It might appear that little has changed with potentiometer technology for years; this is untrue, especially with the emergence of the Spectra Symbol Membrane potentiometer from Variohm EuroSensor. The SoftPot and HotPot membrane potentiometers are principally based on a voltage divider construction. They can measure multiple of linear and rotary angles because the product is printed on a substrate; thus, any design can be achieved. Then precision cut to angle specification. The system is impervious to EM radiation and is sealed at IP66. The SoftPot is able to function up to +60 C, while the HotPot can function at +125 C. The HotPot opens the possibilities for many industrial and automotive applications because of the heat capabilities and the durability (>10M lifecycles, or >20M dithers).
Techniques
The construction is made by a printed element on a bottom layer, then a spacer mounted area around the element, followed by a top collector, by depressing the top layer to connect with the bottom element, will create a voltage divider signal. This construction prevents the scraping that occurs with a wiper potentiometer because the wiper is not directly in contact with the element, but is rolling or sliding on the top circuit layer.
Because of this construction, no debris, dirt or water can enter the conductive area; the spacer creates a sealed environment. When a regular potentiometer is sealed, it often will increase the torque and can be costly to set up. The force sensitivity for the traditional wiper is also avoided, as there is a range of forces that can successfully be applied to the membrane sensors.
The membrane potentiometer is just like a wiper potentiometer/conductive plastic, etc. in its basic form, except that it is sealed and uses a different wiper system.
The difference
The increased wiper force required for the membrane potentiometer ranges from 85 grams to 200 grams, which enhances the ability to withstand shock and vibration significantly. The traditional potentiometer has problems due to the light force, at 8 grams to 20 grams of the wiper force. Thus the membrane potentiometer has added a level of stability to the sensor system through its wiper construction.
Shaft less potentiometers are difficult to seal and have to balance radial and axial forces. Due to the membrane potentiometer construction, no shaft balancing is required, and the lower material requirements make the membrane pot more cost efficient.
Cost
Ultimately, one of the greatest drivers on the market is the cost. There is a significant cost improvement with the membrane potentiometer when comparing sensor-to-sensor, however, there is even more savings available when considering the application of the sensor. For example, instead of adding multiple fixtures to ensure the placement of a bulky potentiometer, the 0.5mm membrane potentiometer can fit into almost any design without compromising the construction of the system.