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WIND MONITORING


HOW WILL MET MASTS OF THE FUTURE COLLECT THEIR DATA?


As remote sensing is maturing, met masts must enhance their strengths in order to provide measurements complimentary to those taken by SODAR and LIDAR. A key strength of met masts is precision – the ability to state ‘at this point in space, the windspeed is exactly this’, rather than ‘within this volume, the average windspeed is this.’


How can this ability be improved? Our own data management guru and senior instrumentation engineer at Chillwind, Thomas Chase, discusses advances in data collection methods.


CURRENT SITUATION


A met mast datalogger receives data from its instruments in a range of methods. Analogue voltages and currents are used, as are frequency signals and some serial signals.


Each of these has inherent strengths and weaknesses: analogue signals are simple to implement, but susceptible to interference, can be affected by the long wires necessary, and require stable circuitry for accuracy. Frequency signals offer a good combination of accuracy and simplicity, but don’t offer much scope for the transmission of more than a single value per wire.


A range of serial protocols are in use, and are essential with instruments like ultrasonic anemometers because of the sheer number of different parameters they can measure.


ADVANTAGES OF SERIAL FOR ALL INSTRUMENTS


Because serial communications are digital, they are unaffected by long leads. Properly designed and implemented, they are practically immune to noise, and error correction closes the gap between ‘practically’ and ‘totally’.


Besides from improved accuracy, what other advantages can we gain from using a serial communications bus for all instruments?


The answer goes beyond data to metadata. This ‘data about data’ provides a context for the data itself. For example, each instrument could send its data to the logger, packaged with its serial number, and the instrument’s current state of health.


Now measurement campaigns generally last beyond the life of an instrument, refurbishments are routine. Instruments that provide their metadata will eliminate programme changes, and that perennially awkward need to change calibrations in the logger synchronously with changing the instrument.


Given that each instrument will need an internal microprocessor to engage in serial communications, they will also have the capability to have their calibration values programmed in at the wind tunnel.


Imagine too, that a need has been recognised for an additional instrument – this new instrument can be mounted, power and data lines connected, and it will introduce itself to the logger which will then automatically start recording the data sent.


PROBLEMS TO OVERCOME Currently, the idea of a complete plug- and-play instrument set on a met mast has hurdles to overcome – first would be the definition of a standard protocol for instruments to handshake with the logger and send data and metadata.


Second is cost – the ideas posited here are technically feasible, and inspired by current technology in the automotive sector, but development of these instruments would take time and therefore money. In the end, this money spent will recoup itself via increased data assurance.


Chillwind Ltd


48


www.windenergynetwork.co.uk


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