Reed Switch Normally Open or Normally Close

Electromechanical Switches
,
1

I have an application that requires a reed switch to sense a door closing. The door has a neodymium magnet embedded into it and when the door is closed, I want the reed switch to be open (open circuit) and when the door is open, I want the reed switch to be closed (shorted - i.e. closed circuit). I proceeded to purchase two reed switches from Digikey just to make sure:

a SPST NC switch:

and a SPST NO Switch:

I received them today and tested them with my magnet. Unfortunately, both behave as a NO (Normally Open switch). My understanding is that the MK15-B-2-OE/2765323 which is listed as an NC (Normally closed) should be shorted when NO magnet is present. This is the behavior I need for my circuit.

I’m I missing something is my definition of NC and NO incorrect? I took a closeup image of both of them, just to make sure that the parts were inventoried correctly and their marking identify them correctly.

Mark

2

Here is an image of the two reed switches:

image
image1266×671 63.9 KB

3

Hello,
Welcome to the DigiKey tech forum. You’re correct on the description of your switch function. Looking at the datasheet part MK15-B-2-OE is listed as NC. Did you follow the information on the datasheet showing magnet and switch placement, poles and spacing? The magnet may also be an issue, does the magnet you’re using fall within the recommendations listed on the datasheet ?

1 Like
4

You are correct, an NC reed switch should read shorted when no magnet is nearby.

If it reads open when no magnet is around and then closes when you bring a magnet close, it is an NO switch.

Here’s the latest data sheet for the part:

1 Like