NO Reed switch in a magnetic field?

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Discussion Overview

The discussion revolves around the behavior of reed switches in magnetic fields, particularly focusing on normally open (NO) reed switches and their operation in both changing and steady magnetic fields. Participants also explore the potential use of Hall sensors as an alternative to reed switches, discussing their characteristics and wiring considerations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Homework-related

Main Points Raised

  • Robin questions whether a normally open reed switch would close in the presence of a steady magnetic field, seeking clarification on its behavior.
  • Dave states that a reed switch normally operates in a non-changing magnetic field and will remain closed if a magnet is held close.
  • Another participant explains that applying DC to a solenoid creates a steady magnetic field that keeps the reed switch closed until the field is turned off.
  • Mike provides information on Hall sensors, detailing their operation, power requirements, and output characteristics compared to reed switches.
  • Robin expresses confusion regarding the terminology of reed switches, specifically the terms 'must operate' and 'must release,' and how they relate to normally open and normally closed states.

Areas of Agreement / Disagreement

Participants generally agree on the operation of reed switches in steady magnetic fields, but there is some confusion regarding the specific terminology and characteristics of different types of reed switches. The discussion on Hall sensors introduces additional complexity, with varying opinions on their advantages and disadvantages compared to reed switches.

Contextual Notes

There are unresolved questions regarding the definitions of 'must operate' and 'must release' in the context of reed switches, which may depend on specific models or manufacturer specifications. Additionally, the discussion does not reach a consensus on the best choice between reed switches and Hall sensors for particular applications.

Who May Find This Useful

This discussion may be useful for individuals interested in electrical engineering, sensor technology, or those working on projects involving magnetic switches and sensors.

Robin07
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NO Reed switch in magnetic field. What I'm wondering is, a normaly open switch is closed in the presents of a changing magnetic field. Would the switch be closed when the field is present but not changing? I'd rather use a Hall sensor but know very little in how I would hook that up to my reed switch and the DC power supply. Frist, I guess how does a NO reed swich behave. Any one?

Thanks for your responses
Robin Hooper
 
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Hi Robin

A reed switch NORMALLY operates in a non-changing magnetic field ie. if you hold a magnet close to a reed switch and leave it there in position and the reed will stay closed

Dave
 
You apply DC to the solenoid, this creates a steady magnetic field and causes the reed switch to be held closed. The reed stays that way until you switch off the field.
 
Thanks guys, exactly the answer I was looking for, just needed it to be confirmed.

Many Thanks
Robin
 
Most Hall modern hall sensors are easy to use, the pin devices. It will have a pin for ground, another for power, and a third to tell you when the field is present.
Most run off of 3-5 volts and have what's called on open collector or open drain output.
This means that the output appears disconnected when no field is present, but is shorted to ground when a field is present.
The output is not as tough as your reed switch in that it can usually only handle a few tens of milliamps. Also, you cannot "pull" the output voltage above the devices supply voltage without fear of damage.

These parts are much smaller, somewhat cheaper, and are usually sensitive to which pole is facing them. Unlike the reed relay, they can be toggled for the life of the instrument without fear of wear.
There are numerous variations for mounting alternatives, output signal alternatives, sensitivity, operating voltage and so forth. Digi-Key is a good place to search, find data sheets, and/or buy them.
 
An informative reply, thanks Mike.

I'm not an electrical anything but you gave me food for thought, a direction allways helps.
 
So I went to Didikey and found some reed switches. Some of the choices are 'must operate' and 'must release'. I imagine this is where ones choices NO or NC. and that is what I'm not able to decifer between the two states. What's confusing is that one type lists 'must operate' but does not indicate 'must release'. Which is which?

Thanks for all your help thus far
Robin
 
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