Understanding Acceptance Standards for Touch Probe CMMs

In the Coordinate Measuring Machine (CMM) Industry, it is important to understand and how performance is measured and certified. Two of the most widely used acceptance standards with touch probes sensors are:

1. EN BS ISO 10360-2:2001 – Used for older legacy machines.
2. EN BS ISO 10360-2:2009 – Current latest standard.

These standards define how to verify a CMM’s accuracy and outline how calibration uncertainty is factored into the machine’s specification.

Why Do Acceptance Standards Matter?

Acceptance standards allow you to verify a CMM’s measurement accuracy under real-world conditions, make consistent comparisons across different machines and manufacturers, and understand how calibration uncertainty can affect results. When choosing a CMM, referencing the relevant standard ensures you have a clear understanding of how the machine’s performance is being measured. 

Key Difference : Calibration Uncertainty

The biggest distinction between the 2001 and 2009 versions lies in how calibration uncertainty is accounted for: 

• ISO 10360-2:2001 
  • Includes a statement about calibration uncertainty on the certificate. 
  • It is a simpler approach common in older machines. 

• ISO 10360-2:2009 
  • Incorporates the uncertainty calculation directly into the machine’s specification. 
  • Offers a more integrated and transparent method, reflecting modern best practices. 

This extra step in the 2009 standard provides additional confidence for customers, ensuring that all potential sources of error, such as calibration equipment, environmental factors, and machine performance are factored into the final specification. 

What Does “Best Case Uncertainty” Look Like?

An example of a “best case uncertainty” specification might be expressed as: 

1.3 + (2.5 length in m) um this equates to a machine specification of:  

E_oMPE=A_o + L/K_o or  E_oMPE=1.3 + L/400 Which means according to ISO 10360-2:2009 a machine with this specification can have no errors @ 20^oC, this is not going to happen even with the best will in the world. 

To sum up please see an example of the 2001 compared to 2009 specification. 

E_oMPE =  1.4 + L/400 (EN BS ISO 10360-2:2001@ 20^oC) 

E_oMPE = 2.7 + L/200 (EN BS ISO 10360-2:2009@ 20^oC) 

This formula suggests that, at 20°C and under perfect conditions, the machine would have essentially zero measurement error. Perfect conditions are difficult to achieve, so there must be a small margin of tolerance to reflect actual operating environments. 

You’ll notice that the 2009 standard’s formula generally looks larger. This is because it integrates the uncertainty budget into the specification, providing a more realistic measurement of what the machine can achieve in everyday use. 

Bringing It All Together

While these technical details may seem complex, they’re crucial for accurately comparing CMMs. By clarifying which acceptance standard are used, and how uncertainty factors into the machine’s specification, you can have more confidence in choosing the right equipment. 

Pro Tip: Consider creating a spreadsheet or calculator to quickly convert between the two standards.  

Ready to Learn More

If you have any questions about acceptance standards, how to interpret machine specifications, or how to ensure your CMM is operating at peak performance, we can help. Our technical team is here to help you navigate the intricacies of ISO 10360-2 whether you’re working with legacy machines or the latest, high-precision models.