Measurement Terms

Accuracy

 What is "Measurement Accuracy"?

Measurement accuracy, or just accuracy, represents the closeness of measured values to true values.  Accuracy is the general term used to describe the specified limits of measurement error for a given measuring instrument. The specified accuracy may include tolerance limits or maximum permissible errors.

Accuracy specifications sometimes use formulas. For example, an accuracy specification for the length measurement error for some measuring instrument, might involve using a maximum permissible error (MPE) formula that looks like the following:

MPE = 1.7+3L/1000 μm        L = measured length (mm)

The MPE is the specified limit of error, or accuracy, across the instrument measuring range as show in Figure 1.

Figure 1.

Determining the Specified Accuracy for a Measured Length

• The specified accuracy is calculated by substituting the actual measured length into a mathematical formula (Figure 2).
  
  MPE =1.7+3 L/1,000 (μm)        L= measured length (mm)

  
  i.e. (1): When measuring a length of 50 mm ・・・
               MPE =1.7+3×50/1, 000=1.85 μm

  
  i.e. (2): When measuring a length of 500 mm ・・・
               MPE =1.7+3×500/1,000=3.2 μm

Figure 2.

Key Considerations

When comparing the accuracy of measuring instruments, calculate not only the initial term.

(1.7 μm in the above example) but also the contribution from the measured length. For comparison please review (Figure 3.).

i.e.①：MPE =1.7+3 L/1,000 (μm)        L= measured length (mm)

           →MPE =4.7 μm when measuring 1,000 mm

i.e.②： MPE =0.7+5 L/1,000 (μm)        L= measured length (mm)

           →MPE =5.7 μm when measuring 1,000 mm

 Figure 3. 

Need help solving a measurement problem? Contact us anytime!

Related Solutions and Applications

FORMTRACER Avant C Series - Contour Measuring Machine

The FORMTRACER Avant C simplifies setup and alignment to reduce workpiece securing time and can be easily converted into a surface roughness measuring instrument with a retrofit detector.

QV Apex Pro Series - CNC Vision Measuring Machine

The QV APEX Pro CNC Vision Measuring Systems feature the advanced StrobeSnap function and synchronized camera-strobe light operation, enabling high-speed, non-stop measurements with up to 45% reduced measurement time compared to previous models.  

CRYSTA-Apex V - General-Purpose CNC Coordinate Measuring Machine

The CRYSTA-Apex V is a standard accuracy, high-speed CNC coordinate measuring machine designed for versatile dimensional and geometric tolerance measurements, offering improved productivity and enhanced visualization within a single unit.