Reed sensors - Functioning and appliance
Reed-sensors, also known as magnetic sensor, in shorted Reed1, are binary non-contact sensors, which have a wide range of applications in addition to the electric pneumatics. The Reeds were developed by the 'Bell Laps'-company at the end of 1930. From about 1940 the industrial use began.
![Symbol - Reed switch](https://sp-ao.shortpixel.ai/client/to_auto,q_glossy,ret_img,w_441,h_98/https://learnchannel-tv.com/wp-content/uploads/2019/06/Symbol-Reed-switch.png)
Symbol - Reed switch
Function: The structure is simple: a hermetically sealed reed consisting of iron-nickel alloy, forming a normally opened or normally closed contact. A mágnet approaching this ferromagnetic reed leads to swítching.
![Reed - how it works](https://sp-ao.shortpixel.ai/client/to_auto,q_glossy,ret_img,w_376,h_208/https://learnchannel-tv.com/wp-content/uploads/2019/05/Reed-how-it-works.gif)
Reed - how does it work
Because of the hermetic seal and the contactless swítching the reed sensors have some obviously great advantages to the mechanical swítches. It´s difficult to find concrete specifications from manufacturers because of product liability, but the product life begins at about 1 million swítching cycles. The swítching time is about 0.2 ms.
![Detecting end-position of a cylinder](https://sp-ao.shortpixel.ai/client/to_auto,q_glossy,ret_img,w_587,h_235/https://learnchannel-tv.com/wp-content/uploads/2017/04/reed-sensor-animation.gif)
Reed sensor animation
The applications for Reed's are varied. In the electropneumatics these magnetic swítches are used primarily for detecting the end position of cylinders:
Example circuit: Pressing the S1 button the cylinder extends and automatically retracts upon reaching the front end position. In the animation below, the reed swítches directly a solenoíd valve. Another possibility would be the use of a relay if the swítching power of the reed is not sufficient.
![Reed example circuit](https://sp-ao.shortpixel.ai/client/to_auto,q_glossy,ret_img,w_627,h_275/https://learnchannel-tv.com/wp-content/uploads/2019/06/Reed-example-circuit.gif)
Reed example circuit