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Data Acquisition Technology

The data acquisition process is clearly critical to a successful condition monitoring programme. Consequently, it is essential that the data acquisition hardware functions flawlessly at all times. For wind turbine applications, the fact that units are installed at a remote and mostly inaccessible location, exposed to ambient conditions and required to operate continuously makes this issue even more acute.

The VCOM-W systems have been specifically designed to be both robust and highly flexible. A high degree of environmental isolation has been deliberately used in all components to ensure that the units remain unaffected by operational conditions. The data acquisition units also have a range of different interfaces built in, to facilitate the use of different types of instrumentation. Internal diagnostic functions are used to constantly check the correct working of the system, and the software incorporates a special fail-safe feature which means the units can recover even in the event of a system crash.

Low Speed Sensing

One of the unusual features of wind turbines is the very slow rotational speed of the rotor and main shaft assembly. On all but very small machines, this poses significant problems for conventional piezoelectric accelerometers, which have very limited response at these frequencies. Special low-frequency piezoelectric sensors are often used to compensate for this, but they are relatively expensive, and even then their performance is limited at very low speeds.

To overcome these issues, Ventech Systems has developed its own low-speed acceleration sensor. The device has a flat frequency response down to DC level (ie constant, static acceleration), and thus can take accurate measurements regardless of the turbine size and speed. It has sufficient sensitivity to measure the very low accelerations generated at rotor speeds, and is fully sealed against the environmental conditions in a wind turbine. The units are even relatively inexpensive, so provide a cost saving over the option of using low frequency piezoelectric devices.

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