Potentiometers have long served as key components of electrical controls as well as position sensing. However, their size and expense make traditional potentiometers inappropriate for many applications, such as flat-screen touch input devices.
As the name suggests, “membrane” potentiometers are as ultra-thin as a membrane, able to measure less than a millimeter in thickness. They work largely the same as traditional potentiometers but can flexibly fit into a much wider array of more restricted applications – and often at lower cost.
But just what is a membrane potentiometer?
Like all potentiometers, membrane potentiometers are voltage dividers. They have two basic layers: (1) a resistive path printed onto a membrane base and (2) a collector with a printed short-circuit path. A circumferential spacer, usually constructed of sealant adhesive to seal the membrane potentiometer against environmental contaminants like dust or moisture, separates the two layers. When pressure is applied to the collector foil or membrane surface – with a wiper, finger, or magnet – the top and bottom circuits connect and create an analogue signal that is precisely proportional to the distance, angle, or position being measured.
This construction presents immediate differences from a traditional potentiometer, whose assembly is typically much more complex and much bulkier. However, the actual function and operation is nearly identical. Membrane potentiometers can be used as actual value transmitters in electrical control systems, as well as for position sensing.
Just how flat is a membrane potentiometer? Very flat!
Design can range between 0.5 mm (PET) and 2.1 mm (FR4-Magnet) for space restricted applications. For example, membrane potentiometers can be used as a ribbon controller with finger control in digital drums or pianos. They’re also very useful in robotics applications like controlling and monitoring the position of robotic arms, particularly where precision control and position sensing is critical.
The membrane layers can be constructed in a variety of ways. The membrane is commonly comprised of polyethylene terephthalate (PET), a moldable thermoplastic substance. Because PET can be molded at certain temperature thresholds, operation of PET-based membrane switches must be confined to certain temperature ranges – typically around -25°C to +55°C.
However, other materials and configurations are possible. For example, if contactless operation is desired, the base layer might be constructed out of PET, while the top collector incorporates a ferrite band. This contactless design can extend lifespan of the membrane potentiometer up to 20 million cycles. The variety and customizability of membrane potentiometers means they can be designed to fit almost any application perfectly.
Technical wordsmith and guest blogger for Hoffmann + Krippner.