Rotary Potentiometers

For precise setpoint setting by hand

Guide for Rotary Potentiometers

Guide for Rotary Potentiometers

What is a rotary potentiometer?

This guide deals with potentiometers as input elements in the function as human-machine interface. For general information about potentiometers as actual value transmitters click here.  
With rotary potentiometers the electrical resistance of the potentiometer is changed by a rotary movement. Rotary potentiometers have a resistance element on which a wiper taps the voltage potential. Rotary potentiometers have three electrical connections for the electrical connection and a shaft for the mechanical coupling of the rotary knob. In terms of design, they can have some special features such as integrated end stops or a slipping clutch. The practical possibility of adapting the rotary inhibition of the shaft to the requirements of the application underlines their field of application as an interface between man and machine.

Series MCD17

Adaptation of the operating torque

Ball bearing with shaft

For a potentiometer shaft to rotate, a certain torque is required, the breakaway torque, to overcome the static friction. After overcoming the static friction, the actuating torque must be applied to maintain the movement. In practice, usually only the actuating torque is specified in the data sheet and the term "operating torque" is used in linguistic usage. The breakaway torque is negligible in most cases. 
The operating torque is determined at room temperature (around 20°C) and is given in Newton metres, for example 5 Nmm. This value is achieved by the interaction of several components. For example, by the type of shaft bearing and/or the use of sliding grease. In addition to other possibilities, these two components already allow a wide range of possibilities for matching the corresponding operating torque to the application. 
Special greases can be added which allow a requirement for a certain temperature range, prevent unintentional adjustment or make the haptic properties pleasant to the touch. The latter also has a considerable influence on the choice of the knob to be used. When using a large knob diameter, the user requires less force to generate the necessary torque due to the leverage effect. Therefore, a change of the standard value can offer advantages by adjusting the operating torque to the application. We would be pleased to support you in the selection and any necessary adjustments.

Mounting instructions for rotary potentiometer

Please follow the mounting instructions for panel mounting given in the data sheet, as well as the tightening torques and dimensions for threads and screws. Especially potentiometers with bushing can have a negative influence on the haptic if not mounted correctly. An intentional increase of the operating torque via mounting is not recommended. On the one hand, the inhibition cannot be ensured permanently and, on the other hand, it can influence the function of the rotary potentiometer.


Single or multiturn rotary potentiometer?

Knobs compared with one Euro

It depends on the respective application with which accuracy, reproducibility and speed an adjustment should be carried out. You can cover a maximum of 360° with a single-turn rotary potentiometer and 3600° with a 10-turn rotary potentiometer.
Example: You require a resolution of approx. 5° per adjustment step for your application and would like to implement this with a single-turn rotary potentiometer with 350°. 
In practice, it depends on how large you dimension the control knob and how fast or how large the path for an adjustment may be. With a relatively small knob, safe and precise operation by hand is difficult to achieve in our example. You would have to be able to set about 70 positions on one turn with the smallest of movements. A relatively large control knob would be better suited in this case to ensure comfortable operation. 
A multiturn rotary potentiometer could be more suitable for this example under the premise of a small control knob. A multiturn with, for example, 3600° offers considerably more comfort in handling for safe, exact and reproducible operation. However, further adjustment travels or several revolutions are required to set a required value. If quick adjustment by hand is required, a single-turn potentiometer has an advantage over a multiturn potentiometer.
In summary, the following can be stated: A single-turn is better suited for quick and coarse adjustments than a multiturn rotary potentiometer. With the latter, operating concepts can be realized that are much more finely graduated and precise, while at the same time requiring reproducibility. In addition, the choice of control knob has a decisive influence on the convenient adjustment options in practice.

General tips about rotary potentiometers

Normally, rotary potentiometers are integrated into a housing by means of panel mounting. We recommend using seals between the components if cleaning agents are used or if the application is in outdoor use. We recommend an additional shaft seal if the application is used at low temperatures. Otherwise, condensation can form on the resistor element and thus influence the signal. If further protection is required, potentiometers with sealed housings are available.

Particularly in battery-powered, mobile handheld applications, rotary potentiometers show their strengths in terms of power consumption. Only minimal power values are required for operation. This technology is therefore virtually unrivalled for applications requiring low power consumption.  

Our potentiometers provide almost exclusively a linear output signal. Exceptions are our sine/cosine potentiometers. Both are not suitable for audio applications as they do not have a logarithmic curve!

Completely pre-assembled sets

Our pre-assembled sets offer the advantage that the rotary potentiometer and rotary knob are matched to each other. The dimensions of the potentiometer shaft fit exactly into the mechanics of the rotary knob, the torque is matched to the behaviour of the rotary knob and a rubber sealing washer provides optimum protection for panel mounting. The rotary knobs have a 3-digit roller for presetting or reading the set points and the potentiometers are available in 3, 5 or 10 turn versions. For electrical integration, the pre-assembled combinations of rotary potentiometer and rotary knob are available with terminal connection or solder lugs.

Suitable rotary knobs for rotary potentiometers

Especially, the shaft geometry of the rotary potentiometer is decisive for the mounting of the rotary knob. Please ensure that the shaft is dimensioned appropriately and take the panel thickness into account. Our rotary knobs are designed for various shaft geometries. We would be pleased to support you in the selection process and accompany you during any adjustment process.

Our knobs

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Rotary potentiometers can be "operated" manually by hand. They are used as man-machine interfaces for the precise presetting of setpoints. For practical use, the operating elements have mechanically integrated end stops that limit a rotary movement and prevent it from crossing the resistance track. An optionally integrated slipping clutch protects the end stops from excessive stress.

Environmental requirements dictate the type of operation and often require product optimization. Of particular importance is the possibility of adapting the operating torque to the corresponding application requirements, for example to prevent unintentional adjustment. In addition, the haptic properties can be influenced to a desired degree.

MEGATRON is your partner for corresponding product optimization. Within the scope of our consultation, we define, together with you, the optimal product for your "design in". Our claim is to provide each customer individually with the best functional and economical result. With high delivery reliability and assured quality products, we focus on long-term partnerships and accompany you throughout the entire lifespan of your application.

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