BS 4889:1990 pdf free.Method for specifying thePerformance of electrical and electronic measuring equipment.
BS 4889 shall state rated values orspecified measuring ranges for all quantities whichhe considers to be performance characteristics
applicable to the particular equipment.
The manufacturer shall state a reference valueor a reference range and/or a specified operatingrange for each influence quantity which he takesinto account when specifying limits of error ofperformance characteristics.The specifiedoperating range shall include the whole of thereference range and usually exceeds it in at leastone direction.If any performance characteristic acts as aninfluence quantity, its measuring range is itsspecified operating range.If any performance characteristic appears as aninfluence quantity, its reference value or referencerange shall also be stated unless this is the same asits specified measuring range.
For any influence quantity not specified, its reference value or reference range is considered tobe its specified operating range.
Clause 15 provides information on reference valuesand reference ranges for some common influencequantities for use in compliance testing.Theinclusion of these values or ranges in a technicalspecification is not mandatory.
The worst-case error is specified with respect to therated operating conditions, and based on the limitsof intrinsic error and variations according to Type Aabove.To calculate the worst-case error, the moduli of themost unfavourable limit values of the intrinsic errorand variations are added up arithmetically.
The result of this statement of worst-case error doesnot depend upon the rules of statistics. For nearlyall conditions it does not represent the actual errorand it is likely to be too pessimistic.
Where operating error or worst-case error arestated, intrinsic error and limits of variations mayalso be stated.
NOTE When the intrinsic error and limits of variation are notstated, the manufacturer should provide them on request.
Several limits of operating error for oneperformance characteristic may be stated withrespect to several stated sets of rated operatingconditions.Errors may be specified either in absolute termsor in relative terms.In some cases, one part of anerror is expressed as a relative error whilst the otherpart of it is an absolute value, for instance (2 %+20 mV). In this case, thecalculation of an operating error according to Sub-clause and the calculation of a worst-caseerror according to Sub-clause 7.5 is done separatelyfor the relative parts and for the absolute parts ofthe intrinsic error and variations.
The value to which a relative error or fiducialerror is referred shall be clearly stated.That samevalue shall be used when more than one limit oferror is specified for a particular performance characteristic.BS 4889 pdf download.