Wirewound Potentiometers

Features and advantages of wirewound potentiometers

# Wirewound Potentiometers

## In multiturn and singleturn versions

Wirewound potentiometers cover angles up to 10800°. They achieve top ratings for linearity and resistance tolerances. Special functions such as center taps or limit switches can also be integrated. The components have slightly higher tolerances for the permissible wiper current, which can be a relevant selection criterion in special applications.

The portfolio of wirewound potentiometers is divided into single-turn variants (up to 355°) and multiturn products (up to 10800°). The offer goes from miniaturized versions, with the smallest 10-turn potentiometer in the world, to versions with reinforced shaft bearings of up to 4 N. Despite the wide selection, these products often require technical product adaptations to best meet the requirements of the application.

MEGATRON is your partner for the optimal adaptation of the product to your application. 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.

Guide for Wirewound Potentiometers
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## Resistance element of wirewound potentiometers

The production of the resistor element for wirewound potentiometers demands high precision mechanical requirements in the production process and only a few manufacturers today are up to this challenge: A hair-thin resistance wire is wound around a carrier core under a defined tension. Depending on the desired total resistance value, different metal alloys are used and depending on the total resistance value the number of wire windings around the carrier core is determined. When tapping the voltage potential, the wiper only touches a small part of the winding surface. However, this surface is not completely flat due to the windings. For this reason, wirewound potentiometers produce so-called winding jumps in the output signal, which manifest themselves as small steps.

Wirewound Element

## Resolution of wirewound potentiometers

High resistance wirewound potentiometers have a higher resolution
The easiest way to achieve better resolution with wirewound potentiometers is to increase the number of windings. This makes the windings denser and the jumps in the output signal described above become smaller. As the wire length increases, the total resistance value increases. Depending on the application, this is an advantage, e.g. if a low power dissipation is desired. Due to this correlation, a compromise between resolution and total resistance must often be made when selecting the parameters.

Formula for calculating the resolution:

Example series RP19/20

• maximum electrical travel is 355°
• @ 5kOhm 1000 windings

Formula: 355° / 1000 turns = approx. 0.355 degrees

Formula for calculating angular degrees:

$$θ = \frac {Vout} {Vin} * \text{effective electrical angle of rotation}$$

Example: $$θ = \frac {4} {5} * 355° \approx284°$$

If approx. 4 V is measured at the slider with a total angle range of 0° to 355° and a voltage range of 0 to 5 V, this would correspond to an angle of approx. 284°. However, this is a theoretical value, as potentiometers have backlash at the end positions and resistance tolerances.

## Circuit methods of wirewound potentiometers

The permissible load of the signal output is limited by the maximum permissible wiper current. In principle, wirewound potentiometers are also suitable for applications with a so-called rheostat circuit as a variable resistor, where a certain base load occurs. Nevertheless, we recommend the voltage divider circuit, because only then can one fully profit from the quality and function of our wirewound potentiometers.

However, potentiometers with wire-wound technology can be of use in some applications (e.g. when using older programmable logic controllers) where there is no possibility of implementing a voltage divider circuit. Within the specified performance limits, they can withstand straining wiper currents without suffering damage.

## Load capacity of the resistance element

 Example Voltage U Resistance R Power P Application possible? 1 20 V 1 kΩ 0.4 Watt yes 2 30 V 1 kΩ 0.9 Watt no 3 30 V 5 kΩ 0.18 Watt yes 4 100 V 10 kΩ 1 Watt no 5 100 V 20 kΩ 0.5 Watt yes

Example RP22/23 series

• available resistance values (10...500Ω) 1, 2, 5, 10, 20 kΩ
• max. load capacity 0.5 Watt

The following applies to power loss:
P = U² / R (power P = voltage U² / resistance R)

On the basis of this calculation example, it is immediately evident that at an operating voltage of 30 V, the potentiometer with 1 kΩ cannot be used because otherwise the power with which the resistor element is loaded becomes too high. Please also take into account the additional restrictions for the ambient temperature.

## Resistance elements in comparison

 Resistive element Conductive Plastic Wirewound Hybrid Lifespan ++ 0 + Signal quality / resolution +++ + +++ Linearity +++ ++ ++ Electrical travel max. 360° 10800° max. 3600° Operational speed ++ - ++ Max. wiper current - + - Shock / Vibration - -- --

Legend: +++ best | ++ very good | + good | 0 OK | - low | -- unfavourable | --- not appropriate

## Decision support

Wirewound potentiometers are available as single and multiturn versions. With wirewound potentiometers very good linearities and very high electrically effective angles of rotation can be achieved; for singleturn up to 355° and for multiturn up to 10800°. Wirewound potentiometers are the right choice for applications with high demands on resistance tolerances.

RP19/20 singleturn

Series 46 multiturn

### Wirewound compared to conductive plastic potentiometers

Due to the uneven nature of the winding of the resistance wire, the output signal is slightly stepped. Furthermore, a higher electrical noise is generated over time due to the higher abrasion than it is the case with conductive plastic or hybrid potentiometers. The best linearity, however, is achieved with conductive plastic potentiometers. In addition, the lifespan of conductive plastic potentiometers is the highest among all technologies.

The wire technology is somewhat more robust against low-frequency shock and vibration loads compared to conductive plastic potentiometers. However, we recommend, if possible, the use of sensors based on contactless measuring principles in case of vibration influences.

With very slow throughput movements, a "creeping" contact is created between the wiper and the resistance element. Under such conditions a safe electrical transition is only guaranteed if a certain minimum current is applied to the contact. Experience shows that about 100 μA on the slider are sufficient for this purpose. However, we recommend the use of conductive plastic or hybrid potentiometers for such measuring tasks with very slow displacement movements.

Wirewound potentiometers are not suitable for operating speeds above 40 rpm. For higher demands our conductive plastic and hybrid potentiometers are designed for speeds up to 400 rpm.

Limit switches are used on some models, especially in the safety-critical area. These detect when a multiturn potentiometer has reached the mechanical end position. The microswitches used have separate connections and their own specifications regarding maximum power consumption.

### Wirewound potentiometers are often used as panel encoders

Multiturn potentiometers with wire-wound resistors are often used for setpoint setting in hand-held applications, because long lifespan characteristics and extremely precise tolerances such as those of hybrid potentiometers are usually secondary for these applications. In addition, the slightly better shock tolerance of wirewound potentiometers in the low frequency range can be an advantage for these applications. Hybrid potentiometers are used when long lifespan, excellent linearity and a high electrically effective angle are required.

## Product customizations

Our wirewound potentiometers are available in bushing or servo flange versions with their special features. A variety is available with or without mechanical stop, with optional rear shaft, center tap(s) and in tandem / multi-turn versions. As special versions, we offer adaptations such as axis modifications, special torques, sealed housings, special electrical and mechanical rotation angles, special resistance and linearity tolerances, assembly of gear wheels and other mechanical parts, assembly of cables and connectors, and much more. As a specialist for industrial sensor technology, we are the ideal partner for your application, since we have the highest quality standards and delivery reliability in addition to meeting your technical requirements.

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