By far the most used oscilloscope probes are the passive 10:1 attenuation probe. Next step in probe categories are active probes.
Active probes succeed in practically eliminating reactive loading of the circuit under investigation by means of a small solid-state amplifier in the probe body adjacent to the tip.
There are two main classes of signals we electronics engineers care about: single-ended and differential-mode. With single-ended connection, the signal is carried on a single wire, which is defined as being referenced to the common system ground. Single-ended connection is usually quite easy to measure with normal oscilloscope probe. Differential-mode signalling uses a pair of wires, where the voltage difference between the wires forms the signal
Differential probes are oscilloscope probes designed to measure the difference between two signals. Differential probes allow a standard bench-type oscilloscope to be used to measure the voltage between two terminals. Both are referenced to but float above the electrical system ground potential. This cannot be done using a single-ended probe.
Differential probes are optimized to acquire only the differential signal between two test points, always reject (i.e. do not measure or display) any common mode signal. Early designs consisted of a pair of passive probes terminated at a differential amplifier located as a separate device adjacent to the oscilloscope Some modern scopes can calculate and display the difference without extra hardware. For probing differential signals, it is possible to use a pair of probes, one for each signal wire, and then utilise the scope’s math difference function to show the signal. This is quite often a desperate measure, and what you really want is a differential front-end in hardware. You need a differential active probe.
There are different differential probes for different applications. For fast digital signal measurements engineers need differential probes that can handle very fast signals at few volts amplitude. There are several brands of differential input oscilloscopes available. Differential signaling used in high speed serial standards requires very accurate characterization.
The engineers that need to measure mains voltage circuits and power supplies need differential probes that can handle voltages up to hundreds of volts. Because of the electrical environment within which they are used, differential probes in some applications are required to have higher voltage ratings, typically 600 V. Differential oscilloscope probe eradicates the problem of making accurate voltage waveform measurements on circuit elements that are not ground-referenced, without the risk of short circuits that could damage the device under test or the measuring instrument. These probes are the best choice for making non-ground referenced, floating or isolated measurements in large part due to their common mode rejection capability.
A Differential Probe Guide – How & Why To Use a Differential Probe With Your Oscilloscope
EVblog #279 – How NOT To Blow Up Your Oscilloscope!
EVblog #932 – How Does A HV Differential Probe Work?
(#0032) High Voltage Oscilloscope Probe Design – DRSSTC vs. Spark Gap #04 – Modding a 1kV differential scope probe to measure 20kV
https://www.testandmeasurementtips.com/basics-of-active-and-differential-scope-probes-faq/
https://hackaday.com/2021/12/12/differential-probe-clocks-at-100mhz-and-200/
https://hackaday.com/2021/08/25/this-modular-differential-probe-shows-great-attention-to-detail/
https://hackaday.com/2016/03/31/diy-active-sub-ghz-differential-scope-probe/
15 Comments
Tomi Engdahl says:
Use two channels and internal math or active/differential probe.
Tomi Engdahl says:
https://circuitcellar.com/research-design-hub/high-voltage-differential-probe/
five nights at freddy's says:
Utilize two channels as well as internal math or an active/differential probe.
https://fivenightsatfreddys.online
Tomi Engdahl says:
EEVblog #1368 – Active Oscilloscope Probes COMPARED (Part 2)
https://www.youtube.com/watch?v=WlSb8hdFtTY
Tomi Engdahl says:
How to Make a DIY Differential Oscilloscope Probe
https://www.youtube.com/watch?v=zQDLY-ot4eo
For an upcoming project, Industry Expert Consultant Mark Harris needs a differential probe that can handle high voltages. But finding one to suit his needs is an expensive endeavor. Join Mark as he goes the DIY route with this differential oscilloscope probe project.
0:00 Intro
0:31 What is a Differential Probe?
1:34 Our Differential Probe Overview
3:07 Board Layout & Assembly
5:20 Circuit Alterations
6:41 Testing
10:03 Isolating the Issue
12:10 Checking the Probe’s Response
12:56 Wrapping Up
Tomi Engdahl says:
DL-ISO: High Voltage Optically Isolated Probes
https://teledynelecroy.com/probes/power-probes.aspx?wvideo=jxgrs4i8vf#dl-iso
Tomi Engdahl says:
EEVblog 1521 – Common Mode Rejection Explained & Measured (CMRR)
https://www.youtube.com/watch?v=vDe_BHvRpks
What is Common Mode Rejection Ratio (CMRR) and how to measure it on a high voltage differential probe or differential amplifier. Using the new Rohde & Schwarz MXO4 oscilloscope.
00:00 – What is CMRR?
01:53 – Why twist the wires?
03:26 – Typical CMRR figures
04:51 – How to measure CMRR – The Setup
08:54 – Remote R&S Oscilloscope desktop view & settings
11:22 – Output to input voltage ratio
11:58 – Beware of DC offset
13:36 – Does the 20MHz CMRR measaurement match?
14:02 – Input referred measurement
15:02 – Compensating for the gain
16:29 – Automated Frequency Response Analysis
https://www.eevblog.com/forum/blog/eevblog-1521-how-to-measure-differential-probe-cmrr/
Tomi Engdahl says:
EEVblog #932 – How Does A HV Differential Probe Work?
https://www.youtube.com/watch?v=GOlgaEK2Hsk
Tomi Engdahl says:
Single-Ended or Differential Probe? Take the Mystery Out of Oscilloscope Probing
https://www.youtube.com/watch?v=a28lVMsWFEY
Differential probes aren’t just for differential signals!
What is a differential probe? It’s a probe designed to measure a differential signal. But why are engineers everywhere using differential probes as general purpose measurement tools? Join Ally as she unveils this oscilloscope probing mystery.
Learn the three main values of a differential probe:
#1: Differential probes have a high common mode rejection ratio
#2 Probe loading is reduced with a differential probe
#3 Differential probes have higher bandwidth than single-ended probes
Tomi Engdahl says:
EEVblog 1521 – Common Mode Rejection Explained & Measured (CMRR)
https://www.youtube.com/watch?v=vDe_BHvRpks&t=908s
What is Common Mode Rejection Ratio (CMRR) and how to measure it on a high voltage differential probe or differential amplifier. Using the new Rohde & Schwarz MXO4 oscilloscope.
00:00 – What is CMRR?
01:53 – Why twist the wires?
03:26 – Typical CMRR figures
04:51 – How to measure CMRR – The Setup
08:54 – Remote R&S Oscilloscope desktop view & settings
11:22 – Output to input voltage ratio
11:58 – Beware of DC offset
13:36 – Does the 20MHz CMRR measaurement match?
14:02 – Input referred measurement
15:02 – Compensating for the gain
16:29 – Automated Frequency Response Analysis
https://www.eevblog.com/forum/blog/eevblog-1521-how-to-measure-differential-probe-cmrr/
Tomi Engdahl says:
HVFO: High Voltage Fiber Optically-isolated Probes
https://teledynelecroy.com/probes/power-probes.aspx?wvideo=jxgrs4i8vf#dl-iso
The new HVFO108, with 150 MHz of bandwidth, is suitable for both Silicon and Silicon Carbide designs. It is designed to measure small signals floating on an HV bus and delivers excellent performance, has high CMRR, and provides optical isolation to reduce DUT loading.
Tomi Engdahl says:
https://www.hackster.io/news/build-a-10x-100mhz-differential-probe-for-signals-embedded-in-common-mode-voltages-1450268eceec
Tomi Engdahl says:
DIY Active Differential Probe for the oscilloscope | Do-it-yourself electronics
https://www.youtube.com/watch?v=qY7B09teGX4
An active #differential #probe designed for the measurement and visualization of waveforms of mains voltage (or at mains’ voltage level) on a common #oscilloscope without running the risk of frying the scope, the probe, or worst yourself!
In a previous video (here: • Easy DIY passive … ) I’ve showcased a passive probe, unlike that one this active probe uses only one input channel of the oscilloscope.
The probe run on a 9V battery that lasts about 20 hours (based on Duracell’s data sheet calculated for the current drawn by the circuit.)
It features an input impedance greater than 4MΩ, an output impedance of ~50Ω and an attenuation ratio of x200 (200:1). The theoretical maximum input voltage is 800Vp (given by the voltage limit of the resistors used in the attenuator). This allows to take measurements not only on common 230/240Vrms but even at 380/400Vrms (used in Europe), including phase-to-phase on a three phases system.
BEWARE that if you try to make this project yourself you’ll do it under your own sole responsibility, I’ll take no liabilities! Keep in mind that the circuit’s performance and limits heavily depends by the components used and how the circuit has been made. I mounted two of the four resistors of the attenuator on the PCB and has been covered with an insulating resin that is NOT visible in the pictures.
The probe is built around an LM4562 in IA configuration, and a resistive attenuator. Tests confirmed that there is no need for capacitive compensation since the input capacitance is remarkably low (less than 2pF) and the frequency range of interest is about mains frequency (50/60Hz) and its harmonics, so rarely there is the need to read frequencies above 20Khz.
I hadn’t the possibility to test the probe for its actual bandwidth, though.
For the sake of simplicity I used common 1% resistors (with 20ppm/C) rated 250V. The “high” voltage must be well separated by the low voltage part. The key point of this probe is the link to ground, or PE (Protective Earth) that provides its safety. It works on both TT and TN systems. The PE is also carried by the oscilloscope, but the provision of a separate connection for grounding (the green banana socket) is important in the case of fault of the cable, the use of a battery powered oscilloscope and the case when the plug is disconnected from the scope.
This probe MUST NOT be used where the line is not protected by a GFCI, RCD or RCCB.
Easy DIY passive #probe to measure #mains with the #oscilloscope
https://www.youtube.com/watch?v=XGW_aqE4PVc
Do you have to measure mains voltage waveform just once in your whole life? Differential probes are too expensive? Here it is a simple, cheap, DIY solution.
CAUTION: Working on mains voltage is dangerous, you MUST know what you do.
Directly using the probes of the oscilloscope to measure the mains is hazardous, it could lead to from destroying your probes to melting the traces of the PCB inside your oscilloscope, not to mention the risk of being injured. Depending by the grid system you may have 50% to 100% chance of causing a short capable to destroy your instrumentation.
In an old video I presented a depth analysis of why you can blow up your oscilloscope while making measurements at mains, follow this link: • Correct use of th…
Also the trick that uses two probes directly may end up in catastrophic results if you work on voltages above 110V RMS.
In this video is presented a simple attenuator made of just 1/4W resistors, that guarantees safe operations with the oscilloscope provided the PE (Protective Earth, the yellow-green/green wire) is actually tied to ground. It still requires two input channels of your oscilloscope but it is safer than directly hooking the probes to the mains.
Tomi Engdahl says:
A differential probe, a device for measuring the voltage between two points in a circuit rather than the voltage between a point and ground, it an extremely useful addition to any electronics bench. Inside such a probe you’ll usually find a fancy op-amp working as a differential amplifier, and for correct operation they require careful adjustment to null out DC bias and achieve the maximum common mode rejection….
HACKADAY PRIZE 2023: THIS DIFFERENTIAL SCOPE PROBE IS SMARTER THAN IT LOOKS
https://hackaday.com/2023/09/28/hackaday-prize-2023-this-differential-scope-probe-is-smarter-than-it-looks/?fbclid=IwAR39WOWdQdFvKcOQ0R8dXwK6qkgMCsBdHuH1lZ0nkFIs4vfBMW_cQPaDSRA
A differential probe, a device for measuring the voltage between two points in a circuit rather than the voltage between a point and ground, it an extremely useful addition to any electronics bench. Inside such a probe you’ll usually find a fancy op-amp working as a differential amplifier, and for correct operation they require careful adjustment to null out DC bias and achieve the maximum common mode rejection. We particularly like [Craig D]’s probe, because these adjustments are taken care of automatically by a microcontroller.
https://hackaday.io/project/191837-pd150
Build Now GG says:
Thanks for sharing exactly the problem I was looking to solve!