How it works
How the membrane potentiometer works: Easy to understand, Simple to use
Spectra Symbol membrane potentiometers have two main functions: 1) Sensor or 2) Set-Point device. Application dictates function 1 or 2.
What is a Membrane Potentiometer
In basic terms, potentiometers are resistive elements or conductive plastic proximity sensors/transducer sensors with a sealed encasement and simple wiper assembly.
The wiper is a non-conductive part that connects the top and bottom circuit as the wiper actuates the potentiometer from the outside of the element. The membrane potentiometer is a three-wire system: a layer of material with two resistance output channels and the other layer serves as the electrical wiper.
Design and Construction
The membrane potentiometer is made of materials ranging from polyester to fiberglass. This potentiometer also functions as a voltage divider. By pressing the wiper down on the top circuit to close the connection with the bottom circuit, the linear transducer produces the desired electrical output. The membrane potentiometer can also be actuated through manual (hand) control. The top and bottom circuit are separated by 0.127mm of spacer adhesive build-up. The contact occurs by pressure from the wiper on the top circuit, which pushes down until the top circuit connects with the bottom circuit to create a potentiometric output. Spectra Symbol provides membrane potentiometers for multiple applications. The temperature ranges allow for applications across the board, from -45 C to 85 C. Additionally, the life cycle limit is beyond 10 million cycles. The construction of the wiper design can adapt to any application because most materials can serve as the wiper: plastics, metals, sliders, rollers, wheels, etc. Anything with a rounded edge can connect the top and bottom circuit together, as demonstrated in the drawing located to left of this paragraph:
Wiper design
The construction of the wiper design allows for a constantly "open" circuit until the wiper connects the top and bottom circuit. Typical wiper materials are delrin, plastic injection molded products, metal rollers with back-loaded springs, sliders attached to lead-screws, etc
Electrical Output
As shown in the above drawing, until the wiper pushes the top circuit down to connect with the bottom circuit, the circuit is “open” (not giving output). Once a wiper depresses the membrane potentiometer top circuit, the output is continuous, giving absolute position.
Tolerances:
• Total Resistance is the resistance reading from one side of the carbon element to the other. Our standard is ±20%.
• Linearity is discussed in terms of independent linearity and the variance is determined in reference to the average position; standard is ±3%.
• Resolution, meaning the smallest increment of movement, is infinite and will produce varying output to the degree of width of the contact wiper.
The interactive picture to the left shows the theoretical output of a potentiometer in motion.
