Wire resistance
A wire resistor is a type of electrical component resistor .
General
The wire resistance is one of the original forms of electrical resistance and is still used today due to its properties. Sometimes it is also referred to as winding resistance.
The manufacture of wirewound resistors is relatively expensive (compared to other types) and their suitability for high-frequency applications is limited.
In the English-speaking world, these resistances are identified with the addition "wirewound".
construction
Resistance material
Typical alloys for the wire used are manganine and constantan , but also high temperature-resistant iron-nickel alloys .
Housing and contact
It consists of a ceramic or a temperature-resistant plastic body on which a wire with a suitable metal alloy is wound. Wirewound resistors are available uninsulated, with an insulating layer (glaze or cement) or embedded in a ceramic or metal tube. These resistors are only coded with colored rings for small designs . In most cases, the characteristic values are printed legibly.
Parameters
Resistance value
Wirewound resistors are particularly suitable for low resistance values , sometimes well below 100 ohms ; however, they are also manufactured up to resistance values of around 15 kOhm.
Tolerances
Common tolerances are 1%, 5% and 10% for high performance. However, they can also be manufactured with small tolerances, for precision applications down to 0.05%.
stability
Wirewound resistors are long-term and temperature stable. It is characterized by high power losses (up to approx. 2 kW) and operation at high temperatures of up to 800 ° C. The temperature coefficients range from ± 10 - ± 300ppm (corresponds to between 0.1% and 3% change in resistance for a 100 K temperature change).
A simply wound wire resistor is always a coil with a comparatively high inductance . As a result, its impedance depends on the frequency, which is usually undesirable. By properly winding the wire, this inductance can be greatly reduced:
- Up to 100 Ohm: ( Ayrton- Perry winding), bifilar winding
- From 100 ohms: winding according to chaperone. A whole winding layer has the same winding direction, the one above the opposite one.
- high resistance: winding according to Wagner-Wertheimer. Similar to the wires wrapped according to Chaperon bifilar, but divided into the smallest groups.
Noise
With wirewound resistors, the noise is essentially limited to thermal noise (Johnson noise), see heat noise . It is therefore much lower than the noise in the case of carbon-earth resistors, for example. Therefore, wirewound resistors are still used in critical applications.
Linearity
This component generally shows hardly any non-linearities.
Pulse resilience
The pulse load capacity of these resistors is high. They have a higher pulse load capacity than sheet resistors with the same thermal permanent load capacity, but tend to be below that of ground resistors.
Designs
Wirewound resistors are also available in standardized designs. They exist in the (axial) designs 0402 and 0207 (see also Resistance (component) ). The dimensions are usually determined by each manufacturer depending on the planned maximum permissible power loss and are therefore very different. Unwired versions in SMD technology are now available.
Areas of application
- measuring technology
- Performance applications
Voices and opinions from practice
Wirewound resistors are fairly straightforward to use in practice and therefore hardly noticeable.
literature
- Erwin Böhmer, Dietmar Ehrhardt, Wolfgang Oberschelp: Elements of Applied Electronics Springer Fachmedien Wiesbaden GmbH 2018, ISBN 978-3-8348-1496-8 , pp. 8–9
Web links
Individual evidence
- ↑ Ulrich Haenle: Resistance decades and rheostats. In: alte-messtechnik.de. May 6, 2019, accessed August 20, 2020 .
- ↑ Phil Ebbert: The wire resistance: "Reports of my death are greatly exaggerated". In: elektronikpraxis.vogel.de. December 20, 2012, accessed August 20, 2020 .