Patent ID: 8314389

Claim:
A measuring instrument for measuring a workpiece, comprising: a housing comprising a ceiling, a floor, a first sidewall, a second sidewall substantially parallel to the first sidewall, the first and second sidewalls connecting the ceiling and the floor, and an operating window defined between the first sidewall and the second sidewall; a box received in the housing and suspended to the ceiling, the box comprising a first surface opposing the floor; a supporting member positioned on the floor and configured for supporting the workpiece; a scanning probe partially received in the box and opposing the supporting member; a plurality of infrared light emitting devices positioned on the first sidewall close to the operating window; a plurality of infrared light receiving devices positioned on the second sidewall, each of the infrared light receiving devices aligned with a corresponding infrared light emitting device, and configured for receiving infrared lights emitted by the corresponding infrared light emitting device; at least two light sources positioned on the first surface of the box; and a controller electrically coupled to the infrared light receiving devices and the at least two light sources, wherein when one of the infrared light receiving devices does not receive infrared lights emitted by the corresponding infrared light emitting device, the controller turns the at least two light sources on.