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I do not know what "NM" indicates here under this inductor/ferrite bead label L5?enter image description here

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  • \$\begingroup\$ I've never seen NM, I've seen NL for not loaded. \$\endgroup\$
    – Voltage Spike
    Commented Jul 16, 2019 at 3:48
  • \$\begingroup\$ perhaps non-magnetic? - IE air core \$\endgroup\$ Commented Jul 16, 2019 at 8:42

3 Answers 3

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Maybe "NO MOUNT"? Is the supply connection optional?

“Non-Magnetic” doesn’t make sense, at least at first look. All inductors are “magnetic” in that they use flux to work. That’s said, I could see how they meant that as a stand-in for air core, so I’ll pile on to that answer too.

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    \$\begingroup\$ I read it a "Not Mounted". \$\endgroup\$
    – Justme
    Commented Jul 16, 2019 at 7:18
  • \$\begingroup\$ I think not mounted is a good conjecture, but indeed this part is mounted in the circuit, and the temperature sensor is necessary for proper function of the main IC. \$\endgroup\$ Commented Jul 16, 2019 at 13:58
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I'm guessing it means "Non-Magnetic" - as in "air-core" in lieu of "iron-core". There might be a particular RF frequency that the designer was trying to filter. However, I would guess that the designer was trying to filter all interference judging by the use of 4 sizes/types of filter caps on the power rail.

But, really - I doubt an NM air-core inductor is the most effective solution for the context of the circuit above. Instead, I would omit the confusion caused by the label "NM". And, I may have more clearly labeled the circuit as a low-pass LC filter.

LC filter: If there were no annotations on the circuit diagram at all, I would have said "L5" was a 120 ohm ferrite bead such as Digikey: https://www.digikey.com/products/en?keywords=742792023. I have found this type of "bead" in schematics as a stop-gap way to create an analog power rail from a switching power supply rail (as shown below).

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I cannot say definitively, but I believe the most probably meaning of this label is "non-magnetic".

This is because "non-mounted" would mean the temperature sensor power supply is not connected, which would cause the main IC to fail, since it needs proper temperature regulation to operate. I traced the signal line to the component on the physical board, and indeed it is mounted.

Also, there are other inductor symbols in the schematic which do show the inductance value, and they have a different symbol. Specifically, they include two lines above the arches of the inductor symbol, as opposed to no lines above. This would indicate to me iron-core vs. air-core:

enter image description here

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