scope:

This specification covers the general requirements for lead-screw actuated, wire-wound, variable resistors with a contact bearing uniformly over the surface of the entire resistive element, wound linearly, when positioned by a multiturn lead screw actuator. These resistors are capable of full load operation (when the maximum resistance is engaged), at a maximum ambient temperature of 85°C and are suitable for continuous operation, when properly derated, at a maximum temperature of 150°C (see 3.6), with a resistance tolerance of ±5 percent. The resistors will have life failure rate levels ranging from 1.0 to 0.001 percent per 1,000 hours (see 1.2.1.5). These failure rate levels are established at a 60-percent confidence level and maintained at 10-percent producers risk on the basis of life tests. The failure rate level, identified by the appropriate symbol, is referred to operation at full voltage at 85°C, with a permissible change in resistance of ±3 percent plus the specified resolution as the criteria for failure. Table I of supplement 1 provides a summary of performance characteristics for these resistors. A part per million (PPM) quality system is used for documenting and reporting the average outgoing quality of resistors supplied to this specification. Statistical process control (SPC) techniques are required in the manufacturing process to minimize variation in production of resistors supplied to the requirements of this specification.

The PIN shall be in the following form, and as specified (see 3.1). Beneficial comments (recommendations, additions, deletions) and any pertinent data which may be of use in improving this document should be addressed to: US Army Laboratory Command, ATTN: SLCET-R-S, Fort Monmouth, NJ 07703-5000, by using the self-addressed Standardization Document Improvement (DD Form 1426) appearing at the end of this document or by letter.

The style is identified by the three-letter symbol "RTR" followed by a two-digit number; the letters identify established reliability, lead-screw-actuated, wire-wound, variable resistors, and the number identifies the physical size.

The characteristic is identified by a single letter which identifies the resistance-temperature characteristic, maximum ambient temperature at rated wattage, and maximum ambient operating temperature (zero load) in accordance with table I. TABLE I. Characteristic.

Symbol Maximum resistance Maximum ambient Maximum ambient temperature characteristic temperature at operating (referred to 25°c) rated wattage temperature % °C PPM °C °C D..... ±0.005 ±50 85 150 -------------------------------------------------------------------------------------

The terminals are identified by a single letter in accordance with table II. TABLE II. Terminals.

------------------------------------------------------------------------------- Symbol Type of terminal ------------------------------------------------------------------------------- L Flexible, insulated-wire leads P Printed-circuit pins W 1/ Printed-circuit pins (edge mounted) X 2/ Printed-circuit pins (edge mounted, alternate configuration) Y 3/ Printed-circuit pins (staggered) ------------------------------------------------------------------------------- 1/ Available only in essentially square styles. Pins extend from the edge 180° away from the screw head, and are parallel to the longitudinal axis of the lead screw. 2/ Available only in essentially square styles. Pins extend from the edge 90° away from the screw head, and are perpendicular to the longitudinal axis of the lead screw. 3/ Applicable to style RTR12 only.

The nominal total 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. The following are examples of symbols for resistance values:

101 = 100 ohms 102 = 1,000 ohms

The life failure-rate-level designation as shown in table III is signified by a single letter (M, P,R, or S), which identifies the life failure-rate level for which the resistor is qualified (see 4.5). TABLE III. Failure rate level (at 60-percent confidence).

------------------------------------------------------------------------------ Failure-rate level Failure rate designation percent/1,000 hours M........... 1.0 P........... 0.1 R........... 0.01 S........... 0.001 -------------------------------------------------------------------------------

intended Use: