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I have some used reed switches with no datasheets. all of them have a black mark on one side. I want to know what does this mark mean?

enter image description here

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  • \$\begingroup\$ A better picture would help a lot! It'd be important to know whether the dots are inside or outside. If inside: it could be some dot of getter metal to remove gases (oxigen, nitrogen)that otherwise would react with (damage) arcing electrodes. \$\endgroup\$ – Curd Aug 24 '17 at 9:34
  • \$\begingroup\$ @Curd dot is a color on outside, all of reed switches have this mark on a same location \$\endgroup\$ – Hadi Barak Aug 24 '17 at 10:23
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They don't. Have a broader look at reeds from other sources. I have a bunch of them here, and install them professionally for burglar alarms. They either have no markings, or sometimes the manufacturer's details. They don't have little black dots. Can I suggest Google Images "reed switch"? You'll see loads of examples, all without black dots. A reed switch is symmetric, non directional or un polarised. They work either way round so don't require one end to be marked.

As to a getter. No. Getters are only for maintaining vacuum. A reed switch contains an inert gas (typically nitrogen). The wiki entry mentions high voltage reed switches that operate in a vacuum, but I don't think that this is one of those.

It could be a testing mark, perhaps maybe. Could also be a spider.

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A normal reed switch should not be orientation dependant.

The paint dot is most likely a manufacturer model code designation.

However a SPDT reed switch has one non (or less) magnetic terminal at the two wire end (the NC terminal).

A normally closed reed switch often is a SPDT type with the NO terminal cut short. In this type the two end wires may have different magnetic characteristics and a dot might provide some strange value. The pictured device looks like a normal NO switch.

While the picture does not show any difference it is possible that in a switch where one terminal is mobile and the other rigid a manufacturer might see fit to mark the relevant end, again I cannot see any use for this information.

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