ASME B89.7.3.3 pdf free download

ASME B89.7.3.3 pdf free download GUIDELINES FOR ASSSING THE RELIABILITYOF DIMENSIONAL MEASUREMENT UNCERTAINTYSTATEMENTS
3 THE NATURE OF DISAGREEMENTS iN UNCERTAINTY STATEMENTS
3.1 Generai In an ideal situation, customers and suppliers will address the issue of measurement uncertainty when they discuss uhe product specifcations. Agreeing on the measurement plan, the corresponding magnitude of the measurement uncertainty, and the decision rule (if applicabie), will avoid fuure disagreements regarding the acceptance/rejection of a pruducl. However, il is recognized thal lwU experts can produce two different uncerlainty statements often varying as much as 25% due to difering assuptions and data (as described in section 5). Rcsolving thesc diffcrenccs at the contract siage is potentially less contentious than doing so after an argumcnt devclops over the acceptance or rcjcction of the product.
3.2 Disagreements involving Single Measurement Systems In many situations there is only a single measurement system; e.g.. a customer agrces I0 accepl the supplier’s measurement results provided thal the supplier uses suringent acceptance with a 100% guard band (i.e., the guard band cquals the expanded uncerlainly). In his example, a disagteement may arise if the cuslomer feels the supplier has underestimaied the measurement uncertainly. Altough herc is a single measurement system, the supplier and the customer have devcloped diffcring unccrtainty statemcnts.
3.3 Disagreements Involving Multiple Measurement Systems In some situations, a customer and supplier both make measurements, each having their own measure- ment system and uncertainty statement. There are tWo cases to consider: first, when a product characlerisuic is being measured to assign it a value, e.g.. the length of a gauge biock, and second, when a product character- isuic is being measured to determine whether it conforms with specifications. In the frsl case, a best estimate of the value of山e product characteristic is being soughl. Two mecasure- menls, frurn differenl measurement systers, will give a better cstimate when their results are appropriately combined than will each system independently, provided the uncertainty statements associated with the measure- ment systems are valid. It is unlikcly that the mcasure- ments performed by the supplier and the customcr will yield exacdly the sarne value;however,agreementbetween the measurements is obiainedi by some exieniof overlap of the uncerlainty intervals. The extent ofoverlap should be specified in order to clearly idcntifywhen the parties arc in disagreement. (This avoidsdisagreements on what constitutcs a measurement dis-agreement.) There are several possible cascs of mctro-logical significance as shown in Fig. 1. Lct x; and xcbc thc mcasurcmcnt rcsults of the supplicr and customer,with respcctivc cxpandcd uncertaintics of U, and U.(both using a coverage factor of k = 2). Let A =– xd be the absolute value of the difference betweenthe measurements. Figure 1 illustrates this case withfive different pairs of measurements. The measurementsare considered to be in disagreement when A > U,+ and in agreement when A is less than the minimumof either U, or U. In laboratory round robins, measure-