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Safety sensor for wind power

The safety vibration sensor NVA115 from TWK has been developed to protect wind power plants from damage caused by oscillations and vibrations. Data output is carried out via the CANopen interface.

The sensor completes TWK's portfolio of industrially SIL2-certified inclinometers, rotary encoders, and switching cam encoders (Photo: TWK)

The safety vibration sensor NVA115/S3 complies with SIL2 / PLd status and registers oscillations from 0,1 Hz to 100 Hz up to an amplitude of 2 g. It has been optimized for use in the wind power industry in order to protect wind power plants from damage caused by oscillations and vibrations. The sensor measures and evaluates vibrations in the mast head. The device consists of an acceleration sensor, a controller unit and three types of output interface. The main feature is two safety switching contacts (potential-free), which can be used e.g. in the safety chain to undertake safety shut-off in the event of excessively high acceleration values.

The measured value is evaluated using adjustable frequency filters and is supplied to the three different interfaces: two analog outputs, e.g. for the X and Y axis, CANopen (Safety) interface for safe data transfer plus two safe switching contacts for the safety chain, which interrupt the latter in the event that limit values are exceeded. Data output is carried out via the CANopen interface. The standard or the safety profile can be selected.

The measured acceleration can be output and further processed as a momentary or peak value, as an RMS mean value or now also as an integrated value. The latter function is important to shut off the system if an adjustable acceleration limit value is exceeded slightly but over a long period of time. The Fourier frequency analysis, which determines the frequency spectrum, rounds off the diverse functions offered by the sensor.

Due to its resistance to vibration and shock, the sensor is suitable for use in areas with rough environmental conditions. Electrical connection is carried out using two or three connectors. After determining the steady component and scaling, the measured values supplied by the acceleration sensor are made available to the six filter units. The steady component arises as a result of installation which is not precisely horizontal, with the result that part of the earth's gravitational field would also be measured.

The offset which occurs in the measured vibration value curve (zero point shift) due to the steady component is determined by means of calculation (distribution of the positive and negative measured values around the zero point) and is subtracted. The pure alternating component is output within a matter of seconds. This calculation takes place continually. This function can be shut off in the factory. The filter units can be individually programmed in the filter characteristics for frequency selection in the factory (low pass or band pass). They can be assigned to axes x, y or z (in the case of x and y also to the resulting ones). The majority of parameters can be set using the CANopen interface.


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