OCR Text |
Show recorder, until it rests on the zero line of the left- hand chart scale. At the tower junction box, connect the test meter ( ohmmeter mode) to the anemometer circuits of the cable ( terminals 1 and 2). At the power supply- calibration unit, turn the velocity switch ON. Adjust R-. until the meter reads 450 ohms. Next, disconnect the test meter, set the calibrator to about 1 volt output and connect to the terminals F+ and G- at the tower. At the recorder, connect the two wires with in- line fuse holders from the calibration unit to the wind speed terminals of the recorder ( these are the terminals for the right hand recorder channel). If the right hand recorder pen deflects part way across the chart, proceed. If not, and the pen deflects to the left, reverse the two wires to the recorder. Next, set the output of the anemometer calibrator to exactly 4.0 volts. When this has been confirmed between tower and recorder sites, the man at the recorder can then adjust R£ until the recorder pen deflects exactly to 100 mph on the chart. Readjust R. slightly if necessary to obtain proper deflection of the pen. When these adjustments are completed, use a wrench to tighten the lock nuts on R^ j and R£. The velocity calibration is now complete. Reconnect the anemometer wires at the tower junction box to give normal deflection of the wind speed recorder pen. The direction calibration also requires two men with communication between tower and recorder. In this case the man at the tower has to climb it and position himself where he can both swing the wind vane and operate his radio. Mechanically zero the direction ( right- hand) pen of the recorder. With the direction switch OFF, turn R* all the way counterclockwise and R^ all the way clockwise. Make sure the vane body is positioned with the white mark pointing east and point the vane parallel to the white mark ( at the vane resistor cross- over point). Connect the two direction wires with in- line fuses to the direction terminals ( for the left- hand channel) of the recorder and turn the direction switch ON. The left-hand recorder pen should deflect to the right; if it deflects to the left, reverse the wires to the recorder. Carefully adjust the vane position for minimum pen deflection ( adjust to low side of the cross- over point). If little pen deflection occurs, turn Ro until it deflects. Turn R^ until the pen returns to zero on the chart. This balances out the line resistance in the wind vane bridge circuit. Now swing the vane to the position of maximum pen deflection ( high side of cross- over point). Move the vane very slowly to achieve maximum pen deflection. Holding the vane in this position, adjust Ro until the pen reads full- scale on the chart. The direction calibration should now be complete. The directions on the chart, equally spaced from zero to full- scale, should now be East, 74 |