This technology enables to propose Power Resistors with high Resistance values (up to several hundred ohms).
Moreover, these resistors are particularly well adapted to applications requiring high voltages (continuous and transitory).
THE RESISTIVE WIRE
It is the woof of the mat. The wire diameter can vary from 0.3 to 2mm.Various alloys are available as standards (from Konstantan which has a zero temperature coefficient, to stainless; steel type alloy or iron-chrome-aluminum). The P distance (Fig 1) varies accordingly to the wires nature and diameter, and is usually between 1 and 5 mm.
THE CHAIN WIRE
It has to maintain the resistive wire as well as to keep an optimum coefficient of thermal exchange. A E class fiberglass is proposed as a standard. It presents the following advantages:
- high temperature withstanding :
- above 450’C for short time ratings
- low coefficient of linear thermal dilatation. The mats have a low length variation according to temperature which makes the fixation simple.
- excellent hot mechanical tensile stress resistance,
- strong resistance to pollution (except fluorine pollution).
A wide range of materials (cotton, kevlar, silica fiber) can be proposed for specific applications.
DIMENSION AND DESIGN
The weaving process provides a large flexibility in the choice of the L and 1 dimensions.
However, in order to rationalize our products, we propose 2 standard widths :160 mm and 250 mm.
The plain strips at the ends are used for mechanical fixation and can also take part to the electrical insulation.
We currently use two different arrangements (Fig.2) : the mats can be used as independent resistors, either fixed between 2 supports ensuring the insulation, or in a ” U ” form , or rolled, to give them a sufficient inertia, in order to be self standing. In most cases, they are used in banks and connected in series or in parallel, or in a combination of both.
- harmonics filter
- low discharge of high voltage capacitors
- infrared heating
- they are also dedicated to applications where space limitations necessitate a specific and sometimes complex mechanical design. This occurs in small heating units.