Cylinder Sensor Switch

Cylinder switch or cylinder sensor is a kind of switch that confirms the position of the cylinder piston by sensing the magnetism of the magnetic parts on the piston, so as to make related actions: turn on the power, or turn off the power, or send out an electrical signal.

Cylinder switches are normally installed at the ends of travel of the cylinder to signal that a particular motion is complete. These signals usually feedback to a PLC (or other controller) and are used to provide cylinder position indication, cycle count, or to confirm operation. Sometimes, it’s used to control the solenoid valve which connected with the cylinder.  It is also possible to use cylinder switches mid-stroke for more sophisticated operations.

How does it work?

There are usually two types of cylinder switches on the market, one is a reed switch and the other is a magneto resistive switch which is also called as Cylinder Magnetic Sensor.

The cylinder switch is fixed on the outer wall of the cylinder barrel. When the piston equipped with the magnetic ring runs to the position where the magnetic switch is installed, the switch induct the change of the magnetic field and an electric signal is generated. This electric signal is transmitted to the PLC, or simply turns on or off the power of the solenoid valve to control the operation of the cylinder.

Types

Reed Switch

Reed switch is the abbreviation of dry reed switch. It is a passive electronic switching element with contacts. It has the advantages of simple structure, small size and easy control. Its shell is generally a sealed glass tube with assembled two iron elastic reed plates and filled with inert gas. Usually, the two reeds made of special materials are separated.

Magnetic Switch

It is a kind of induction switch that uses GMR (Giant Magneto resistive) or AMR (Anisotropic Magneto resistive) technology to sense the change of the magnetic field, and through a assembled transistor to generate an electrical signal.
GMR (Giant Magnetoresistive) and AMR (Anisotropic Magneto resistive) two solid state magnetic sensing technologies, both consist of layers of ferromagnetic material that changing in electrical resistance when exposed to an external magnetic field. AMR based switches have a higher sensitivity and narrower sensing field compared to less expensive GMR based switches. AMR switches are a better choice for cylinders with short strokes.

The Difference 

1.Durability:
Reed Switch: The nominal life of the reed switch is 5 million times. However, according to the different load conditions, the life value will deviate.

Magnetic Sensor Switch: since there is no mechanical contact inside the contactless magnetic switch, the life is semi-permanent.

Note: Semi-permanent does not mean that there is no life limit.
2. Oscillation phenomenon:
Reed Swithc: the springing of the reed contact will cause the output signal to oscillate when opening and closing
Magnetic Sensor Switch: Since a transistor is used for ON/OFF action, it will not cause the output signal to oscillate.
3. Switching current:
Reed switch: Due to the limitation of the current that can flow through the reed contact, it cannot be opened and closed with large current.
Magnetic Sensor Switch : Although the heat release based on the triode has a certain limit, it is still larger than the maximium capacity of the contact magnetic switch. In addition, there is a certain margin redundancy space for instantaneous changes (such as inrush current, etc.).
4. Sensitivity to magnetic fields: Sensor switch are more sensitive than reed switches, and operate reliably even with weak magnetic fields

5.Longevity:Magnetic sensors are insensitive to long term effects of magnetic fields, reed switches can become permanently magnetized over time.

6.Response time:Reed switches have a slower response time than electronic switches, resulting in lower switch accuracy.

7.The reed switch is restricted by working conditions. When it is turned on, the switch produces a certain voltage drop, and when it is turned off, there is a certain residual current flowing through it. It should be considered when selecting it. Although the sensor switch has an extra wire, it is not troubled by unfavorable factors such as residual current and works more reliably.