-in differential probes. Best solution for the limited budget. I use a PicoScope 4444 with three differential inputs (8x4 mm banana sockets) and one “ordinary” BNC channel. Diff probes go to 10 MHz and BNC to 20. Suits me fine.
5. For high Isc, I use fused (and current limiting) strips that can handle 50 kA at 500 V RMS. That is OK for me.

Now looking at little A/D:s with Bluetooth. Batteries? Yes. But low drain and no CM problems whatsoever. Will probably use those when they start getting as good as I hope for. Maybe they are there already? Any input?


Gunnar Englund

http://www.gke.org

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

 

[Skogsgurra]

Sorry, 6x4 mm, of course.

Gunnar Englund

http://www.gke.org

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

 

[sibeen]

Dave Jones at EEVblog sells a battery powered, Cat 111, 70 MHz diff probe for less than $500.

https://www.eevblog.com/product/hvp70/

 

[Skogsgurra]

Good to know. Tested them?

Gunnar Englund

http://www.gke.org

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

 

[Skogsgurra]

sibeen, I had a look at the diff probe at EEVblog. As always, there is a price for high speed. In this case it is the 100 mA consumption at 6 V DC. That won't last long with AA cells. Hardly overnight when you are looking for intermittent problems. On the other hand, 10 MHz is OK in my applications. But sure good for other purposes.

Gunnar Englund

http://www.gke.org

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

 

[sibeen]

Gunnar, I haven't gotten around to buying one as yet, although I keep promising myself that I'll get around to it. Unfortunately I was bought up in the time where we cut off the earth pin, placed the oscilloscope onto a plastic milk crate and then were very careful about how we changed the vertical and horizontal scales. All without filling out a safe work method statement

 

[Skogsgurra]

Didn't you!!
No gloves either? Or visor? But you sure wore flame-retardant clothing? Like the fluke ads show.

Gunnar Englund

http://www.gke.org

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

 

[waross]

The fun part was getting the super to touch the scope of his own volition when he came poking around the shop.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Comcokid]

If you don't need the 70 MHz bandwidth then here is a lower cost probe 25 MHz for $379 USD.

https://www.picotech.com/accessorie...ential-probes/25-mhz-700-v-differential-probe

This, and the one shown by eevblog is what I mean by a generic name-branded HV differential probe. If you look they are essentially the same - same molding on the soft case, same location for the switches, LED, etc, just different colors and overlay. If you search you will find them from 25MHz to 70MHz, 700V to 1400V, and even 7000V (100:1/1000:1). Someone out there is making them but sells them name-branded through other OEMs.

The generic I happen to have is branded picotech (as above). Works fine but I've mostly gone to used P5025s bought off eBay for a little as $150.

 

[DanEE]

Gunnar, I haven't gotten around to buying one as yet, although I keep promising myself that I'll get around to it. Unfortunately I was bought up in the time where we cut off the earth pin, placed the oscilloscope onto a plastic milk crate and then were very careful about how we changed the vertical and horizontal scales. All without filling out a safe work method statement bigsmile

Brings back memories of when I learned the hard way how to make proper noise measurements with what was available to get a differential measurement.. i.e. using the add and invert function on a two channel scope to get differential, isolated from ground noise measurements of large computer system DC distribution using only probe tips, (ground leads not connected) and 100x probes for higher voltages...

and, doing power supply leakage current measurements on single phase products.. Hot side to ground easy, for neutral side leakage, connected machine ground to hot side of line and then looked for neutral side leakage to "ground". For a lab that was obsessive about safety, it seem strange we were allowed to do this (having large computer product frame ground floated up to 120VAC in this case), but only way to get the numbers needed for certain country leakage limitations. At the time Japan had the most stringent leakage current limitations for agency approval.

 

[Skogsgurra]

Yes! Those were the times.
I worked for Siemens, Germany, then. Im "Prüffeld" (the lab area in Munich) there were some very strict safety rules. Scopes were covered in Lucite/Plexiglass which made operation very impractical. The ground pin was covered with a "Mipolam" tubing to cut ground path. That worked for a while, until the scope (TEK 545A) had been moved around and the Mipolam had worn down a bit. We were testing MW drives and set everything up before the 400 V breaker was switched on. When I did so, I heard a loud bang and saw smoke from the test area. We lost a couple of probes and a lab assistant for a few hours (he was OK, but his underwear wasn't). The Scope was OK. I got ourselves an isolation transformer after that. A Sola with static screen.


Gunnar Englund

http://www.gke.org

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