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Portable Clamp Meter

My current (perhaps outdated) knowledge tells me that portable current clamp meters are meant for high current readings only. Can portable current clamp meters measure down to uA-range, or even nA-range readings?

I've measured pA and nA currents through lab equipment before, but bringing them out in the field is not an option this time.

To add, the wires from which the measurement are to be taken are short and rigidly mounted. As such, current magnification through looping is not possible. For this, I'd like to ask for techniques in non-invasive nA-range current (expecting 10nA minimum reading)using a plain current clamp meter with a minimum measurement capability of 10mA.

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    \$\begingroup\$ You seem to be asking a shopping question which will result in question closure. Instead edit to ask about what techniques can be used. \$\endgroup\$
    – Transistor
    Mar 25, 2021 at 10:20
  • \$\begingroup\$ Question modified, thanks. B̷̢̹̊u̷̗͒͂t̶̳̀ ̵͔̕I̷̟͕̊̋ ̷̨͈̓a̴̝͓͂m̷͈͂ ̶̭͖̌s̸͕̈́̎t̷̜̃i̵̫̽l̶͎̿͝l̷̹̎ ̸̧̆l̷͕͛o̶̟̽͠w̴͙̄̀k̷̳̟͂͒ě̴̻̞y̸̰̝͗ ̸̝̻̓l̶̨̹̈́̈́o̴̞͗ǫ̷̧̊k̸̪̅ï̶͉͖n̴̨̞̅g̷̜̈́͛ ̶̛̘̓f̶͇̈́o̵̙̟͘r̶̥̋ ̴͈̜̃ả̴̹̽ ̵̩͖̔̾u̴̥̫͛A̵̢̚-̷̳̓͗r̷̰͊a̴̙̹̕n̶͎̰͗̉g̷̦̽̇e̵̖͎͒ ̶̧̮̐͊c̸̞̈́ǔ̴̢̞ŗ̶́͆ŕ̵͔ě̷͎͒n̵̦̗̄t̴̙͉͑ ̸̦̥̆c̶̞̊̊͜l̶̨̊͌ä̸̧̅m̶͘͜͝p̶̰͎͂̏ ̶͓̓ͅm̵͙̝͗é̶̘̠̒t̸͇͐͐ẽ̷͉̼ṟ̸̞̒ ̶͇́̎î̶͈̠f̴̥̖̎͊ ̵̢͎̒p̵̳̘̑͝õ̴̉ͅs̶̠̆ṣ̶̀̾i̴̖͔̒̍b̴̺̰̀͌l̶̢̎̇ḛ̸͕̾ ̴̺̯̽̚l̶͉̩̇̕o̴͈̓l̸͒̎͜ \$\endgroup\$
    – Carla H.
    Mar 25, 2021 at 10:51
  • \$\begingroup\$ DC current? If not, what characteristics does the current have? \$\endgroup\$ Mar 25, 2021 at 12:53
  • \$\begingroup\$ Yes DC current. I was told that it can have transients kick up to around 120A, and sustained DC currents of up to 40A. \$\endgroup\$
    – Carla H.
    Mar 26, 2021 at 2:55

2 Answers 2

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As Damien rightfully mentioned, nA is not the conventional territory of contactless sensing.

However, Magnetoencephalography does this for even smaller current. nA should definitely be possible if you can get close to the current line. If you can get within 1 mm of the line, the magnetic field will be 1µA/m which is about 1.3 pT.

To detect such small magnetic fields, the conventional sensors based on the normal Hall effect are not sensitive enough (not in a straightforward way) but sensors based on ferromagnets are. There are scientific demos of even pT sensitivity and below for such sensors. The sensors that come to mind to possibly detect this are planar Hall sensors and fluxgate sensors allow such precision. To select which sensor might suit you best, it is very important to consider the exact geometry of your current line and sensor. Using a small ring core around the current line with a planar Hall sensor instead of the usual semiconductor Hall sensor should do the trick.

But I am not aware of any commercial device that offers this.

Edit: it should be mentioned that the earth magnetic field is about 50 µT. So nulling + a very stable mount or better yet: magnetic shielding is absolutely mandatory to detect such small current in a non-contact way.

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  • \$\begingroup\$ Hi @tobalt, thanks for this. Honestly, I'm not technically familiar with Magnetoencephalography and I'd need to read up a lot on this. I'm still leaning on solutions and techniques which incorporate more rugged/ portable form-factors. \$\endgroup\$
    – Carla H.
    Mar 26, 2021 at 3:03
  • \$\begingroup\$ Carla H: I don't think that understanding magnetoencephalography is that helpful for your application. I just mentioned it as an example of contactless detection of small current based on their magnetic field. So essentially your problem can be rephrased as a magnetic field detection problem. Searching for this specifically might turn up results faster than looking for noncontact detection of tiny currents. \$\endgroup\$
    – tobalt
    Mar 26, 2021 at 7:38
  • \$\begingroup\$ And if it is possible for you to surround the conductor with a slotted ferrite core, you can enhance the magnetic field by 2-3 orders of magnitude. If you pass the wire through the core several turns, the amplification will be even higher. Though not technically "invasive", this becomes impractical at some point. \$\endgroup\$
    – tobalt
    Mar 26, 2021 at 7:51
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These clamps use a current loop or Hall effect sensors for contactless current sensing. They work by sensing the magnetic field created by the current flowing.

Due to the design, those do not offer very good accuracy, especially in low current and usually only measure from 1 amp and above.

Below 100mA I doubt any device of this design, especially Hall effect-based, would give an accurate reading.

For uA or nA range measurement, it is definitely not the way to go and shunt based measurement should be used.

Current loop working in AC are of better accuracy than Hall-based sensors, especially if it's a closed metalcore or wind directly to the cable that is measured. In this situation, it can reach an acceptable accuracy for a smaller current, but it cannot measure DC.

Hall effect measures the magnetic field, they have strong temperature dependencies and drift easily as the field can vary due to many factors.

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  • \$\begingroup\$ Thanks @Damien. ...drift easily as the field can vary due to many factors. > Even at the lab, I frequently find myself nulling my current probe amplifier. Now I'll be doing this using a portable clamp meter, and out in the field. With uA and nA-range currents too. \$\endgroup\$
    – Carla H.
    Mar 25, 2021 at 11:04

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