Hollow Shaft Potentiometer

Fields of application for potentiometers
Potentiometer are long-established sensors. They are popular because it is easy to integrate them into the application, the power consumption is low, the signal is available immediately without computing times and, above all, they have proven themselves over a long period of time, and their mode of operation is well known. Basically, potentiometers are used wherever angles or positions need to be measured. The multitude of potentiometer types and their variants cover a very broad application landscape. The differences between the potentiometers are already apparent within the respective potentiometer technology. It therefore always depends on the respective application whether the potentiometer is suitable for the intended task. In general, potentiometers are not suitable for high mechanical shock loads and not for high speeds > 400 rpm but are considered resistant to EMC influences and insensitive to ESD influences because they are passive components.

What is a potentiometer?
The potentiometer was invented by Johann Christian Poggendorff in 1841. It has been used as an input element and sensor since the beginning of commercial use in electrical engineering. In principle, the design and function of all potentiometers are the same. They have a so-called resistance element with a movable wiper contact, which taps a voltage potential on a resistance track. Potentiometers are therefore variable voltage dividers. The resistive element is circular for rotary potentiometers and linear for slide potentiometers. For connection to the application, rotary potentiometers have a mechanical connection (usually a shaft) and electrical connections (usually three).

Electrical connection and signal output of potentiometers
Potentiometers usually have three connections: Two for the resistive element and one for the wiper (signal output). If one follows a usual connection diagram for a potentiometer and applies 0 V to the defined connection "one", 5 V to connection "three" and turns the shaft of the potentiometer, the voltage signal from 0 to 5 volts is "output" via connection "two" (on the wiper). An absolute analog signal is available immediately without switch-on delay and calculation times. The value of the signal output depends on the applied voltage in relation to the position of the slider on the resistance track. By changing the position by means of rotational movement and direction of rotation, a voltage difference between position A and position B can be detected and thus the position can be determined in angular degrees. Our potentiometers almost exclusively provide a linear output signal. Exceptions are our sine/cosine potentiometers.

Potentiometer technologies
Our precision potentiometers are available in three different resistance elements (technologies). The respective resistance element is decisively responsible for quality and function in the application. Wirewound potentiometers have a resistor track made of wire, which is usually wound around a ceramic, conductive plastic potentiometers have a resistor track made of conductive plastic, and the hybrid potentiometers have a resistor track made of a combination of wire and conductive plastic.

Wirewound potentiometer
In principle, they can also be used as a variable resistor (in so-called rheostat circuit). Nevertheless, we recommend the voltage divider circuit, since the components were designed for this purpose. They are available in so-called single turn (< 360°) and multiturn (> 7200°) versions. They have a limited-service life due to abrasion and due to the winding jumps of the wire windings "steps" in the output signal, which manifest themselves as noise when the slider moves.

Conductive plastic and hybrid potentiometers.
Both technologies must never be used as variable resistors (rheostat circuit), but only in the voltage divider circuit. Conductive plastic is only available as single turn and hybrid only as multiturn variants. Hybrid potentiometers make it possible to use the advantages of conductive plastic potentiometers also in multiturn potentiometers. They have a significantly longer lifespan because the resistance track is very smooth. They also have a theoretically infinite resolution, a particularly smooth output signal, superior linearity and allow higher adjustment speeds.

Multiganged/Tandem Potentiometer
If redundancy of sensor technology is required in applications, so-called multiganged potentiometers or tandem potentiometers in double version are often used. The field of application ranges from mechanical engineering to aviation. For the tight linearity tolerances of the potentiometers to maintain their quality, it is important to ensure that the heat generated during operation, due to the stringed construction, does not have a negative effect on the properties of the potentiometer.  It is therefore necessary to reduce the nominal load according to the table.

Oil-filled potentiometers
Oil-filled potentiometers are typically used in special application environments where, for example, aggressive gases, harmful salts or moisture can be a problem. These potentiometers are also characterized by the fact that the wiper contact resistance is particularly stable over the entire lifetime, as the oil filling suppresses corrosion on the wiper or near the. Some applications of these potentiometers include control systems in areas such as shipbuilding, coastal electrical installations, mines and pits, ironworks, chemical plants, and machine tools. Some applications, however, require additional approvals, such as explosion protection, which must be obtained separately for each application.

Measuring amplifier/signal converter for potentiometers
As passive components, potentiometers do not offer standardized output levels such as 0..10 V, 4..20 mA. Please note that the output signal of the potentiometers should be tapped by means of a voltage divider circuit and thus virtually no current flows via the output. Using the signal itself as a voltage or current source for a converter is therefore not necessary. In order to nevertheless generate standardized signals in a simple design, we offer measuring amplifiers that allow standardized signals to be obtained by means of an external voltage supply.

IP protection class
Almost all our potentiometers are specified with protection class IP40 and almost all of them can be increased to protection class IP65 with a shaft sealing ring on the shaft side. If a degree of protection is required, e.g. for the housing, the MFP500 and AL17IP series as well as the oil-filled OFH, OF5001, OF30, OF50 series meet this requirement. For numerous potentiometer series there are options that allow a sealed housing.

Shaft torque
Our potentiometers are offered with precision ball bearings or sleeve bearings. In general, potentiometers with precision ball bearings have a lower torque than potentiometers with sleeve bearings. Servo flanged potentiometers are in principle always equipped with ball bearings. For almost all potentiometers it is possible to change the operating torque (e.g. 2 to 3 Ncm at room temperature). In addition to the pleasant haptic properties, an increased rotational resistance prevents unintentional adjustment due to vibrations of the machine. A wide selection of pre-assembled sets and adjustment knobs are available for your application.

Mechanical stops & slipping clutch
Mechanical stop or without stop  
Mostly the mechanical end stop is used for applications for manual setpoint setting. Please note the max. permissible stop torque and that all multiturn potentiometers have a mechanical end stop. For potentiometers without a mechanical stop, a voltage fluctuation occurs when the ends are over-turned. Do not use the output signals of this end range as useful signals.
Slipping clutch
Slipping clutches are used with our multiturn potentiometers. The main purpose of the slipping clutch is to protect the mechanical stop from damage. However, if the clutch is subjected to permanent stress, it may wear out more quickly and its lifespan will be shortened. Please take this effect into account.

Adjustment, mounting types and soldering instructions
Zero point adjustment
The zero point adjustment can be made conveniently with a screwdriver slot on the shaft. The possibility to integrate a screwdriver slot on the shaft exists for all series with shaft and is already implemented as standard for some of them. For potentiometers with servo flange, zero adjustment is possible by simply turning the potentiometer housing. For this purpose, the synchro clamps must be loosened beforehand.
Soldering note
For soldering the connections, soldering irons with max. 60 W may be used (< 350 °C) and contact may be applied for a maximum of three seconds.
Installation types
For panel mounting, the potentiometer with shaft must be mounted in a precisely fitting hole without play. For potentiometers with a fixing pin, the so-called anti-rotation pin, please include a corresponding drill hole. For hollow shaft potentiometers, rigid fixing of the housing must be avoided. This is because the hollow shaft is not suitable for taking over the bearing function of the actuating shaft. The specifications in the data sheet for housing depth as well as housing diameter do not consider the dimensions of the electrical connections. In the case of limited installation space, please consider above all the alignment of the connections and the additional space required for these.

Hysteresis / Backlash
When the wiper passes over the resistor path in one direction, a certain electrical value (U1) is reached at a certain point (α1). If the wiper is moved in the opposite direction, the same electrical value is reached at a different location (at a different angle, α2). This difference is expressed in angular degrees and is called hysteresis or backlash. Hysteresis thus describes certain effects on the accuracy of the measurements. Due to this effect, the output signal can be assigned to two different angle values, which depend on the wiper direction.

Linearity
The linearity expresses the deviation of the output voltage curve from the theoretical, ideal curve. Usually, independent linearity is specified for potentiometers, which does not require the straight line to pass through the zero point. To determine this, an optimal straight line is drawn through the actual output voltage curve so that the deviations of the curve from the straight line are minimized.   The lower the linearity value, the smaller deviations from the correct measured value can be expected.

Product customizations and options
For over 60 years, MEGATRON has been a reliable partner for your design-in needs. In addition to the wide range of options available for our sensors, we offer specific designs that meet your exact application requirements, even for small quantities. Whether it is a prototype project or series production - we are happy to support you.