12
\$\begingroup\$

I notice that clamp-type current meters range in price from a few dozen dollars to a few hundred, but current probes for oscilloscopes cost significantly more, with many close to $1000 and some well over $4000. Why are the oscilloscope current probes so expensive? Are they built by princes? Do they contain coils of solid gold wire?

I get that these are fairly low-volume items, and that they need to be calibrated and probably have circuitry that compensates for various errors, but isn't that also true of current meters? Is there something special about the probes, or just market forces at work?

\$\endgroup\$
9
\$\begingroup\$

I believe there are two components at play here:

1 - Clamp-type current meters are much simpler devices because they only need to measure the amplitude of an AC current at a particular low frequencies (some measure DC, but are more expensive). Current probes (especially those with ability to measure DC) are much more sophisticated, having to provide flat response over a decent frequency range and being much more susceptible to all sorts of calibration problems and drifts.

2 - The market for clamp-type current meters is way bigger than the market for current probes, since it's used by electricians, which is a much bigger universe than the one represented by electronic engineers and technicians.

Hey... maybe there is a market opportunity here. Whoever comes up with a more affordable current probe may find a good market among hobbyists and small businesses.

\$\endgroup\$
  • 5
    \$\begingroup\$ Bandwidth is also a major factor. High bandwidth current measurement is extremely difficult without using a sense resistor (and thus converting it to voltage measurement). Clamp meters only have to worry about mains frequencies, for the most part, so they don't need to go much above 400 Hz. Scope probes go well into the MHz. \$\endgroup\$ – Hearth Apr 21 at 14:12
5
\$\begingroup\$

Well, first of all, DC-capable probes are a bit more expensive because they have to use Hall Effect sensors and deal with small offset voltages. But apart from that, there are three reasons:

  1. Bandwidth
  2. Bandwidth
  3. Bandwidth

High bandwidth AC-DC probes work by sandwiching a Hall effect sensor in a magnetic core. If you want 20 MHz of bandwidth, you need to find a Hall effect sensor with 20 MHz bandwidth, or, you need to do some fancy blend of inductive coupling at high frequencies plus Hall effect at low frequencies, and maintain accurate response across the whole range.

A low-cost AC-only probe with limited bandwidth may just be a current transformer.

\$\endgroup\$
4
\$\begingroup\$

Terms like upper/lower frequency, peak A range, sensitivity and linearity can be very cheap in Hall Effect Sensors, and Op Amps with high gain-BW are cheap.

  • We know the cost increases greatly to get a DC response in a clamp with very high sensitivity.
  • We know there are some tradeoffs with dynamic range, calibration, saturation, linearity and Remenance.
  • Why/how are ferrite probes better? and why more expensive?
  • How difficult is the ferrite air-gap for high permeability ferrite cores for measurements of current
  • how does this relate to $ vs \$(gain\cdot BW\cdot Amps)/(sensitivity\cdot accuracy)\$

    Let's consider a few of leading Keysight current-probes in this $ range for a measure of sensitivity to these parameters for market price. Firstly, organize a list of parameters.

    KEYSIGHT CURRENT PROBES, US$ for output to 1 MΩ BNC


    N7042A Rogowski AC    $ 1,881  9.2 Hz ~ 30 MHz   20 mV/A   300 Apk        
    N7041A Rogowski AC    $ 1,881 12   Hz ~ 30 MHz   10 mV/A   600 Apk     
    N7040A Rogowski AC    $ 1,881  3   Hz ~ 23 MHz    2 mV/A  3000 Apk     
    N7026A AC/DC clamp    $ 5,016          150 MHz 1000 mV/A    40 Apk    30 Arms
    1146B                 $   685          0.1 MHz  100 mV/A   100 mA ~ 10 Apk          
                                                  10 mV/A   1A     ~100 Apk    
    N2893A  AC/DC         $ 3,999          100 MHz  100 mV/A    30 Apk   15 A    
    1147B   AC/DC         $ 2,526           50 MHz  100 mV/A   30 Apk 15 A    
    N2821A  AC/DC         $ 3,226            3 MHz     1 V/A  50 uA - 5 A        
    N2820A  AC/DC 2-ch    $ 4,302            3 MHz     1 V/A  50 uA - 5 A     
    N2783B  AC/DC         $ 3,221          100 MHz   0.1 V/A  50 Apk      30 Arms
    N2782B  AC/DC         $ 2,840           50 MHz   0.1 V/A  50 Apk      30 Arms
    N2781B  AC/DC         $ 4,333           10 MHz   10 mV/A  300 Apk     150 Arms
    N2780B  AC/DC         $ 5,358        2 MHz   10 mV/A  700 Apk     500 Arms
    

    (this answer will be a work in progress, and this text deleted when completed)

  • in the meantime , some may reconsider that BW is the only driver,

  • why is the most expensive only limited to 2MHz?
  • yet a less costly Rogowski coil good up 30MHz

ref: https://www.keysight.com/en/pc-1659326/oscilloscope-probes?pm=SC&nid=-32553.0&cc=US&lc=eng

\$\endgroup\$
  • \$\begingroup\$ Current rating seems to be important also, a point I hadn't really considered because when I have shopped for probes, I was not looking for such high current. The Rogowski coil is AC coupled. \$\endgroup\$ – mkeith Apr 21 at 20:59
3
\$\begingroup\$

Cheap clamp current meters can only measure quasi-constant current with variations noticeable on a human timescale (seconds or single-digit Hertz). Current probes have frequency responses starting at hundreds of kHz and going up to hundreds of MHz for the expensive ones. That's a difference of 3 to 6 orders of magnitude.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.