04 August 2015: Morteza Farmani

Many participants of our seminars on measurement system analysis and measurement uncertainty studies ask about the tolerance needed to apply specific measuring equipment.

Measuring equipment fulfilling various measuring tasks is referred to as standard measuring equipment. 30% to 90% of all measuring devices applied by automotive suppliers are considered to be standard measuring equipment. Typical examples are callipers, micrometers or dial gauges.

An important characteristic of standard measuring equipment is that it is produced and calibrated according to specified guidelines and standards. These documents specify the maximum permissible error at different measuring points; you must not exceed these limits in the production of standard measuring equipment.

In general, even measuring machines and other measurement systems (especially new ones) have a documented MPE which will be provided to you when you purchase the respective equipment.

Some measurement engineers apply the following rule of thumb even in practice – they consider measuring equipment capable of performing a specific task if the tolerance of the characteristic is at least ten times the measurement uncertainty (error limit) of the measurement system for this characteristic.

The so-called “golden rule of metrology” for the selection of appropriate standard measuring equipment states that the maximum permissible error (MPE) must not exceed 10% of the tolerance to be inspected.

The following examples compare the result of this golden rule with the results calculated according to the industry standard VDA 5, 2nd edition 2010. Nowadays, VDA volume 5 is widely accepted, even outside the automotive industry...