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LabVIEW 9 program is used to 1) control the water tunnel speed, 2) collect data from the UP Unit using GPIB interface and 3) control the traverse. The operating instructions for this LabVIEWg program is given in Appendix A. Calibration of Water Tunnel Velocity and Water Pressure Transducer

    The pitot-static probe remains fixed at the center of the air tunnel test section. Access to the air water interface is blocked by placing a plexiglas cover over the water tunnel. The block diagram for calibration is shown in Figure 3-6. Input voltage Va to the motor is increased in small intervals from 0 until a point where the dynamic head of the air stream is a little less than 2.5 in. of H20. For each Va, 25 readings are taken from Heise Gauge and also from UP 34970A DAQ unit over a period of approximately 10 seconds. Each of these 25 readings is averaged to get a single reading from the Heise Gauge and UP 34970A DAQ unit for that particular Va. The result recorded achieves the calibration of the P55D with respect to the Heise gauge.

    To calibrate the water tunnel velocity with respect to the motor frequency, the pitotstatic probe is positioned at the center of the water tunnel. The input voltage, v', to the pump motor is increased from 0-10 V DC in steps of 0.2 V. For each v, 25 readings are taken from the P55D using the UP 34970A DAQ unit over a period of approximately 10 seconds. Each of these 25 readings is averaged to get a single reading for a particular v, The result recorded achieves calibration of the water tunnel speed with the DAQ voltage input and is used for all measurements in future. This is shown in Figure 3-7. A look-up table for v, versus the motor frequency is recorded simultaneously to facilitate manual setting of desired speed based on frequency. The dependence is linear except at very low