1905

Adjustable resistors use the same basic construction as fixed resistors already described, and have a window in the vitreous enamel through which contact is made to the resistive element by a sliding contact band. The band is fitted with a clamping screw and nut to retain it firmly in position.

The adjustable winding style has a maximum permissible hot spot temperature of 300°C and the maximum dissipation, for an ambient temperature of 20°C, is specified in Table 4. The partial open winding necessitates a reduced maximum resistance, when compared with fixed resistors, and the resistance range is also defined in Table 4.
More than one adjusting band can be fitted, up to the maximum number specified in Table 3.

Adjustable resistors are available in termination styles B, 4B, AP, C, CB and CP, in sizes 1602 to 1609 inclusive and 1906 and 1908 denoted by prefix 'V'.

Vitreous enamelled wirewound resistors are capable of withstanding a higher dissipation size for size, than any other protected type; this is attributable to the higher operating temperature which the wire and enamel can withstand.
Vitreous enamel provides exceptionally good protection to the wire element and is essentially impervious to moisture.

The resistors 1905 can safely be used in harsh environmental conditions.

The Welwyn range 1905 is based on thirteen sizes of tube, each of which has a recommended maximum dissipation which limits operating surface temperature to a maximum of 375°C.

The stability and high reliability of Welwyn tubular vitreous resistors 1905 is a direct result of the best quality materials being used in their construction.

High purity ceramic tubes have been matched with nickel chromium resistance wires and specially formulated enamel to ensure that the resistors can withstand repeated heat cycling without damage. Connections between the resistance element and end terminations are welded; other connections are brazed.

Mounting devices 1905 are available which permit resistors to be mounted by both ends or by one end. Single ended mounting is recommended for applications which do not subject the resistor to shock or vibration.

Ferrules and the F type mounting plug 1905 are anchored into the tubes with high temperature adhesive.