Looking for a particular a magnetic reed switch - Page 1
Forum section: electronics / beginners

author: Electro Fan
author_rank: Super Contributor
timestamp: October 24, 2022, 04:22:03 am
content: Anyone know where to find a magnetic reed switch that matches these specs (electrical and size) but is NC vs NO?Thanks

author: Electro Fan
author_rank: Super Contributor
timestamp: October 24, 2022, 06:32:14 am
content: Thanks but are you sure? This indicates they might exist:When a magnetic field is brought close enough to the outer casing of the reed switch, the contacts inside are pushed together or apart. This makes or breaks the circuit, depending on the direction of movement. In anormally open reed switch-the most common type- the two contact blades are positioned slightly apart, with an air gap between them. This leaves the circuit they are attached to incomplete until a magnetic force is introduced.In a normally closed switch, the contacts are already touching when at rest. The introduction of a magnetic force instead pushes them apart, breaking the circuit. In either case, the spring force of one or more contact blades returns it to its natural position when not under magnetic pressure.https://uk.rs-online.com/web/generalDisplay.html?id=ideas-and-advice/reed-switches-guide

author: hubi
author_rank: Regular Contributor
timestamp: October 24, 2022, 07:12:04 am
content: Digikey shows 65 SPST-NC reed switches (8 in stock). None of the in stock options match your specs exactly, take a look and see if one of them will work for you.

author: wraper
author_rank: Unknown
timestamp: October 24, 2022, 07:45:49 am
content: There is no NC as such but there are SPDT.https://eu.mouser.com/datasheet/2/240/Littelfuse_Reed_Switches_MDRR_DT_Datasheet_pdf-938344.pdf. The thing is that by it's nature reed switch acts by ferromagnetic plates attracting together in presence of magnetic field. Therefore you cannot get them coming apart. But in SPDT switch NC contact is just a stationary non ferromagnetic contact.

author: wraper
author_rank: Unknown
timestamp: October 24, 2022, 08:02:39 am
content: Quote from: Electro Fan on October 24, 2022, 06:32:14 amThat's some first grade BS. As I said in my previous post, magnetic field does not push them apart. In SPDT reed switches NC contact is not ferromagnetic therefore ferromagnetic NO contact attracts common contact away from NC contact when magnetic field is applied. When you see SPST NC reed switch, it's just a SPDT reed switch with NO contact left unused.

author: SeanB
author_rank: Super Contributor
timestamp: October 24, 2022, 10:28:36 am
content: Yes if you are using it with a pneumatic cylinder you need to either use a separate relay to do the inversion, or arrange the logic to do this. I would guess it is providing limit operation, so you will need to have a relay in any case to drive the valving, so just use a NC contact instead of the NO one. There might be a SPCO reed switch in the range, but those are normally special order items, the vast majority uses the standard reed relay configuration, or you need to use the PNP switch instead and a relay.

author: Electro Fan
author_rank: Super Contributor
timestamp: October 24, 2022, 07:01:33 pm
content: Thanks for all the help. Found something that might work:https://www.ifm.com/us/en/product/MK5156?tab=detailsWill post again if it doesn’t ….Thx again

author: BeBuLamar
author_rank: Super Contributor
timestamp: October 24, 2022, 08:12:38 pm
content: I don't think they make on of the exact same physical dimension but NC switch. If the switch isn't of exact same physical dimension it would be hard to mount on the actuator. I would simply use the NO switch and use a relay to reverse the action of the switch.