Do not try to download you sensus ultra under mac os yosemite.
I tried to do so, using macdive and the PL driver, and it failed. Yosemite made changes to serial ports. After doing some troubleshooting with Kris Wilks (and getting a new serial driver from him), it seemed like it was working but downloaded no data. From Kris:
I can't explain for sure why this happened, but my suspicion is that the improperly configured USB adapter may have put the recorder into a state in which it was consuming more power than usual. This could have allowed the battery voltage to droop (temporarily) low enough to trip the internal reset mechanism.
Unfortunately, the reboot process involves a memory test which wipes the contents of the device. So I'm afraid any data that you had not already downloaded is gone.
I hadn't downloaded since yosemite came out, and lost about 40 dives (not to mention the really old ones that never downloaded at all).
This new driver from Kris at Reefnet may be the fix and everything may now be fine, but if you have valuable data in your Sensus, leave it alone until this gets figured out.