10

Ammeter front

This is front view of analog ammeter. There are 2 terminals with nut and bolt behind it but nothing marked neither plus nor minus.

winny
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user2681304
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  • This is a cheapie and not legal for use in AC mains. – Harper - Reinstate Monica Apr 13 '20 at 02:11
  • @Harper-ReinstateMonica the markings imply an insulation rating of 2000 volts. – Andy aka Apr 13 '20 at 13:26
  • @Andyaka Which only proves the builder can draw a star. There's no credible data whatsoever to support the idea that it would actually withstand 2000V. When the maker figures out how to draw a slanted ЯU or a UL in circle, then it could be legal as a component or as equipment. – Harper - Reinstate Monica Apr 13 '20 at 20:34
  • I connected it with heater coil in series. Heater coil is rated 220V 2000 watts. In Ameter its showing 10 to 12 Amp current. It was connected for 10 minutes and still woking without any problem. – user2681304 Apr 13 '20 at 23:28

3 Answers3

16

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It's a moving iron meter hence this symbol: -

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Taken from here

Moving iron meters are used for DC AND AC so, the meter needle will only move in a clockwise direction irrespective of current polarity. If it used a magnet it would be polarized and with AC, the needle would barely move (because the needle would try and move clockwise and counter-clockwise at the AC frequency).

It's also worth noting that the symbol that looks like an upside-down "T" next to the moving iron symbol also has a meaning as does the 5 sided star with a 2 inside: -

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Extra picture from here.

Andy aka
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  • I stumbled upon this. I guess this measures the rms value of the current is that correct? Imagine the current is DC plus AC, would it show the rms value always? – user1999 Apr 11 '20 at 14:53
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    @user1999 it would show the true RMS value of DC, AC and AC mixed with DC. – Andy aka Apr 11 '20 at 14:58
14

There are three clues:

  • The scale isn't linear so that implies that it is a moving iron meter.
  • The ≂ symbol indicates that it can handle DC and AC. (The '-' indicates DC and the '~' AC.
  • The terminals are not labelled. If polarity mattered they would be.

The meter can be wired either way.

The moving iron works on the principle that the iron place near the magnet attracts towards it. The force of attraction depends on the strength of the magnetic field and not on its polarity.

See the linked article for a list of advantages and disadvantages of moving-coil meters. They are favoured on cheap electrical devices such as 12 V battery chargers, etc., where they can be considered as a current indicator. Calibration in many cases is going to be terrible.

Transistor
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8

The symbol, circled in red, indicates it's an AC/DC meter.

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vu2nan
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