These sensors are available :
- in length from 50 to 500 mm for the linear version
- into 90°, 180°, 270°, 345° and 360° for the rotary version
They are deliverable in the form of :
- element alone, the user who can use a moving part of its mechanism like cursor,
- in kit form (element plus cursor) to integrate
- like the traditional position encoders.
The potentiometers are components which are familiar for us and which we meet for example in the radio stations and the stereo chains. When the button is turned or we push the cursor, we can for example set the sound volume.
What occurs from a technical point of view?
An electric tension is applied between the entry (position zero) and the exit (maximum position) of a resistance and a part of this signal proportional to the position of the button compared to the total travel is taken.
This principle is also applicable to the Sensofoil sensors.
When somebody applies a pressure to a given position of the sensor, this one directly provides a signal proportional to the input signal function of the relative position of support compared to the total travel. But contrary to the traditional potentiometers, if no pressure is applied, no output signal is available.
Another difference is that it is possible to apply a simultaneous pressure in several places of the track. In this case, electronics can easily calculate the distance separating the two points from extreme contact.
This characteristic can easily be exploited in many applications such as for example in the industry of clothing. Let us imagine that one must measure at exit of chains the length of trousers, it is enough to pose this one on a table equipped with Sensofoil and to press at the same time on the belt and the bottom of clothing. It does not remain any more with electronics but to calculate the distance between the two points.
There already exists on the market a multitude of potentiometers which are universally used in many applications but their employment often requires to take particular precautions according to the environment.
The Sensofoil sensors consist of several superimposed layers of polyester, stuck between them by means of an adhesive acrylate which ensures a perfect sealing with respect to outside. This construction makes it possible to obtain without difficulty an index of protection IP65 and makes the track insensitive with the stains and moisture.
The lifespan of the traditional potentiometers is limited. The cursor often called wiper bears its name well. Indeed, it in general consists of an elastic metal part which rubs on the resistive element and, to the wire of displacement, one, the other or both wear. Of course, the choice of adapted materials and a geometry makes it possible to push back the limits of lifespan, but... Sensofoil - they need only one reduced force (about 0,5 to 1,5 Newton) exerted orthogonally with the track and on the outside of the sensor. The latter consists of an elastic sheet polyester which becomes deformed temporarily (about 0,2 mm) without transmitting movement of wear to the resistive element located on the internal face. The element being used as cursor needs to be electrically conductive (more noble metals...); the POM (Delrin) for example is appropriate perfectly in such an application and allows an quasi-unlimited operation without wear neither of the cursor nor of the sheet polyester.
The traditional potentiometers are relatively cumbersome.Sensofoil are :
- Extra-flat, their thickness not exceeding a millimetre,
- Easy to fix thanks to their self-adhesive face,
- Do not require a cumbersome moving element, the cursor can form integral part of the machine