A potentiometer sensor is an electromechanical component that consists of a resistor where the voltage divider value can be measured at any position by means of sliding contacts between the applied voltage values. Physically, a potentiometer consists, at a minimum, of a resistance track, a collector track, and a sliding contact that can be moved along the resistance track by means of mechanics (Figure 1). The movement of the sliding contact can be rotatory (angle) or translational (path).
The available types of potentiometers vary in the type of material used for the resistance track. Today, the three most commonly found materials are carbon and cermet, wire-wound, and conductive ink. In the case of carbon and cermet, a chemical mixture of conductive elements consisting of carbon (carbon = air-drying varnish filled with carbon black) or cermet (ceramic-metal) are applied to a simple, basic carrier such as laminated paper (FR3 or with cermet, in some cases also ceramic) in silk-screen printing. The lifetime is very short — just several hundred movements for carbon. In comparison, cermet lasts much longer — up to 50,000 movements.
In wire-wound potentiometers, fine resistance wire is evenly wound on a basic carrier such as insulated copper wire. In the early days of potentiometer sensor technology, wire-wound potentiometers were often utilized as big and chunky regulating resistors. In the 1960s, the use of fine wire potentiometers became much more common as performance and lifetime improved. Modern wire-wound potentiometers provide very good linearity values (0.1% in the voltage divider mode) and a service life of 1 million cycles. Specialized companies have consistently expanded the development of this technology, and are still using it for research and development, or for small quantities with special qualities.
At the end of the 1960s with the development of high-strength plastics, carbon black sensor components were integrated with a matrix of thermosetting resins. At the beginning of 1980, the German automotive supplier VDO introduced conductive plastic potentiometers to the market for use as an electronic gas pedal.
Starting in approximately 1982, manufacturers developed a technology to print the conductive plastic directly upon a variety of circuit board materials. FR4 (woven glass and epoxy) is the most common, as well as FR2 (phenolic cotton paper), CEM-1 (cotton paper and epoxy), CEM-3 (nonwoven glass and epoxy), and FR6 (matte glass and polyester). Other suitable circuit board materials include FR1 to FR6, CEM-1 to CEM-5, and G10 (another woven glass with epoxy).
This breakthrough of conductive plastic technology can be used in a wide variety of applications such as accelerator pedals and seat memory function for automobiles, door memory function for hospitals or public buildings, as well as smoke vent status detection, controlled tracking of solar panels, position adjustment of wind turbines, and general machine control. With the increased lifecycle compared to wire-wound potentiometers, membrane potentiometers are also useful for industrial machine and system controls, as the lifetime for potentiometers with conductive plastic is 10 to 20 times higher than that of wirewound potentiometers.
This technology is now the first choice for high-grade mass products that require long life and accuracy. In the best case, the accuracy of conductive plastic potentiometers can be linearized up to 0.05%. The operating lifecycles can far exceed 10 million cycles, and are often limited only by their associated mechanical parts.
Printed potentiometers made of polymer pastes can be an integral component of the circuit board for a range of modules and devices. To save space and reduce costs, the potentiometers can be printed directly on the substrate; for example, PCB material such as FR4.
A unique, innovative technology enables durable polymer paste (conductive plastic) to be printed on flexible foil. With these printed potentiometers, the voltage dividers/voltage values are taken directly by means of a wiper, which is a metal slider (scraper) that creates a contact between the conductive paths on the foil (Figure 2).