Velocimeter probe alignment tips

We recently had inquiries on how to best align a Vectrino in a laboratory flume to ensure alignment of the coordinate systems. Here are the methods we have used to accomplish this, but please feel free to add any additional suggestions you've developed in your own laboratories.

1. For a quick setup aligning everything by eye works surprisingly well if you have good references to align against (flume walls are great for this!). 

2. For a more rigorous setup a post level (two spirit levels mounted orthogonal to one another: http://www.amazon.com/Johnson-Level-Tool-175-L-Post/dp/B0009WG3HI) can be used to make sure the mounting fixture and probe are level. This assumes the top of your flume is level since everything is usually mounted on a cross piece to it. If you have a tilting flume this method won't work. 

3. For a non-standard setup where the probe is horizontal instead of vertical or for side looking probes, a level of any type is needed to make sure the probe head parallel to the flume bottom or very accurate distance measurements.

4. Look at the probe check plot after mounting the probe and filling the flume with water. Tilts in the head can be identified there based on the return echo from the bottom (as long as the velocimeter can see the bottom). I look at the sharp front of the bottom echo and just make sure all the beams see it in the same location.

5. As far as rotation of the head, if you have a ruler with a wide enough surface, we use a level with markings on it's top, you can align the upstream and downstream probe pair at the same distance from one wall. It's also fairly easy to rotate the head once the flume is running and try to minimize the cross stream and vertical components (if this is how your flow is working).

6. I strongly recommend using zipties to mount the probe head as they will typically allow easier adjustment and are difficult to overtighten and cause damage to the probe head. The potted area is where I usually attach the head to my mount. I have seen damage to probe heads caused by u-bolt mounting setups.

7. If you're more math inclined and don't mind transforming your data, you can develop a minimization routine that will rotate and apply pitchs and rolls to the measured velocities to "level" the head by minimizing the appropriate components.

If you have any setups that have worked well please share pictures of them as well!

P.J.