Boston CCD Angle Monitor (BCAM)
 Figure: A Black H-BCAM. We see the front camera lens in a brass holder. On either side are two laser diodes, turned on. Above and below are the four white LEDs, turned off. |
A Boston CCD Angle Monitor (BCAM) is a simple, rugged, metrology instrument designed to monitor the geometry of large structures. A single-ended BCAM contains a camera and two light sources. The camera consists of a lens and an image sensor. The light sources are red laser diodes placed on either side of the lens. The laser diodes have no collimating lenses, and so act as point sources. A double-ended BCAM contains two cameras looking in opposite directions, with two pairs of light sources. One model of BCAM, the H-BCAM, adds an array of four white LEDs around each of its two camera lenses in addition to its laser diodes. Each BCAM uses its camera to monitor lasers on all other BCAMs and metrology sources in its field of view. The camera measures the position of each light source image on its image sensor. Calibration of the camera with respect to its kinematic mounting balls allows us to convert a point on the image sensor into a line in global coordinates upon which the point source should lie. A BCAM camera measures the bearing of sources with 50 μrad absolute accuracy and 5 μrad relative accuracy. It can operate with sources as near as 50 cm and as far as 50 m. Thousands of BCAMs are installed in High Energy Physics (HEP) particle detectors, such as the ATLAS End-Cap Muon Spectrometer Alignment Sytes, the ALICE Geometric Monitoring System, and other systems at CERN, Fermilab, and other national laboratories. The BCAM is an example of a LWDAQ Device. We read them out with LWDAQ Multiplexers, LWDAQ Cables, and LWDAQ Drivers. |