Why use the cover foil?

What are the advantages and disadvantages of using the cover foil?

Advantages

The cover foil can be used to protect the magnetic scale in applications where it could be subject to physical change. If a hot particle strikes the magnetic scale, it could burn the rubber and disrupt the magnetisation which would lead to incorrect readings. Sharp objects can also damage the scale by scratching it and thereby disrupting the magnetisation.

The cover foil is also easy to clean. So for applications that require regular cleaning of the scale surface to avoid excessive dirt build up between the scale and readhead it is advisable to use the cover foil.

Disadvantages

The main disadvantage is that the cover foil and the magnetic scale have to be installed separately doubling the installation time.

Also, the cover foil cannot be re-installed to the magnetic scale. Removal of the cover foil after installation will damage the rubber strip.

Once the cover foil is applied, the batch ID of the scale is also hidden below the cover foil.

The cover foil decreases the ride height by 0.1 mm.

Why is the cover foil not as wide as the scale?

The cover foil is about 0.5 mm thinner to allow for installation tolerances. Also for safety the cover foil should never overhang the edge of the magnetic scale.