The Calibration of Displacement Sensors Displacement measuring sensors play an essential role in all aspects of dimensional metrology. They can be used for direct displacement measurements but more often they are part of a measurement system, such as an atomic force microscope, roughness tester or a coordinate measuring machine (CMM). In order to achieve traceable measurements that can be related to the meter, these sensors must be calibrated against a reference standard that is more noise and errorfree than the sensor under test. A description of the various methods to achieve the ultimate traceability, repeatability and accuracy of such a calibration system is the main part of this paper. Various interferometric methods will be reviewed including several methods that use directly a primary standard as a reference: either an iodinestabilized laser or a frequency comb. It is shown that various methods exist to quantify or mitigate the periodic errors that are inherent to interferometric methods. Also it is shown that knowledge of this periodicity may lead to a separation of periodic and nonperiodic nonlinearity errors of both the calibration instrument as the sensor under test. This review is limited to smallrange sensors, typically with a range u003c100 xcexbcm. It is concluded that todayxe2x80x99s technology enables sound and traceable sensor calibration up to the subnano and even picometer level of uncertainties

A High Precision Time Grating Displacement Sensor Based on Temporal and Spatial Modulation of LightField A new displacement sensor with lightfield modulation, named as time grating, was proposed in this study. The purpose of this study was to reduce the reliance on highprecision measurements on highprecision manufacturing. The proposed sensor uses a light source to produce an alternative lightfield simultaneously for four groups of sinusoidal light transmission surfaces. Using the four orthogonally alternative lightfields as the carrier to synthesize a traveling wave signal which makes the object movement in the spatial proportion to the signal phase shift in the time, the moving displacement of the object can be measured by counting time pulses. The influence of the lightfield distribution on sensor measurement error was analyzed in detail. Aimed to reduce these influences, an optimization method that used continuous cosinusoidal light transmission surfaces with spatially symmetrical distribution was proposed, and the effectiveness of this method was verified with simulations and experiments. Experimental results demonstrated that the measurement accuracy reached 0.64 xcexbcm, within the range of 500 mm, with 0.6 mm pitch. Therefore, the lightfield time grating can achieve high precision measurement with a low cost and submillimeter period sensing unit.