The 2MHz Metrology is used to determine the exact position of mirror systems which can be moved a linear rail of 35m called the Fast Delay Line. The FDL control system is very complex and requires a position feedback of +-2nm. The position is sampled with a sample rate ranging from 4kHz to 10kHz.
The Metrology system received a 2MHz modulated digital signal from each of the six signal channel and one reference channel (see Laser Detector). A high-speed FPGA handles the phase-detection of the signal with a timing resolution of +-2ns. It is not simply possible to use a very high frequency zero-crossing sampling (GHz range) due to frequency constraints and resolution requirements. Therefore, another means were used to achieve such requirements.
Data is finally dumped into a PC via a high speed 16bit DMA card. This system can be controlled remotely via an Ethernet interface. Magnetic high resolution Hall sensors are used to determine a zero position along a FDL line.