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weird but seemingly familiar looking symbol

I decided to start a new question because I have no idea what word describes it at best, let alone to do a research (aka googling) which can be a bit inconclusive.

At first glance, it looks like it convincingly represents an LED, albeit not with the proper LED symbol (there is a diode symbol at the bottom, which makes sense.) Also the epoxy lens/dome and the die. Yup, it is closely modeled after a classical 3mm/5mm LED light.

Right?

Well, here comes the doubt. This symbol is often found on analog volt meters. (I found mine in an automatic voltage regulator) but I'm sure that this symbol might be around on other devices. Interestingly enough, the devices that bear this symbol often don't directly involve any LEDs besides indicator lights (the AVR in the picture doesn't even have one.)

What does this symbol mean?

nitro2k01
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Yudhi G.
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    The symbol is WAY older than LEDs – fraxinus Aug 25 '22 at 15:25
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    The answers below are excellent and say it all, but I wanted to comment on another aspect of your question where you write "I have no idea what word describes it at best, let alone to do a research (aka googling) ", so try this: "symbols on analog meter". Adding the keyword "analog" leads you in the right direction. – P2000 Aug 26 '22 at 05:00
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    I absolutely know it's not this, but that symbol pair really *should* represent a tunnel diode! (just look at the two together) :-) – abligh Aug 27 '22 at 05:38

3 Answers3

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That's the meter type, PMMC (Permanent Magnet Moving Coil) with rectifier.

The first symbol means it's an AC meter (which is why it has a rectifier), the 5.0 is the accuracy (percentage of full scale), and the last one is Attention, observe the instructions for use.

GodJihyo
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  • Well thank you! Never expected it to look like an LED or something. With the rise of digital meters these kind of symbols are disappearing from the curriculum. – Yudhi G. Aug 25 '22 at 08:06
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    That is not the symbol for an LED (Light emiting diode) an LED has little rays going away. It's the symbol for an diode - the non light emiting type – Christian Aug 25 '22 at 15:21
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    fun fact: even non-light-emitting diodes do emit (and absorb!) infrared light. Which is why they're put inside black plastic cases. If you have a 1N4148 on hand (glass case) you can introduce noise into your circuit by exposing it to light. – user253751 Aug 26 '22 at 17:29
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Here's a list of the symbols generally marked on panel meter dials.

enter image description here

vu2nan
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-4

The moving coil meter is shunted with a silicon diode(0.7 volt barrier) for protecting the coil from high voltages. The diode ensures that the voltage across the coil does not exceed 0.7 V.

vu2nan
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jm ravindran
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    The diode symbol means that it is an AC meter that uses a DC movement and a rectifier diode as opposed to other methods such as hot wire, thermocouple, electrodynamometer, or moving iron vane. The rectifier in older ones is often a copper oxide type. While diodes are sometimes used to protect a meter, that is not what the symbol here means. – GodJihyo Aug 27 '22 at 12:20
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    @jm ravindram Please read GodJihyo's comment and consider whether your anser should be modified or deleted. If you wish to claim that it shows a protection diode please add a reference. – Russell McMahon Aug 27 '22 at 12:42