• Ultronix, Inc

Wirewound Resistors

Ultronix RBR Series high precision wirewound resistors are constructed to eliminate thermal EMF (unwanted parasitic voltage). This is accomplished in Ultronix wirewounds by making the interface between the resistance wire and the two lead connections almost touch, ensuring that there is not any significant temperature difference between them. In addition, these junctions are buried deep inside the body of the resistor. Further, UlLronix makes their own bobbins and uses the same material to mould the outside, so there is a compatibility of materials. Also, uniform resistance windings provide consistency between products. This Ultronix construction is significantly different and offers much improved performance when compared to other wirewound resistors on the markel Other constructions use a moulded bobbin with a small metal alloy tab which is different than the resistance wire. Then a lead wire of a different metal is attached to the tab. Thus, one has three different alloys, all of which have different Seebeck coefficients, resulting in a very large thermal EMF. This situation, in addition to the fact that there is significant space between the leads, results in high thermal EMF as the resistor changes temperature. Ultronix units are manufactured using two materials and the linear coefficients of thermal expansion are similar, promoting excellent stability during thermal cycling. All materials used in the resistor construction are carefully selected for their mechanical, electrical, and thermal characteristics and for their compatibility with other components of construction (leads, bobbins, encapsulants, insulation). Electrical specifications are: Maximum resistance value: 1.37 MW; Minimum values: 0.1 W for ? 1% and 10 W for ?0.1% and tighter (except RBR74 = 100 W and RBR76 = 18.36 W); Resistance tolerance: ?0.01% to ?1.0%; Temperature coefficient: ?90 PPM/?C to ?10 PPM/?C; Power rating at 125?C: from 0.125 to 0.750 W; and Short time overload: twice rated power.