PIV system operation

This section describes the setup and operation of the ME department's LaVision high frame rate particle image velocimetry system on the tow carriage and YZ traverse.

Mounting frames

Laser mount

1. Square the laser and light arm mount, and attach the light arm.
2. Remove carriage decking panels. See Figure 1.
3. Attach the laser and light arm mount to the carriage.
4. Clamp in place and tighten turnbuckle for added rigidity.
5. Check squareness and adjust accordingly.

Camera mount

1. Square the camera mount and attach the camera rail and viewing sled.
2. Lower the camera mount into the water over the rear of the tow carriage before sliding into mounting rails.
3. Clamp the vertical supports of the camera mount to the rear face of the carriage.
4. Check squareness and adjust accordingly until viewing sled is in plane with water surface.

Mounting PIV equipment

1. Place chiller on the carriage and power with 240V/20A.
2. Attach the laser to its mounting frame.
3. Run the laser coolant lines to the chiller. Note: Blue marks the supply line from the chiller filter, while red marks the return line.
4. Verify the chiller water level by turning it on. Top off with distilled water if necessary.
5. Place the power supplies on the carriage and power each with 120V/15A.
6. Attach the laser power cables to the power supplies as labeled. Note: Power supplies are labeled 10-231.1 and 10-231.2. These will be henceforth referred to as the top and bottom power supplies, respectively.
7. Attach chiller flow sensor to top power supply.
8. Place the DAQ cube on the carriage and power with 120V/15A.
9. Place the Ethernet switch on the carriage and power with the data acquisition cube.
10. Connect the Ethernet switch to the data acquisition cube with the line in connected to the carriage Ethernet 2 port.
11. Connect any other measurement devices to the Ethernet switch (ADV, ADCP, etc.)
12. Run a power strip to the front of the carriage from one of the 120V/15A outlets.
13. Place the high speed controller on the carriage and power with the power strip.
14. Attach the laser cable from the high speed controller to the top and bottom power supplies as labeled.
15. Attach the Trigger Input “Trigger” line to the National Instruments TTL output using a BNC cable.
16. Attach the Port A “Pho 0” line to any externally triggered devices (ADV, ADCP, etc.) using a BNC cable.
17. Mount the camera to the bracket and slide the bracket onto the camera rail.
18. Center the camera over the viewing sled and level the camera.
19. Power the camera with the power strip.
20. Attach Port A on the high speed controller to the camera.
21. Attach the Ethernet switch to the camera.
22. Place the computer and monitor on the carriage and power with the data acquisition cube.
23. Connect the monitor to the computer’s DVI port.
24. Connect the mouse, keyboard, DaVis license dongle, and high speed controller to the computer’s USB ports.
25. Connect the Ethernet switch to the lower Ethernet port on the computer.

Starting the system

NOTE: Before operating a Class 4 laser, use proper PPE and follow all safety guidelines.

1. Turn on the tow system as per the instructions on the tow_tank:operation:tow_system page.
2. Turn on the data acquisition cube.
3. Turn on the computer and monitor and log in.
4. Turn on the chiller by hitting the switch in the back and then the button on the front.
5. The chiller should be programmed to 20°C and can be adjusted using the arrow buttons.
6. Remove the lens cap from the laser.
7. Remove the lens cap from the camera and turn on the camera.
8. Turn on the high speed controller.
9. Arm the laser by turning the keys on the power supplies to the right.
10. Turn the power supplies on using the red switches. A beep will sound.
11. Turn on the shutter and LDD for each laser being used (top only for single laser PIV, both for frame straddling). Note: Do not increase the amperage to the laser yet, and never cut power to the laser suddenly during use.
12. Start DaVis 8.05. Note: Once DaVis has initialized all of the equipment and verified the license, the system can be controlled via remote desktop from the tow platform. License verification cannot be performed via remote desktop.

Calibrating the System

Before operating a Class 4 laser, use proper PPE and follow all safety guidelines.

1. Enter the recording module in DaVis and switch the light source on to adjust mode.
2. On the power supplies, press the menu button and select the diode settings.
3. Select the amperage setting and slowly increase the intensity using the adjustment knob or arrow buttons until the light sheet is just visible.
4. Adjust the alignment of the mirror, yaw of the light arm, roll of the cylindrical lens, and focal length of the spherical lens to properly align, level, and focus the light sheet for the desired field of view. This is an iterative process.
5. With the light sheet illuminated, install the calibration plate.
6. Level the calibration plate in the light sheet by raising it until the plate is just illuminated on all four corners.
7. Turn down the amperage to the laser.
8. Begin “live mode” recording in DaVis and adjust the camera’s f-stop and focal length to obtain a calibration image that is everywhere focused and well illuminated, without saturating the CCD. //Note: Begin with the lowest f-stop to avoid damaging the camera CCD.//
9. Enter the calibration module in DaVis and follow the steps to obtain a calibration image.
10. Once calibrated, remove the calibration plate and make no further changes to the alignment of the camera or laser. Further adjustments to the focus of each may be necessary.