- Cylinder sensors
- Technology
Technology
ifm offers sensors with
AMR technology
The AMR cell consists of a very thin layer of MU metal (perm alloy).
The nickel-iron alloy layer has a thickness of e.g. 20 nm. When this layer is influenced by a magnetic field, its electrical resistance will change (similar to the GMR cell). The AMR technology enables a narrow detection range and a small hysteresis. Therefore, this technology is very well suited for short-stroke cylinders or for high-precision applications.
GMR technology
A GMR cell consists of three layers of material. Two of these layers consist of cobalt (magnetisable) and one layer of copper (non-magnetisable).The electrical resistance of these layers depends on their magnetisation.
The electrical resistance can therefore be changed by applying an external magnetic field. This influence on the electrical resistance can be detected and thus causes the sensor to switch.
GMR technology is very reliable.
In unfavourable cases, however, multiple switching points are possible. This can happen if strong permanent magnets are installed in the cylinder. The detection range (the range in which the sensor switches through the magnet) is very wide and the hysteresis is also large.
Reed technology
A reed switch consists of two overlapping metallic contact plates. When no magnetic field is acting on them, the switching contacts are in the idle state. This means that the circuit is open in the normal state and no current can flow. As soon as the field of a magnet exceeds a certain strength, the contact plates will close. This allows current to flow. If the magnetic field weakens again, the plates will open and the switch will be in the idle state again.
These plates are located in a glass tube.
Comparison of AMR, GMR and mechanical reed sensors
| AMR | GMR | Reed | |
|---|---|---|---|
 |
 |
 |
|
| Type | Semiconductor output | Semiconductor output | Mechanical reed contact |
| Life | Unlimited cycles | Unlimited cycles | 1 to 2 million cycles |
| Repeatability |  |
|
 |
| Response time | |
|
|
| Sensitivity | |
 |
|
| Temperature stability | |
|
|
| Reaction to strong magnetic fields | |
Several switching points are possible | Several switching points are possible |
| Short-stroke cylinder suitability | |
 |
|
| Sensitivity to piston vibration |
|
|
|