This is the sixth in a series of articles about MSA. The focus of this article will be on measurement repeatability and reproducibility for non-replicable measurement systems, commonly called a destructive test.

Okay, what exactly is a non-replicable measurement system and why is it not just called a destructive measurement system? Let’s start with the definition of replicate.

In statistics, a replicable measurement system is one where any given part may be measured multiple times by the same or different operators, and where the result obtained will fall within a predictable range of values.

By this definition, a destructive measurement system is definitely non-replicable. However, there are other situations that are non-replicable that do not result in the destruction of the part.

The following are examples of non-replicable measurement systems:

So, now you know you have a non-replicable test. What do you do? The following are several approaches that may work:

The next article will be:

Okay, what exactly is a non-replicable measurement system and why is it not just called a destructive measurement system? Let’s start with the definition of replicate.

In statistics, a replicable measurement system is one where any given part may be measured multiple times by the same or different operators, and where the result obtained will fall within a predictable range of values.

By this definition, a destructive measurement system is definitely non-replicable. However, there are other situations that are non-replicable that do not result in the destruction of the part.

The following are examples of non-replicable measurement systems:

**The part changes on use or test**(e.g., rubber parts will soften when flexed, harden when left alone and take a set when compressed; uncured rubber will cure when tested in a rheometer)**The characteristic is dynamic and is sensitive to multiple test conditions that cannot be exactly reproduced**(e.g., tests of complex systems such as an automobile)**The characteristic or property measured changes over time**(e.g., dimensions of freshly molded plastic parts, viscosity of materials with shelf lives)**The part physically cannot be reintroduced to the test**(e.g., in-line measurement devices)**The part is either physically destroyed**(e.g., tensile test) or**the part cannot be re-measured in the same location**(e.g., hardness test)

So, now you know you have a non-replicable test. What do you do? The following are several approaches that may work:

**Split specimens:**The parts or material collected to represent one part are split or sub-divided into smaller units. The smaller units are used for the repeat trials and between operator trials.**Consecutive specimens:**Consecutive parts are used to represent one part for the repeat trials and between operator trials. Used when the parts cannot be sub-divided and consecutive parts can reasonable be expected to be homogeneous, such as would occur in an auto-correlated process.**Regression approach:**The change in the characteristic over time or activity is known and has a defined relationship [Y=f(x)] (e.g., shrinkage of plastic parts). The subsequent measurements are adjusted using this relationship then analyzed.**Stabilized parts:**Parts or systems are stabilized before testing. This stabilization will depend on the product and characteristic. Some systems may be broken-in versus tested new. Some characteristics may stabilize when pre-tested a number of times.

The next article will be:

**Intro to MSA of Continuous Data – Part 7: R&R using Wheeler’s Honest Gage Study**
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