Reed Switches and Hall Effect Sensors

 Reed Switches and Hall Effect Sensors

Magnetic sensors are utilized in the whole lot from motors to cellphones.  What magnet must I use with my magnetic sensor?  Should I use a Hall impact sensor or a reed transfer?  How must the magnet be orientated to the sensor?  What tolerances must I be involved with?  Learn extra with a K&J walk-via of specifying a magnet-sensor combination.

What is a Reed Switch?

The reed transfer is an electrical transfer operated via way of means of an applied magnetic subject.  It includes a couple of contacts on ferrous metallic reeds in an hermetic glass envelope.  The contacts are usually open, making no electric contact.  The transfer is actuated (closed) via way of means of bringing a magnet close to the transfer.  Once the magnet is pulled away, the reed transfer will cross again to its authentic position.

What is a Hall Effect Sensor?

A Hall impact sensor is a transducer that varies its output voltage in reaction to modifications in magnetic subject.  In a few ways, Hall impact sensors can in the long run carry out a comparable feature as a reed transfer, however with out a shifting parts.  Think of it as a solid-nation component, properly for virtual applications.

Which of those  sensors is proper in your utility relies upon on some of things.  Factors encompass cost, magnet orientation, frequency variety (reed switches normally are not usable over 10 kHz), sign leap and the layout of the related good judgment circuitry.

Magnet - Sensor Orientation

A key distinction among reed switches and Hall impact sensors is the right orientation required for an activating magnet.  Hall impact sensors set off while a magnetic subject this is perpendicular to the solid-nation sensor is applied.  Most search for the magnet's south pole to be going through an indicated place at the sensor, however test the specification sheet of your sensor.  If you switch the magnet backwards or sideways, the sensor may not set off.

Reed switches are a mechanical tool with shifting parts.  It includes  ferromagnetic wires separated via way of means of a small gap.  In the presence of a magnetic subject this is parallel to the ones wires, they may contact every different, making electric contact.  In different words, the magnetic axis of the magnet must be parallel to the lengthy axis of the reed transfer.  Hamlin, a producer of reed switches, has an excellent utility notice at the subject.  It consists of superb diagrams displaying the regions and orientations wherein the sensor will set off. occupancy sensors and vacancy sensors

It must be referred to that different configurations are viable and frequently used.  For example, Hall impact sensors can hit upon metallic blades of a spinning "fan."  The metallic blades of the fan byskip among a desk bound magnet and desk bound sensor.  When the metallic is among the , the magnetic subject is redirected farfar from the sensor (blocked) and the transfer opens.  When the metallic movements away, the magnet closes the transfer.

What length magnet do I want?

The spec sheet in your sensor must imply the magnetic subject power required to set off the transfer.  This wide variety is normally among 10 and 100 gauss, however test your specs.  Also notice that a few sensors are laid out in AT, or Ampere Turns.  The dating among gauss and AT is complicated, however may be approximated as 1 gauss = 1 AT.  It isn't always perfect, however it'll get you close.  Again, Hamlin has a properly utility notice on this.

For Hall impact sensors, decide the space from the floor of the magnet in which the minimal power requirement is met.  In the video below, we used a Hamlin 55410-3H-02-A Hall impact sensor bought from DigiKey.  The spec sheet shows a normal activation sensitivity of fifty nine gauss.  For a specific magnet, what distance offers me at the least fifty nine gauss?  This query is without problems replied the usage of our Magnet Calculator.  Input the diameter and thickness of a disc magnet, and attempt special distances till it fits the spec wide variety.

In our example, a D42 magnet will create a magnetic subject with a subject power of fifty nine gauss at 0.fifty three inches farfar from the face of the magnet.  In practice, a margin of mistakess is frequently figured in.  A magnet or distance is selected in which the power is nicely above the theoretical wide variety, frequently at 125% or 150% of that value.  Since the sensor stays activated if the sector is nicely above the minimal wide variety, that is a secure practice. electrical sensors and switches

For reed switches, the magnet is placed with the magnetization axis parallel to the sensor.  You want to realize the power of the magnetic subject at a ways farfar from the aspect of a disc/cylinder magnet, now no longer from the face.  Since our Magnet Calculator does not offer this data, and there isn't always an clean formula, approximate via way of means of multiplying the Calculator's solution via way of means of 0.5. 

UPDATE: Since this newsletter changed into posted, we have got delivered a brand new calculator which could estimate the sector power round disc/cylinder magnets each on and stale the critical axis.  While the above approximation remains valid, our Magnetic Field Calculator also can be used.

In our example, we are the usage of a Hamlin MDCG-four reed transfer, additionally to be had at DigiKey.  The spec sheet shows it'll set off in a variety among 12 to 38AT.  Assuming it's identical to twelve to 38 gauss, I plug a few numbers into the Magnet Calculator to discover the variety of distances I may count on a D42 magnet to set off this sensor from.  Since the sensor might be off to the aspect, I'm seeking out the calculator distance for double the ones numbers, or 24 and seventy six gauss.  For this magnet and sensor, count on it to set off someplace among 0.forty eight and 0.seventy four inches.