Reasonably priced differential probes

[Mechatrommer]

True... but the price is hard to beat 

but the performance is awful, its better to slap few opamps and volt divider into a active differential probe diy circuit. the diy circuit will be awful but 2dso probes setup is more awful.

...I would try looking at instrumentation amplifiers first...

pointless! your bottleneck will be in the attenuator (voltage divider) infact thats where the most work will be fought for, unless we have 1KV diff input capable ins-amp off the shelf.

[grantbob]

the OEM is http://www.sapphire.com.tw/

Interesting... the "Important Message" on their web site states:

"Dear customers,
GuangZhou Dekem Electronics Co., Ltd (brand name: Pintech, www.pintech.com.cn) has completely cloned our
products, including the appearances, cable material, nameplate layout. Even their online instruction manuals
( www.pintech.com.cn/uploadfiles/201312103740873 ) are exactly the same as ours."

Makes it even more fut to try to figure out what you're getting.

-grantbob

[Mechatrommer]

the internal construction has become no secret several people have made the teardown, its just a matter of someone with the unit and the balls to make proper documentation about it. the stage of it being within reach of diy is very close. i havent time to get back to the project, there is no black magic in there, if there is, its in the input attenuator front end stage thats where the most mistake made (with some other things perharps)

[Alex Eisenhut]

have you considered old tektronix p series probes? with attenuator.

The P6046 is very difficult to get working properly and to meet its specs, but if you can do it it works well.

Or for the adventurous, a 132 power supply and a 1A5 diff amp plugin with two probes works wonders. You can also connect a p6046 directly to a 1A5.

[dadler]

I have the diff. probe from the link above. In the x20 mode the maximum voltage is 35V. This is definitely in the voltage range you are looking for.

So I received the PINTEK differential probe and it works as expected. As a test (not my primary use case) I was able to decode a CAN stream with differential trigger/decode using the probe. Works well, not too terribly noisy, sorry don't have any exacting description other than "works as expected". I'll try on higher voltage stuff soon.

The build quality is decent. It's better than I thought it would be, the probe box is hefty and solid for the most part. For some reason, they cut the bottom 3/16" of the metallic serial number label off with an X-acto knife. Similar on the power adapter, not sure what they are hiding?

The included power adapter leaves quite a bit to be desired. It's labeled 9V 300mA, but it's unregulated and reads 15v unloaded. It feels super cheap, so maybe a better power supply is in order, or I'll just run it off a 9V battery.

I kinda feel bad that these probes are clones of the Sapphire products, but oh well?

[nctnico]

Perhaps Pintek is the OEM after all

[pascal_sweden]

Note that Pintek also has a low voltage differential probe with high sensitivity.

Pintek DP-30HS:

http://www.pintek.com.tw/files/pintek/DP-30HS-40LV-DM-frond.jpg

http://www.pintek.com.tw/files/pintek/DP-30HS-40LV-DM-back.jpg

http://www.pintek.com.tw/files/pintek/DP-30HS-40LV-MANUAL.pdf

I read that Pintek is cloning Sapphire. Is the quality similar as Sapphire or much worse?

Rigol has differential probes that look very similar as Pintek, but then again it could be an OEM from Sapphire, as Pintek clones Sapphire Does anybody know if the Rigol one is from Pintek or from Sapphire?

I wonder if Sapphire has an "original" DP-30HS variant as well.

[McBryce]

Thanks for the info. After evaluating all the options, I think I'm going to go for the Pintek 40LV.

McBryce.

[dom0]

True... but the price is hard to beat 

but the performance is awful, its better to slap few opamps and volt divider into a active differential probe diy circuit. the diy circuit will be awful but 2dso probes setup is more awful.

...I would try looking at instrumentation amplifiers first...

pointless! your bottleneck will be in the attenuator (voltage divider) infact thats where the most work will be fought for, unless we have 1KV diff input capable ins-amp off the shelf.

There are a few with very high common mode voltage ranges.

- AD629: +-270 Vp common mode, protected to +- 500 Vp common *and* differential mode. 500 kHz BW.
- INA149 is a similar part
- INA148 too
- AD8479: +-600 Vp common mode, +- 900 Vp for 10s AMR. 130 kHz BW.

Of course none of these are isolation amplifiers! But that's okay for lab-use, if you aren't using an isolation/safety transformer to power your DUTs in the lab you're mad anyway.

[nctnico]

An isolation transformer does more harm then good in a small lab which isn't setup to make sure everything is isolated. It is very easy to ground a DUT through test equipment or even a piece of steel from a bench. All in all isolation transformers are a thing of the past. Nowadays use a sensitive GFI and differential probes with the proper safety ratings.

[nowlan]

Is that DP-40LV safe for switching supplies at 650v?
I was interested in the DP25 but price is still to high for a rare use item.

[pascal_sweden]

DP-40LV is actually more expensive than DP-25.

While it has lower voltage range, it has higher bandwidth and better precision.

[Mechatrommer]

There are a few with very high common mode voltage ranges...

yes but they are sub MHz BW, thats a thing of the past. otoh i agree with nctnico thats we seldomly see isolation transformer probe around, or maybe they are highly specialized purpose. when someone asking how to probe mains, everybody adviced go for isolated diff probe, and then go for [insert your fovourite cheap HV diff probe here], didnt they know that [insert your fovourite cheap HV diff probe here] is not isolated? the thing in between is just few big fat arse carbon or ceramic resistors. thats the isolator if ever you want to call it isolated.

[Gromitt]

I read that Pintek is cloning Sapphire. Is the quality similar as Sapphire or much worse?

No. it's not Pintek (Taiwanese company) that is cloning Sapphire, it's Pintech (Chinese company).

[dadler]

I read that Pintek is cloning Sapphire. Is the quality similar as Sapphire or much worse?

No. it's not Pintek (Taiwanese company) that is cloning Sapphire, it's Pintech (Chinese company).

Ahh, I guess I feel better? Hehe. Geez.

I found this comparison chart:

http://www.pintek.com.tw/files/pintek/PROBE-COMPARISON-CHART.pdf

Also, PINTEK claims then DP-25 can operate fine on 5V. I am going to try using USB and see how the probe performs.

[pascal_sweden]

Beginner's question:
If you debug a low voltage circuit on a breadboard (e.g. amplifier circuit with transistor), and you power the circuit with a power supply which has an isolated DC voltage output, then your (-) on the circuit is not ground.

Can you connect the ground clip of the probe on the scope to the (-) anyhow, to actually make the (-) of your circuit become ground?

Or given that the (-) terminal as such does not define an absolute potential level, but only relative to the (+) terminal, could the potential level be high enough to actually cause a short, when connecting the ground clip of the scope?

[Mechatrommer]

Beginner's question:
Can you connect the ground clip of the probe on the scope to the (-) anyhow, to actually make the (-) of your circuit become ground?

yes. for a floating circuit like you described, you can even plug the gnd clip to anywhere in your circuit to make that node gnd. so say you plug the gnd to +ve floating supply, you make that as gnd reference and rendering the rest of the nodes/circuits be measured as -ve voltages. you can also do this with not floating circuit but floating scope, but its dangerous when you connect gnd clip to say 240V, you render every gnded outer metal on the scope as 240V.

[pascal_sweden]

So if you are working on a logic circuit with a MAX232 chip to drive serial line, and you would connect the ground clip of your scope to the 12V point in your circuit, your metal house becomes 12V, which you can start feeling when you touch it? For 5V circuit it is no concern I guess, but the moment voltage becomes 12V or higher, it starts to get "hot".

[Galenbo]

For 5V circuit it is no concern I guess, but the moment voltage becomes 12V or higher, it starts to get "hot".

Since when is 12V considered dangerous?

30V is still safe, and 20 years ago people were stronger, 60V was safe then.

[pascal_sweden]

Suppose you only work on low voltage circuits (e.g. 5V, 12V, 24V), and you use a power supply with isolated outputs.

As indicated above, it is no issue to connect the ground clip of the probe with any point in the circuit, it just makes that potential level your ground from then on. That's clear.
The case of the scope could become 5V, 12V, 24V. Not pleasant to touch, but not harmful.

But I guess it still makes sense to have a differential probe anyhow, as you can still short your scope when you would connect the tip of the probe with the ground clip (not being actual ground, but having a higher potential level).

The differential probe can not be shorted, it only measures the difference between two potential levels. The probe of the scope can be shorted, when clip and tip have different voltage levels and no resistor is in between. Is that correct summary?

I told these observations to a friend with a 4 channel scope. He wondered why the manufacturers of scopes not just build this in as standard. This would make it cheaper as well, when it becomes mass production (a la Rigol). As there is no such scope, he is planning to buy 4 differential probes at once to avoid all the discussions and worries at once. Maybe Pintek offers a discount when buying DP-30HS differential probes in bulk

[dadler]

Explained another way: A good reason to have a diff probe is that even if your circuit is floating, you can have one channel have a different "ground reference" than the other channels. With no diff probe, you are limited to a single ground reference potential and you may not be able to use the other channels on the scope depending on your use case.

[dom0]

There are other reasons to use diff probes and amplifieres, too. Many lab supplies, especially cheaper ones and probably all people build themselves don't have a shield winding in the mains transformer, which means that there is a substantial capacitance (up to a few dozen nF for large toroidal transformers) between mains and the floating supply. This usually makes it undesirable to connect the ground clip to nodes that aren't low impedance.

See attached screen grab for an example. Node impedance is about 250 k?.

[tautech]

Suppose you only work on low voltage circuits (e.g. 5V, 12V, 24V), and you use a power supply with isolated outputs.

As indicated above, it is no issue to connect the ground clip of the probe with any point in the circuit, it just makes that potential level your ground from then on. That's clear.
The case of the scope could become 5V, 12V, 24V. Not pleasant to touch, but not harmful.

But I guess it still makes sense to have a differential probe anyhow, as you can still short your scope when you would connect the tip of the probe with the ground clip (not being actual ground, but having a higher potential level).

The differential probe can not be shorted, it only measures the difference between two potential levels. The probe of the scope can be shorted, when clip and tip have different voltage levels and no resistor is in between. Is that correct summary?

I told these observations to a friend with a 4 channel scope. He wondered why the manufacturers of scopes not just build this in as standard. This would make it cheaper as well, when it becomes mass production (a la Rigol). As there is no such scope, he is planning to buy 4 differential probes at once to avoid all the discussions and worries at once. Maybe Pintek offers a discount when buying DP-30HS differential probes in bulk

The "general" issue of GND loop shorts is addressed by manufacturers with Isolated channel scopes. These are not cheap either, but you're dealing with preserving signal intregrity, not easy at higher BW's.
For those that are examining 3 phase waveforms a lot, this is the best long term solution.

Richard made a nice comment in another thread:
https://www.eevblog.com/forum/testgear/best-practice-for-protecting-a-scope-that's-probing-mains-attached-devices/msg659425/#msg659425

Where the reference lead is attached is the root of all these problems.
For noobs and the inexperienced it is called the GND lead, no doubt to remind us that incorrect connection will introduce a ground loop. But remember it is the "signal reference", first and foremost.
Of course with the use of isolation techniques like Differential probes, Siglent ISFE or isolated channel scopes, risk of damage to the DUT or scope is minimised.

[dom0]

The same circuit powered by a lab supply w/o a shielding winding and stacked windings, so with a transformer that has a large coupling capacitance.

Whoops. A whooping 45 Vpp AC, enough to destroy more sensitive devices.

So this is just another consideration when considering ground clip placement ; high impedance nodes... better not...

[Keylectric]

I told these observations to a friend with a 4 channel scope. He wondered why the manufacturers of scopes not just build this in as standard. This would make it cheaper as well, when it becomes mass production (a la Rigol). As there is no such scope, he is planning to buy 4 differential probes at once to avoid all the discussions and worries at once. Maybe Pintek offers a discount when buying DP-30HS differential probes in bulk

If I get you right you are under the impression that there are no scopes with differential inputs?

If so there are actually, however not that common.

Picoscope for example have a four channel USB-scope with all inputs differential. Limited bandwith but anyway.