Required outputs included power data, which was determined from the rotational velocity of the shaft and the torque on the shaft.  Other values to be determined included the velocity of the carriage, so that the flow rate, i.e. the velocity of the fluid flow across the turbine, was known.  Lastly, the drag on the system was to be found as a comparable design factor.

The velocity of the carriage was determined by clocking it at speed. Originally, an encoder was to be attached to the drive shaft of the tow tank carriage, but due to the data acquisition location, this was not an easily obtainable option.  The shaft torque was determined using an S type load cell as part of the gimbal/motor system discussed in the mechanical design section.  The angular velocity of the shaft was measured using an in-line rotary encoder connected to the upper shaft.  Finally, the drag force was measured by tensioning a second S type load cell with one end connected to a fixed point and the other connected to the free-floating upper plate of the apparatus.

Converting the raw data from the instruments into a useful form on a computer was a process which involved several intermediate devices.  The load cells have one output that is on the order of tens of millivolts, whereas the encoder provides an output that is a frequency (alternating values of fixed voltage output which switch back and forth at a speed which is related to the rate at which the encoder shaft is rotating).  The team decided to normalize these different output signals using signal conditioners (connected to an isolation module mounting rack) so that all of them were between 0 and 5 V.  This voltage range matched that of an available data acquisition system (DAQ) used this as an acceptable range for its incoming signals.  The DAQ is able to handle up to eight analog and eight digital channels in real time, making only one USB connection to a computer necessary to transfer over all of the data.  For the project only three analog channels were used, but the extra channels allow for the possibility of more data signals in the future, perhaps if array effects are studied. 

With useful signals reaching the computer, a computer program called LabVIEW was used to interface with the DAQ. The program LabVIEW was used to collect the data samples and to write them to file.  It was also capable of pre processing the data into units of measure if desired, however this capability was not used.

HARDWARE SPECIFICATIONS

The major piece of electronic hardware used was the DAQ PMD 1608-FS, which allowed for 16 total channels of information to be input and a tremendous sampling rate, allowing for very accurate readings.  This was used by a former project allowing us to save money by not purchasing a new DAQ.  The voltage signals read by the DAQ were from a voltage conditioning source known as an isolation module mounting rack.  The model used was an ISO-Rack08, which could hold up to 8 cartridges.  The conditioner used was a frequency to voltage card with a range of 0 to 1000 Hz and an output of 0 to 5 V.  The other two conditioners were for the load cells and had an input of +/-100mV and +/-30mV, with an output range of 0 to 5 V.  The encoder was a TRD-N100-RZWD (Totem pole), and the load cells were Massload S type ML-0200’s of 100 and 50 lb capacity.  A seal able hard plastic box protects much of the wiring and more sensitive equipment from the harsh water environment of the tow tank facility.  The components inside the box were attached to a Plexiglas board to keep them from moving.   The box was mounted on a wooden frame that was bolted to the carriage.  This setup ensured a water-tight and secure environment for the vital electronic equipment.  Further specifications for the equipment can be seen below in Table XX.  Signal conditioning cards were manufactured by Dataforth Corporation¹ and DATAQ Instruments²

Signal Conditioning Card Specifications

Wiring Diagram