Downloaded from https://www.everyspec.com AMCP 70"N identical at all locations. If this is impossible, but actual measurements should be made to the differences should be held to an absolute verify the calculations before the test minimum and should be known and evalu- equipment is released for use. In such cal- ated carefully to determine the exact cluanti- culations, provided they are verified, it is tative differences. There are several potential generally permissible to use statistical tech- sources of error.
The most important are niques to combine tho individual errors in- those introduced by the use of supposedly troduced by the many elements of the test identical or interchangeable equipments which equipment, are not really identical or interchangeable. This problem can be minimized by assigning 9-5 TEST EQUIPMENT CALIBRATION the design of the test equipment to a single group and by instructing the design group to Automation in complex weapon systems use the same testing techniques and circuits has tremendously increased the importance throughout the project. The uniformity of of calibrated test equipment.
Because of the purchased test equipment is more difficult increased number and dispersal of the sup- to control, since competitive procurement pliers, manufacturers, and field activities that procedures lead to pressures to accept ap- test all or part of these systems, test engine- parently or allegedly alternate and Inter- era must give consistent and compatible re- changeable instruments without complete suits. comparative evaluation or analysis. Test personnel must constantly resist this pres- Another major source of test errors is a sure - the world is rarely as advertised and poor calibration system which is not rigor.
the difficulties can be very subtle and in- ously traceable to the standards of measure- sidious. ment held by the National Bureau of Stan- dards (NBS), 9-4 TEST EQUIPMENT ERROR Test equipment incompatibilities can All measuring equipment has an inherent result in major catastrophic failures. error, The amount of the error i& frequently an important portion of the alloviable or Calibration is defined as the comparison desired tolerance on the parameter being of the indication of a measuring device with tested, so that considerable degradation of a known standard, the known standard it- the product can result from ignoring test self being calibrated against more accurate equipment error.
Test equipment error exists standards in a series of rigorously controlled not only in the reading or sensing portion of echelons up to a national standard held by the test equipment, but in the portions pro- the NBS. All test and measuring equipment viding the inputs and environmental con- used in high-reliability projects, including ditions as well, those used by R&D personnel, must be call- brated against laboratory standards at speci- The total error always should be measured fled intervals. These intervals should be set for complex special test equipment.
The after thorough analysis of drift rates or sus- measurement is best made at the Interface ceptibility of instruments to inaccuracies between the test leads and the article to be from handling. tested (where it will include the ei or of the cabling and connectors), with the equipment A system of mandatory recall usually is and the article both energized and operating, required to ensure satisfactory operation of Theoretically-computed errors can be use- a calibration program, since most test op- ful during the test equipment design phase, erators are slow to release instruments for "I It r I I_