MAINTAINABILITY DESIGN TECHNIQUES METRIC - AcqNotes.com

Downloaded from http://www.everyspec.com on 2011-10-29T14:56:01.DOD-HDBK-791(AM)power plant, transmission, and power train---the directionof the impetus (power) is from the engine to thepower train, not the reverse.Guidelines to be followed are1. Package and locate components parallel to theirfunctional relationships as established by a flow chart.Fig. 5-1 illustrates this idea.2. Select methods and subassemblies so that only asingle input check and single output check are required toisolate a fault within an item.5-5.2.2 Circuit GroupingCircuit grouping is the technique of grouping circuits—electric, hydraulic, or power for a specific function, e.g.,the audio and video circuits of television receivers andrecorders. Guidelines to be followed are1. Locate all parts of a given circuit or logicallyrelated group of parts—e.g., an automotive transmission- -together in a common volume.2. Place each circuit within the group in a separatemodule, e.g., a printed circuit board of the plug-in typethat can easily be replaced.5-5.2.3 Component GroupingComponent grouping is the technique of groupingtogether components with similar functions or that possesscommon characteristics. Guidelines to be followedare1. Locate items together that perform similarfunctions—e.g., amplification circuits, fuses, and relays.2. Segregate resistors, capacitors, and transistorsinto a minimum number of different locations on subassembliesand terminal boards.3. Group inexpensive components on a single chassisto Facilitate throwaway at failure.4. Group gages and instrument readouts—necessaryfor the control or monitoring of a function—into aninstrument panel to facilitate operator surveillance.5. Segregate components on the basis of significantvariations in the required maintenance tasks. For example,items that are to be cleaned by different methods—steam or solvent--should be packaged so that cleaning ispossible with minimum masking.5-5.2.4 Standard ConstructionStandard construction is a technique that follows nopreconceived set of rules. This construction creates a finalproduct by balancing a number of factors- heat loss,component size, final unit size and weight, and eyeappeal—to arrive at a compromise, which varies for eachapplication of the standard item. Examples of such acompromise are the simple radio receivers available onthe civilian market—they are configured in headsets,hand-held portable radios, clock radios, etc., for consumerappeal.5-5.2.5 Frequency GroupingFrequency grouping is the technique of grouping multiple,similar parts that are likely to require replacement atthe same time. This technique is most beneficial if thedominant failure mode is wear, fatigue, or a similar agedependentmode. Periodic replacement of assembliesbecause of anticipated failure makes possible a systemthat is, for all purposes, rebuilt.5-5.2.6 Evaluation of Grouping MethodsAn empirical evaluation of the previously describedequipment grouping techniques was performed by techniciansof different skill levels on a simple system and acomplex system (Ref. 3). Based on the performance dataused to make the evaluation—troubleshooting time,amount of information gained per unit of time, technician’ssubjective performance, and engineering criteriaitwas determined that the logical flow method is superiorto the standard construction method because the logicalflow method clearly enhanced the ease of equipmentmaintenance. The other grouping techniques also werepreferred to the standard construction method; however,Figure 5-1.Design for Functional Utilization That Corresponds to Modularization5-5