Calibration and Monitoring Boards
The HCAL calibration relies on the calibration and monitoring board (CMB). Each module is connected to one CMB, housing twelve LEDs and twelve PIN-diodes. In addition each CMB houses two temperature sensors. Five more temperature sensors are distributed across each module.
The light of each LED is distributed via a bundle of 19 clear light guiding fibers with 0.75mm diameter. These fibers are glued together in a metal sleeve, which is centered in front of the LED. 18 fibers are coupled to scintillating tiles via mirror caps, the core fiber of each bundle is coupled via a special connector to a PIN-diode to monitor the LED amplitude. The light intensity spread between the fibers of one bundle are tuned to be below a factor of two between brightest and dimmest fiber.
Some more information about the commissioning of the calibration and monitoring board is given in my diploma thesis
More on the HCAL calibration