scope:

This specification covers power, wirewound, adjustable resistors for use in electrical, electronic, communication, and associated equipment. These resistors have a resistance range of 1 to 15,000 ohms, inclusive, and a resistance tolerance of ±5 percent. The power ratings (see table II and 3.1) cover a range of 11 to 210 watts, inclusive. These power ratings are applicable only when the maximum resistance is engaged in the circuit. When only a portion of the resistance element is engaged, the power rating is reduced in approximately the same proportion as the resistance.

The type designation shall be in the following form, and as specified (see 3.1 and 6.1):

The style is identified by the two-letter symbol RX followed by a two-digit number; the letters identify power, wirewound, adjustable resistors, and the number identifies the size of the resistor.

The characteristic is identified by a single letter which identifies the maximum continuous operating temperature and the high-ambient-temperature derating of resistors, in accordance with table I. TABLE I. Characteristic

Maximum Symbol continuous operating Derating curve temperature ¹ ------------------------------------------------------------- V ............ 350°C (See fig.1) ¹ This temperature is also the maximum permissible hotspot surface temperature.

The nominal resistance value expressed in ohms is identified by a three-digit number; the first two digits represent significant figures and the last digit specifies the number of zeros to follow. Where fractional values of an ohm, and values of less than 10 ohms, are required, the letter R is substituted for one of the significant digits to represent the decimal point. When the letter R is used, the last digit becomes significant. The following are examples of symbols for resistance values:

1R0 = 1.0 ohm 100 = 10 ohms 101 = 100 ohms 102 = 1,000 ohms 103 = 10,000 ohms

Resistance values in all decades for all styles shall correspond to the values specified in the 10 to 100 decade listed below. For minimum and maximum nominal total resistance values, see 3.1.

Decade 10 to 100 of resistance values 10 18 33 56 11 20 36 62 12 22 39 68 13 24 43 75 15 27 47 82 16 30 51 91

The nominal power ratings for the various styles shall be in accordance with table II. TABLE II. Nominal power ratings (free space and still air 1)

Power ratings Style Characteristics V ------------------------------------------------- Watts RX29 .................... 11 RX32 .................... 17 RX33 .................... 26 RX35 .................... 55 RX36 .................... 78 RX37 .................... 113 RX38 .................... 159 RX47 .................... 210 ¹ Free space is predicated on horizontal mounting of the resistors with no object closer than 12 inches to the resistor, except the mounting base which shall be not closer than 2 inches below the resistors. Still air is air with no circulation other than that created by the heat of the resistor being operated.