Littelfuse Introduces The World’s Smallest Reed Switch

Littelfuse has a nearly 100-year history of being a leader in the manufacturing of fuses, fuse holders, and circuit protection equipment for the industrial electrical field. Their catalog of success doesn’t just stop at fuses, though. They also have product lines consisting of diode arrays, protection relays, solenoids, battery management, and many other components for the electronics industry. Thinking small, Littelfuse's recently introduced 59155 and the 59156 reed switches are claimed to be the world's smallest.

 

Littelfuse’s tiny reed switch for position sensing. Image used courtesy of Littelfuse

 

What is a Reed Switch?

When you need to detect the position or presence of components, a reed switch is a great tool. This kind of sensor consists of a single contact that is influenced, and a contact set closed, by a passing magnetic field nearby.

Typical applications of reed switches include detecting the forward or retracted position of a pneumatic cylinder. As the piston head moves past the reed switch, the contacts close, allowing current to flow through the switch.

Reed switches are also commonly used in security systems to detect the position of a door or window. A magnet is affixed to the door or window and the reed switch is fixed to the door or window frame. As the door or window is closed, the magnetic field pulls the contact closed, signaling to the security system that the windows and doors are closed.

Most reed switches are flange mounted to flat surfaces, while others are designed to fit in specifically engineered slots on actuators or door enclosures.

 

Close-up view of the working element inside a reed switch sensor package. Image used courtesy of Wikimedia

 

Littelfuse Reed Switch 59155 / 59156

Some reed switches that are used in industry are large and bulky to allow large amounts of current through the contact, others are smaller as they only need to relay a low-current signal to a control system to indicate that something is present.

Littelfuse has announced the 59155 and the 59156, claiming the sensors are the smallest reed switch on the market today. Smaller switches allow designers and engineers to place sensors in previously impossible situations or simply reduce the overall footprint of a design. Both the 59155 and the 59156 measure 12.7x9x3 mm and are capable of switching 120 volts AC or 170 volts DC at 10 watts.

 

Pneumatic and electric actuators are common applications for reed sensors. Image used courtesy of Wikimedia

 

The case contains a flange for mounting to surfaces with an M2 screw. The difference between the two switches is a mirror-image flip in which way the flange is facing, with the 59155 flange facing down, so the wires exit the switch to the right, and the 59156 flange faces up, with the wires exiting to the right.

Both models are available with 6 to 10 ampere-turns or 10 to 15 ampere-turns (a measure of the sensor’s sensitivity) and a normally closed or normally open contact model. Both models also have an operating time of 0.5 ms and a release time of 0.2 ms, they can also operate in temperatures of -40°C to 105°C. The 59155 and the 59156 can both switch up to 0.25 amps with DC voltage or 0.18 amps on AC voltage, easily sufficient for any normal controller I/O configuration.

All of the variations are single pole / single throw, which means there is one connection on each side of the switch allowing the control of only one simple circuit.

 

Sensing for Industrial Automation

In the world of automation, feedback is absolutely important. In the case of actuators and enclosures, we could rely on contact limit switches or simply allow the device to open and close with a hard stop at its extreme limits. But in order to truly create a long-lasting control system, sensors such as Littelfuses’ new reed switch, are a critical component of the modern control system.