Measurement apparatus and method

A method for operating a measurement apparatus mounted within the enclosure of a machine, the measurement apparatus comprising (a) a measurement device that includes an optical tool-setting device having a transmitter for passing light to a receiver along an optical beam path into which a tool to be measured can be inserted and (b) a protection means for protecting the measurement device from contaminants present within the enclosure, the protection means being switchable between at least a first mode that protects the measurement device from contaminants and a second mode that provides less protection of the measurement device from contaminants than the first mode,

• wherein the method comprises the steps of:
• (i) sensing an amount of contamination within the enclosure, and
• (ii) determining when the protection means can adopt the second mode based on the amount of contamination sensed in step (i).

A measurement apparatus for mounting within an enclosure of a machine, comprising;

• a measurement device, and
• a shutter for protecting the measurement device from ingress of contaminants present within the enclosure, the shutter being switchable between at least a first mode that protects the measurement device from contaminants and a second mode that provides less protection of the measurement device from the ingress of contaminants than the first mode, the shutter providing a larger aperture in the second mode than in the first mode, wherein
• the apparatus comprises a contaminant sensor for sensing contamination within the enclosure, the sensed contamination being used to determine when the shutter can adopt the second mode.