Měření natočení a ovládání zařízení

Pro výběr správného průmyslového potenciometru je nutné specifikovat základní parametry:

  • Mechanický úhel – jedno-otáčkové s dorazem (standardně 270 nebo 320°) nebo bez dorazu (360°), více-otáčkové (počet otáček)
  • Elektrický úhel [°]
  • Elektrická zatížitelnost [W]
  • Mechanické upevnění (centrální závit nebo servo)
  • Hodnota odporu [Ohm], tolerance odporu a linearity [%]
  • Životnost [ot]
  • Krytí

Průmyslové potenciometry se používají hlavně jako úhlové snímače polohy a někdy také jako nastavovací prvky, např. pro regulaci v automatizaci. Vyrábějí se také v provedení jako víceotáčkové drátové potenciometry nebo tandemové potenciometry. Jsou historicky nejstarší, ale v řadě aplikací stále populární, hlavně kvůli nízké ceně. Největší výhodou potenciometrů je to, že nepotřebují pro svůj provoz žádnou energii, je to pasivní snímač. Používají se hlavně jako snímače polohy a někdy také jako nastavovací prvky, např. pro regulaci. Pro vyšší zátěž se používá technologie vinutého drátu. Pro nižší zátěž je vhodnější technologie s plastovou dráhou, která je mnohem trvanlivější a má vyšší rozlišení. Výsledkem je plynulejší chod a mnohem delší životnost v řádu až několika milionů pohybů. Specializujeme se i na zakázková provedení, kde lze např. definovat max. úhel otočení, průměr hřídele, utěsnění proti vlhkosti atd.

 

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Průvodce potenciometry

Potentiometers field of application

Potentiometers are long-established sensors. They are popular because of
  • their easy integration into the application,
  • their power consumption is low,
  • and the signal is immediately available without computing time.
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 large number of potentiometer types and their variants cover a very broad application landscape. Even within one particular potentiometer technology the variety of properties and options is broad. It therefore always depends on the respective application whether the potentiometer is suitable for the intended task.
As a general rule, potentiometers
  • are not suitable for high mechanical shock loads
  • nor for high adjustment speeds >400 rpm, but are considered
  • insensitive 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 the 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 of rotary potentiometers is circular and for slide potentiometers linear. 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 resistance 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 the connection "three" and turns the shaft of the potentiometer, a voltage signal of 0 to 5 V is "output" via connection "two" (on the wiper). An absolute analogue signal is immediately available without any switch-on delay and computing times. The value of the signal output depends on the applied voltage in relation to the position of the wiper on the resistance track. By changing the position by means of a 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 provide almost exclusively a linear output signal. Exceptions are our sine/cosine potentiometers.
The angular position of rotary potentiometers can be easily determined using the formula below: θ=VoutVinelectrically effective angle of rotationθ=VoutVin∗electrically effective angle of rotation Example: θ=45320°272°θ=45∗320°≈272° If approx. 4 V is measured at the wiper with a total angle of 0° to 340° and a voltage range of 0 to 5 V, this would correspond to an angle of approx. 272°. However, this is a theoretical value, since potentiometers have different values for hysteresis and linearity tolerance depending on their design.

How many contacts does a potentiometer have?

Does a potentiometer have two, three or more connections?

This question can only ever be answered on the basis of the respective potentiometer variant. In most cases potentiometers have three connections or contacts. However, if several potentiometers are constructed in a row in one housing, the number of contacts increases. For example, a tandem potentiometer (2 x potentiometer constructed in row) then has six connections / contacts. If the application requires a centre tap for the potentiometer, the number of connections / contacts increases accordingly, usually from three to four. Non-linear potentiometers (sine / cosine) on the other hand have five connections: One connection for positive and one for negative voltage (opposite) and one for earth. To pick up the signal, the potentiometer has two wiper outputs, which pick up the voltage in the potentiometer at the resistor track offset by 90°. This makes a total of five connections / contacts. There are also components similar to potentiometers, so-called rheostats (adjustable resistors). These usually require only two connections for their switching mode (rheostat circuit). So if adjusters have only two connections, this is an indication that the component is not a potentiometer but a rheostat. However, we do not offer rheostats in our product range.

Potentiometer technologies

Our precision potentiometers are available in three different resistance elements (technologies). The respective resistance element is largely responsible for the quality and function of the application.
Wirewound potentiometer
  • In principle, they can also be used as variable resistors (in a so-called rheostat circuit). However, we recommend the voltage divider circuit, as the components are designed for this purpose.
  • Available in so-called single-turn (<360°) and multi-turn (>7200°) versions.
  • They have a limited lifespan due to wear and tear and due to the winding jumps of the wire windings "steps" in the output signal, which manifest themselves as noise when the wiper moves.
Conductive plastic and hybrid potentiometer
  • 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 for multiturn potentiometers
  • They have a significantly longer lifespan because the resistance track is very smooth, they have a theoretically infinite resolution, a particularly smooth output signal, outstanding linearity and allow higher adjustment speeds

Resistance elements in comparison

Resistive elementConductive PlasticWirewoundHybrid
Lifespan++0+
Signal quality / resolution+++++++
Linearity++++++++
Electrical travelmax. 360°10800°max. 3600°
Operational speed++-+
Max. wiper current--+--
Shock / Vibration-----
Legend: +++ best | ++ very good | + good | 0 OK | - low | -- unfavourable | --- not appropriate

Multiganged / Tandem Potentiometer

If redundancy of the sensor technology is required in applications, so-called multiganged potentiometers or tandem potentiometers in double version are often used. The overview of all multiganged potentiometers can be found here. The field of application ranges from mechanical engineering to aviation. To ensure that the tight linearity tolerances of the potentiometers maintain their quality, it is important to ensure that the heat generated during operation does not have a negative effect on the properties of the potentiometer due to the adjacent design. It is therefore necessary to reduce the nominal load according to the table.
These specifications/measured values apply under standard conditions (+15 °C to +35 °C). If the potentiometers are used at higher temperatures, the load must be reduced.

Multiganged Potentiometer AL17/19

*This graph does not apply to the oil-filled potentiometers.


Oil-filled potentiometers

Oil-filled potentiometers are usually employed 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 lifespan, as the oil filling suppresses corrosion at or near the wiper.
Some applications of these potentiometers are e.g. control systems in areas such as shipbuilding, electrical installations on the coast, pits and mines, ironworks, chemical plants, unmanned underground installations and machine tools.  However, some applications may require additional approvals, such as explosion protection, which must be obtained separately for each application. The overview of all oil-filled potentiometers can be found here.

OF50 - oil-filled


Measuring amplifier / signal converter for potentiometer

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 generate standardized signals in a simple design, we offer measuring amplifiers that allow standardized signals to be obtained by means of an external power supply.

Circuit types

Voltage divider circuit

Operate the potentiometer in the voltage divider circuit and limit the wiper current to a minimum. Only in this way will the potentiometer retain its optimum lifetime characteristics and optimum signal quality.
  • The tolerance of the total resistance is not relevant
  • The temperature influences are almost completely suppressed
The voltage divider circuit offers the advantage of high robustness against parasitic resistances between resistor element and wiper. Only in the voltage divider circuit you can take full advantage of the special design features of each potentiometer type depending on the application.

Rheostat circuit

Do not operate the potentiometer in two-wire technology, as a variable resistor or rheostat. This type of circuitry has considerable disadvantages with regard to signal quality and lifespan of the potentiometer and is only possible for wirewound potentiometers (at low load). Conductive plastic and hybrid potentiometers are damaged in this type of circuit!

Total resistance

A high total resistance is advantageous in applications where low power is required. A low total resistance is advantageous in applications requiring "optimum" signal quality.
  • 500k potentiometer - for very low power applications
  • 100k potentiometer - often for battery powered applications
  • 10k potentiometer - standard applications

Center Tap

With this option you have the possibility to use an additional tap on the resistor track, which is realized as center tap at half resistance value corresponding to 50% of the electrical angle of rotation. This makes it possible, for example, to operate the potentiometer bipolar, i.e. to apply positive and negative voltage to the terminals of the resistance element (terminals 1 and 3), while the center tap is connected to ground. The center tap is for applications which ensure that the voltage value remains the same in the center position of the potentiometer throughout the life of the potentiometer, or if the output value is to be divided into two ranges. Please note that there are two possible implementations of this tap:

Voltage tap and current tap

Voltage tap

The voltage tap cannot take a load. Therefore, no current should flow over the center tap, otherwise the component is destroyed. The following applies to the circuitry of the voltage tap: If the center tap is connected to ground and the end taps are both at negative and positive potential, currents should be prevented from flowing via the center tap by connecting an operational amplifier. If only voltage of one polarity is applied from one end to the tap connected to ground, a too large current will flow at the intermediate tap. In this case, the voltage applied between terminals 1 and 3 must in any case be reduced below 50% of the rated voltage (less than 10% is recommended).

Current tap

The current tap influences the linearity of the component to a certain extent. Please contact us directly for more information about the sensor's characteristics regarding this special connection. Joysticks are an example application for current taps: For a voltage range of 0 to 5 V within the travel range, the Center Tap is 2.5 V, which corresponds to non-actuation. Even when certain areas of the resistor track are worn out, the value at center tap always remains 2.5 V and no "wrong" output signals are generated. Here current taps are used throughout, because a certain current flow over the center tap can be expected.

Environmental influences

Vibration and shock effects In general, it is recommended to avoid the effects of vibrations and shocks on potentiometers. Depending on the strength and frequency of these influences, the wiper can "lift off" from the resistor track, resulting in signal loss at these moments. In addition, these influences lead to increased wear on the resistor track, which results in losses in signal quality and decreased lifespan. Wirewound potentiometers are somewhat more robust and more suitable for low frequency applications than conductive plastic potentiometers.
Temperature influences Our potentiometers are specified under standard conditions at room temperature (+15 °C to +35 °C). Lower or higher temperatures can influence the signal quality, for example by freezing humidity in the air or by evaporating grease and laying on the resistor track. Furthermore, the temperature influences the operating torque. The use of appropriate seals or special greases can help. We would be pleased to support you with the appropriate requirements for your application.
EMC/ESD compatibility Potentiometers are analogue, "passive" components that do not contain any electronics that could restrict the EMC or ESD properties. Potentiometers are therefore considered insensitive to electromagnetic interference, which is a great advantage in critical applications.

IP protection class

Nearly all our potentiometers are specified with protection class IP40 and nearly all of them can be increased to protection class IP65 with a shaft sealing ring on the shaft side. If a higher degree of protection is required, e.g. for the housing, the MFP500 and AL17IP (OFH, OF5001, OF30, OF50) fulfil this requirement. For many potentiometer series there are options available which allow a sealed housing.
First Digit: Solid particle protection
IPDegree of protection
0Non-protected
1≥ 50 mm
2≥ 12.5 mm
3≥ 2.5 mm
4≥ 1 mm
5Dust
6Dust-tight
Second Digit: Liquid ingress protection
IPDegree of protection
0Non-protected
1dripping waters
2dripping water when tilted at 15°
3spraying water
4splashing of water
5water jets
6powerful water jets
7immersion, up to 1 meter depth
8immersion, up to 1 meter or more depth

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 @ room temperature). In addition to the pleasant haptic properties, an increased rotational resistance prevents unintentional adjustment due to machine vibrations. A wide range of pre-assembled sets and adjustment knobs are available for your application. See rotary potentiometers

Mechanical stops & slipping clutch

Mechanical stops In most cases the mechanical end stop is used for applications for manual setpoint setting. Please note the maximum permissible end 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 permanently stressed, it can wear out more quickly and its lifespan is shortened. Please consider this effect.

Operating notes

Applications with very rare actuations According to the motto "resting is rusting", the slider behaves in relation to the resistance track. Oxide/sulphide deposits can form. Please contact us to take suitable countermeasures in advance. For example, an increased contact pressure for the slider or appropriate seals promise to help.
Applications with very short continuous actuations Please note that if the actuation travel is always the same and at the same time very short, the resistance element will experience increased wear at this point and the lifespan will be reduced. At the same time, microscopically small abrasion mounds are formed on the resistance element at the actuation ends, which influences the signal quality. Periodically passing over these points can clean the resistor track.

Shaft load & tightening torques

Tightening torques for threads and screws Please take note of the tightening torques as well as dimensions for threads and screws to avoid damaging the potentiometer. Especially for potentiometers with a bushing, the torque of the shaft can be increased if mounted improperly. For mounting the servo flange potentiometers, corresponding synchro clamps are included in the delivery.
Mechanical coupling Do not subject the shaft to excessive axial and radial loads in the long term. Normally, values of < 1 N do not pose a problem. Some potentiometers have a reinforced shaft bearing and allow values with < 4 N (e.g. ALI17/19). Use a shaft coupling to minimize existing shear loads (axial and radial loads). When installing additional components such as shaft coupling, gear wheels or similar, please ensure that the shaft is not permanently loaded with more than 10 N. Short-term loads of this magnitude are no problem.

Adjustment, mounting types and soldering instructions

Zero point adjustment The zero point adjustment can be conveniently made with a screwdriver slot on the shaft. The possibility of integrating 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 first.
Soldering note Use a soldering iron with max. 60 W (<350 °C) for soldering the connections and do not contact with them more than three seconds.
Installation types For panel mounting, the potentiometer with shaft must be mounted in a precisely machined hole without play. For potentiometers with a fixing pin, the so-called anti-rotation pin, please include a corresponding drill hole. With hollow shaft potentiometers, a rigid fixing of the housing must be avoided. This is because the hollow shaft is not suitable to take over the bearing function of the actuating shaft. The specifications in the data sheet for housing depth and housing diameter do not take into account the dimensions of the electrical connections. If the installation space is limited, please take into account above all the alignment of the connections and the additional space required for these.

Frequency Effect

Use in high frequency technology Due to the mechanical construction, especially of multiturn potentiometers (wire winding), potentiometers have different values for inductance and capacitance, which must be taken into account in circuits of high frequency technology. These properties lead to phase shifts between current and voltage as well as to damping effects. However, in wirewound potentiometers (also hybrid potentiometers) these effects typically only occur at frequencies above 20 kHz. With conductive plastic potentiometers, these effects are negligible up to about 200 kHz, as there is no winding.

Hysteresis / Backlash

When the wiper passes over the resistance path in one direction, a certain electrical value (U1) is reached at a certain point (α1). If the slider is moved in the opposite direction, the same electrical value is reached at another point (at another angle, α2). This difference is expressed in angular degrees and is called hysteresis or backlash. The 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 are dependent on the direction of the wiper.

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 optimum straight line is drawn through the actual output voltage curve, so that the deviations of the curve from the straight line are minimized. The distances (delta) in the figure represent the specified independent linearity, this is given as a percentage. 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. In addition to the wide range of options available for our sensors, we offer specific designs which exactly meet your application requirements, even in small quantities. Whether it is a prototype project or a series production - we are happy to support you.

The boundaries between standard and non-standard articles are fluid. The abundance of options makes it practically impossible to present every electrical and mechanical combination possibility or even to stock them as physical articles. Even with a relatively simple potentiometer, the variety of articles would amount to xn (several hundred to a thousand variants). Therefore, we have highlighted those product options in the data sheet which have a high acceptance on the market and declared them as standard. The choice of options often involves electrical or mechanical adjustments to a product. In addition, we realize product adaptations that go beyond the options in the order code and give examples of further possibilities. It is precisely the ability to optimize the product to the requirements of the application that distinguishes us. Therefore, it is important for us to know the application and the area of use as well as possible. In this way we can determine the technical possibilities and economic implementation of the product you are looking for and at the same time examine our entire product portfolio. Within the scope of our consultation, we determine your article that meets the requirements and, if necessary, suggest alternative products if they offer you advantages in terms of economy and technology.

Mechanical optimizations and beyond

Assembly of cables and connectors

Please define your application requirements with regard to environmental conditions and installation situation - if desired, we will take over the operative implementation such as procurement and assembly of cable and connectors for the offered article. Everything from one source - save time and money.

Mounting of mechanical components

For the mechanical coupling to the application, we operatively implement the attachment of mechanical components such as gear wheels, spring plates and much more on the offered potentiometers. On request, we can determine, procure or develop all necessary components for the optimal connection.

Optimization of the shaft

In our data sheets we list the possibilities of adapting the potentiometer shaft for your application: Whether it is the shaft diameter, the shaft geometry or a continuous shaft, also with the possibility of adapting the diameter up to the geometry. In addition, we make adaptations on the bushing for the optimal connection to the application.

Torque optimization

In principle, it is possible to adjust the torque for all potentiometers. We use special lubricants with appropriate viscosity, which are adapted to the application and the ambient conditions. For example, in applications requiring a sensitive change in position, sensors with a comparatively low actuating torque are used. If an unintentional setpoint change due to incorrect operation is to be prevented from causing damage to the machine or life and limb, potentiometers with a higher torque are used.

Increasing the IP protection

Depending on the environmental situation, it is often necessary to increase the IP protection for the potentiometer. On the one hand, we offer sealing elements for the shaft, which protect against moisture and dust, and sealing elements between the panel and the sensor. Furthermore, there is the possibility to seal the housing. In many cases a potting of the housing is required, but also completely housed potentiometers are available. Please contact us and specify your requirements.

Electrical optimizations

Optimization of the electrical and/or mechanical angle of rotation

We offer a very wide and deep product range for potentiometers. Nevertheless, some applications require an adjustment of the mechanical angle of rotation by end stops and/or electrical angle of rotation by limiting the output curve, so that the potentiometer optimally meets the requirements.

Optimization of linearity and resistance values

For demanding applications we offer the optimization of linearity and/or resistance values, in addition to the values already mentioned on the data sheet. Our potentiometers are manufactured in a highly tempered production process. Therefore, we are able to meet these requirements within the scope of technical possibilities.

Zákaznické přizpůsobení potenciometru

Pokyny pro seřízení, montáž a pájení potenciometrů

Seřízení nulového bodu Nulový bod lze pohodlně seřídit pomocí zářezu na šroubovák na hřídeli. Zářez pro šroubovák v hřídeli je ve všech sériích s hřídelí a u některých z nich je již standardně implementován. U potenciometrů se servo přírubou je možné seřízení nulového bodu pouhým otočením pouzdra potenciometru. Pro tento účel musí být nejprve uvolněny svorky. Pájecí pokyny: Používejte měkkou pájku s max. 60 W (<350 °C) a nepájejte déle než tři sekundy. Možnosti instalace Pro montáž na panel musí být potenciometr s hřídelí namontován v přesně obráběném otvoru bez vůle. Pro potenciometry s upevňovacím kolíkem, tzv. kolíkem proti otáčení, prosím, zvolte odpovídající otvor. U potenciometrů s dutou hřídelí je třeba se vyhnout pevnému upevnění pouzdra. Je to proto, že dutá hřídel není vhodná k nosné funkci při pohybu hřídele. Specifikace v katalogovém listu o hloubce a průměru pouzdra nezohledňuje rozměry elektrických přípojek. Pokud je instalační prostor omezený, vezměte v úvahu především uspořádání výstupů a další prostor potřebný pro ně.