Position sensors are considered to be a large family with many different types of sensors, however each sensor in this family is unique with respect to the principle on which it works and its construction. So is the case with potentiometric position sensors, which are considered to be the most inexpensive of all position sensors.
One important thing that I would like to clarify first is that, we are not talking about ‘potentiometric sensors’. Potentiometric sensors are used to measure the electrical potential of an electrode while no current is flowing through it. They are a type of chemical sensor.
On the other hand, the star of this story is the potentiometric position sensor, which is used to measure the rotary or linear displacement or position of an object using the technology developed for potential military applications which then were adapted to industrial segments. They are also referred to as “Potentiometers”. Some of these require physical contact with the moving targets whereas there are other types of potentiometers that are non-contact types, use the Hall effect IC technology and have long life as compared to the latter ones. One can refer a potentiometer as a normal circuit where the resistance can be changed manually with the help of sliding contacts.
It becomes very important to understand the classification of the product we are going to purchase, as this would help us narrow down our search. There are many different ways to classify Potentiometers. The broader categorization is based on their function or the area of application:
- Angle Sensor: These are usually round, rotary sensor used to measure the angular displacement of the body it is in contact with. They are also referred to as rotary potentiometers.
- Linear Sensor: These are found in different shapes and sizes which does not affect the linear displacement of the body it measures.
Another way to classify them is based on the materials they are made of:
Wire wound potentiometers: These types of potentiometers are made by winding several rounds of wire around the shaft of a material that is non-conducting. An adhesive is used to bond the turns of the coil together. Now when body to which this is in contact with moves, the slider moves on the track of the potentiometer and makes contact with successive turns of the coil. It is considered that larger the number of turns of the coil, better is the coil resolution. Mathematically resolution is inversely proportional to the number of turns, so lower the value of resolution, the better it is. The wire wound potentiometers have low noise and are considered to be rough and tough mechanically.
- Carbon film potentiometers: They are made by depositing carbon composed ink on an insulating body. The insulating body in most of the cases is phenolicresin, which is one of the most commonly used materials for potentiometers. These are cheap and are better in resolution than the wire wound potentiometers. They have reasonable life and tolerable noise levels.
- Plastic film potentiometers: These potentiometers are made of specially saturated plastic material with resistance characteristics that can be controlled properly. These are used for both rotary as well as translational slider movements. They have better resolution than the wire wound potentiometers, can be used for a longer period of time without much wear and tear and produce low noise.
Then we can also classify them based on their design structure.