Accurate measurement of displacement is essential for reliable dimensional metrology for both advanced manufacturing and research. One-dimensional contact probes and linear transducers are commonly used in applications such as gauge block comparators, precision positioning systems and industrial measurement equipment. Although these instruments can provide nanometre-level resolution, their accuracy needs to be ensured through traceable calibration.
When a linear transducer is used as a reference instrument for other less precise devices, such as dial gauges or gauge blocks, measurement uncertainty has a critical role. The uncertainty of the reference instrument propagates directly to the uncertainty of the calibrated instrument, setting a lower bound on the achievable calibration uncertainty. To meet increasing accuracy requirements VTT MIKES has developed a new interferometric calibration system for 1D probes.
The new VTT MIKES calibration setup is based on a laser interferometer as the reference instrument, providing direct traceability to the SI metre. Probe displacement is performed using a high-quality motorized stage, enabling precise and repeatable movement. It also allows automated measurement procedure and thus reduces user influence and improves accuracy by allowing efficient repeated measurements. The instrument was designed for easy microscope assisted adjustment of transducer to allow accurate Abbe and cosine error elimination.
The system’s capabilities were proved in the EURAMET.L-S31 comparison for 60 mm transducers, where it achieved excellent results. Following the successful comparison, a new CMC (Calibration and Measurement Capability) for 1D displacement transducers and actuators for VTT MIKES has been approved and published in the key comparison database (KCDB). A CMC defines a laboratory’s ability to perform a specific measurement. Under the CIPM Mutual Recognition Arrangement, National Metrology Institutes' CMCs are peer-reviewed and listed in the KCDB, confirming international equivalence of their measurement standards and calibration certificates.
Improved capabilities and key benefits
- State-of-art nanometre level calibration, uncertainty U = Q[13 nm; 4.0E-7L], where L is the measured length
- Automated measurements with excellent repeatability
- High-density measurement point spacing for detailed probe characterisation
- Efficient characterisation of a wide range of 1D probes and linear transducers.
Impact and outlook
Improved calibration accuracy enhances confidence in dimensional measurements and supports tighter uncertainty budgets in manufacturing and metrology. By providing traceable, high-accuracy calibration of linear transducers, the new system improves the reliability of measurements in many applications and laboratories. Automation keeps the calibration cost reasonable since no manual work is required after alignment of the device under test.
The calibration setup is operational, and further development work continues, focusing on extending the range of supported devices that can be calibrated using it.
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