Reasonably priced differential probes

[pascal_sweden]

I know these scopes exist, but my friend really likes his current 4-channel scope and does not want to change it.

I think that the decision about the need for a differential probe is already made

Now the question that remains is whether it should be a Pintek DP-30HS or DP-40L.

Given that the voltage range is smaller for DP-30HS I would expect better sensitivity and accuracy, but according to the specs it actually isn't. The DP-40L seems to beat the DP-30HS in both BW and voltage range. Or do I miss something? Note that they cost the same!

[akis]

Still...the absolutely cheapest $0 solution is to use the tips of two probes, just inverting one of the channels, voilá 

Aside from the sensitivity issues mentioned above, that only works if you have perfect gain and timing match between the two channels.

Using the two probes method to measure voltage across a small current sensing resistor (my main use for differential measurements) is nowhere near as clean as using an instrumentation amplifier or equivalent opamp when possible.

The most immediate and best way is this: If your scope is battery powered (like mine is) you can unplug it from the mains, and then use the probe + ground clip over the sense resistor or any other parts of the circuit you wish to measure. The "ground" clip of your scope is floating with respect to *anything* you will be trying to measure, therefore your probe is now differential by definition. This is immediate and 0 cost.

Other people simply disconnect the earth from their mains pwoered scopes to achieve the same "floating" probe status, however this is dangerous because there may still be an internal path to the mains supply and then you can burn something or die.

Trying to use the two probes is problematic not only in terms of offset voltages and sensitivity, but also of ability to read values off the screen easily and quickly - I have to use the Maths function which produces a third curve (the A-B or A + (-B)) but I then have to look really closely on the screen to take measurements on this third curve on the screen. Not convenient.

Has noone thought of making a simple (?) circuit to convert a single probe to a differential probe? I am sure we can make a simple circuit to cover low voltages and low frequencies without much trouble.

[pascal_sweden]

Good point!

As the current market situation looks like, differential probes are only built for and in the budget of professionals.

This is actually a bit of a contradiction, because beginners and hobbyists are the one that tend to make mistakes in connections, even when it only concerns low voltages and low frequencies.

From that perspective, the suppliers should think about a beginner/hobbyist differential probe built for and in the budget of beginners/hobbyist.

Here we just have found ourselves a gap in the market and potential business opportunity.
Anybody up for the challenge? Beginnerprobe (R) or MyFirstProbe from TestSkool

[dadler]

Do you consider the above discussed Pintek DP-25 ("economic model") too expensive? It seems reasonably priced for what it is.

http://www.pintek.com.tw/product_detail/landersound/index.php?Product_SN=19265&Company_SN=6002&Product_Site_Classify_SN=17072

I bet someone could reverse engineer it though, and sell blank PCBs for the DIY crowd. I'm not sure how the DP-25 is calibrated, but I'm imagining a bunch of trim pots 

[dom0]

I'm not sure how the DP-25 is calibrated, but I'm imagining a bunch of trim pots 

Probably a few trimpots and caps for frequency response and one or more trimpots for CMRR. Calibrating diff probes is not simple.

[pascal_sweden]

Aren't the DP-30HS or DP-40LV a better choice than the DP-25 for low voltage measurements?

Best sensitivity: DP-30HS (1mVrms)
Widest bandwidth: DP-40LV (40 Mhz)

DP-25: 1000V, 25MHz, 20mVrms
DP-30HS: 65V, 30MHz, 1mVrms
DP-40LV: 650V, 40MHz, 10mVrms

http://www.pintek.com.tw/files/pintek/PROBE-COMPARISON-CHART_2.pdf

http://www.pintek.com.tw/files/pintek/DP-65-25-frond.pdf
http://www.pintek.com.tw/files/pintek/DP-30HS-40LV-DM-frond.jpg

http://www.globalmediapro.com/dp/A01LT0/Pintek-DP-25-Differential-Probe-25MHz-1000V/
http://www.globalmediapro.com/dp/A25XX7/Pintek-DP-30HS-Differential-Probe-30MHz-65V/
http://www.globalmediapro.com/dp/A25XY5/Pintek-DP-40LV-Differential-Probe-40MHz-650V/

Only a pity that they don't have the low voltage (65V) high sensitivity (1mVrms) differential probe in 100MHz version. If you would have 4 of those differential probes, you could turn your hacked DS1054Z into a fully-fledged 4-channel 100MHz digital isolated scope This would be a unique piece of equipment!

I am going to order DP-30HS. More than one most likely.
Additional plus: The white color suits better with the Rigol scope

[dadler]

Yes, for low voltage measurements. But they are more expensive, and then you need a second one for high voltage. The 40-LV sits in the middle, but it's more expensive as well. I thought price was your issue, based upon your posts? The DP-25 is the lowest priced PINTEK diff probe.

[pascal_sweden]

I have contacted Pintek to bring up the suggestion of a new probe and they provided pleasant feedback

Here was my message:

Hello,

I read more information about the DP-30HS differential probe.

Really nice feature set.

Only a pity that you don't have the low voltage (65V) high sensitivity (1mVrms) differential probe in 100MHz version. If you would have 4 of those differential probes, you could turn an upgraded Rigol DS1054Z into a fully-fledged 4-channel 100MHz digital isolated scope This would be a unique piece of equipment!

Why does high bandwidth (100 MHz) always go hand in hand with high voltages (+1KV)?

Do you see my point about low voltage, high speed differential probe with 100 MHz?
It could turn every hobbyist's 100 MHz scope into an isolated scope, without loosing bandwidth. Hobbyists working on digital design projects, need the bandwidth, and at same time can make mistakes when measuring in their circuits. So I believe it makes sense.

Regards,

Pascal

Here is their feedback:

Dear Pascal,

Thank you for your e-mail.

I have passed your info to our engineer.

We will develop a new model of different probe.

The spec is:

Bandwidth: 100MHz,
Voltage: 65V
Sensitivity: 1mVrms

By the way, can you please let me know your location? In Europe? Or US?

Thank you
PINTEK ELECTRONICS CO., LTD

[akis]

Could you guess the price for such a single probe?

[tomy983]

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.

I know this guy, he is now 70+. He used to work as an electrician on his own, probably doing a good enough job considering that he was doing it forever.
He does not have any considerable education, he just probably learned on the job.

Well, is not like I would do the same or I want to encourage anyone, but to look for the hot wire this guy used to lick his finger and touch the live copper until he felt it... Here we have 230V 50hz.

Everyone who saw him doing it including myself, many many times, tried to persuade him not to, but he just kept going...

He is still alive though.

That is very dangerous though and no one should do it.
 

[electr_peter]

Electricians are a special breed selected from people who have very resistive/thick skin and can touch live mains without dying.
It is half joke, of course. But this statement is true in same sense as "marathon runners never die during marathon because everybody who can die already have done it or stopped running". Some people die running marathon, thus they cannot be marathon runners.

[akis]

And professional gas men testing for gas leaks by running a lighter across the length of an old iron pipe I seem to remember.

[Galenbo]

All this still doesn't make 12V dangerous.

[DanielS]

All this still doesn't make 12V dangerous.

Until you accidentally weld one of your rings or other metallic accessories to 200A bus-bars or other high-current source.

Low voltages are not necessarily harmless.

[dom0]

Won't electrocute you, though. It's the hot, sparking, molten metal hurting you, not the current. Or voltage.

 

[electr_peter]

Won't electrocute you, though. It's the hot, sparking, molten metal hurting you, not the current. Or voltage.
 

Add fire (things get really HOT) to the mix.

[Rupunzell]

The vast majority of two channel Tektronix analog scopes or plug ins have the invert/add switch (select invert, add then drive the two probes common mode and use the gain adjust to optimize common mode rejection. This results in 60 to 20 db of CMR depending on frequency, probe match and ...). This effectively makes a single channel diff input scope. Many of the same Tek input amplifiers have up to 5volts/div, adding a 10x probe makes 50 volts per division with reasonable common mode rejection (keep increasing the gain until the input amplifiers complain).  The tube Tek scopes aka 500 series plug ins often have 10volts/division or more and their over drive capability is something to behold. A few hundred volts on the plate supply goes a long way to help the dynamic range of vertical amplifiers.


Bernice

[akis]

How does that work. Do you get two traces on the screen?

My digital scope does this by using the "maths" function so I choose, say X - Y, but it then plots a third trace which is not easy to see with another two traces already on the screen. Plus, it records no measurements on this third trace so you will have to count squares on the screen...

[dom0]

How does that work. Do you get two traces on the screen?

https://en.wikipedia.org/wiki/Operational_amplifier_applications#Summing_amplifier

[Galenbo]

All this still doesn't make 12V dangerous.

Until you accidentally weld one of your rings or other metallic accessories to 200A bus-bars or other high-current source.

Low voltages are not necessarily harmless.

Please express 200A as 'current', not as 'voltage'
Even 1V 1mA can be dangerous, if you touch it and someone heated the surface up to 200 degrees celcius. Or if there's a dangerous chemical substance in the air around it. Please try to be specific.

[pascal_sweden]

I have ordered two Pintek DP-30HS differential probes, and I am waiting on their arrival
Will provide feedback on their performance after doing some tests.

Pintek promised to keep me up to date on their new development of low-voltage, high-sensitivity, 100 MHz differential probe. Will keep you updated.

[tautech]

I have ordered two Pintek DP-30HS differential probes, and I am waiting on their arrival
Will provide feedback on their performance after doing some tests.

Pintek promised to keep me up to date on their new development of low-voltage, high-sensitivity, 100 MHz differential probe. Will keep you updated.

@pascal
Any updates for us?

[dadler]

I have ordered two Pintek DP-30HS differential probes, and I am waiting on their arrival
Will provide feedback on their performance after doing some tests.

Pintek promised to keep me up to date on their new development of low-voltage, high-sensitivity, 100 MHz differential probe. Will keep you updated.

Where did you find the DP-30HS for sale?

All I can find is this: https://www.globalmediapro.com/dp/A25XX7/Pintek-DP-30HS-Differential-Probe-30MHz-65V/

Which seems ok, but these fine folks only take wire transfers as a method of payment.

I haven't sent a wire transfer in at least 10 years... Makes me a bit uncomfortable but they seem reputable?

[tautech]

I have ordered two Pintek DP-30HS differential probes, and I am waiting on their arrival
Will provide feedback on their performance after doing some tests.

Pintek promised to keep me up to date on their new development of low-voltage, high-sensitivity, 100 MHz differential probe. Will keep you updated.

Where did you find the DP-30HS for sale?

All I can find is this: https://www.globalmediapro.com/dp/A25XX7/Pintek-DP-30HS-Differential-Probe-30MHz-65V/

Which seems ok, but these fine folks only take wire transfers as a method of payment.

I haven't sent a wire transfer in at least 10 years... Makes me a bit uncomfortable but they seem reputable?

Be aware there are 2 versions, the original Pintek and Pintech.
RS sell them but out of stock. http://uk.rs-online.com/web/p/oscilloscope-probes/7296671/

Na, most will send you a Invoice with bank details and you just set up a DC to their bank from yours and just pay the fees. 

[McBryce]

Hi,
    I just picked up the July/August edition of Elektor Electronics and they have released a design for a "2GHz Active Differential Probe". I haven't had a chance to take a proper look at it yet (life gets in the way once again). Has anyone else checked this out yet? Any opinions on the circuit / design?

McBryce.

Side Note: For some reason Elektor have decided not to do the usual "Summer Bumper Edition" with 100+ circuits etc. as they have done since as long as I can remember. Pity really, Elektor seems to be offering less and less and costing ever more over the last few years.