[ this is a copy of a private request by a individual with a similar need, doppler DIY ... see also:
http://www.scubaboard.com/showthread.php?p=498600&highlight=doppler#post498600
Good luck, and please post your results for us to examine ...]
At 11:26 PM 2/19/04 +0000, wrote:
Doppler is a good idea if you can find a good [robust and not a battery eater] cheap Doppler stethoscope, bubbling is not a 1:1 relationship with bends, but I'd like to know too, if the price point were under $200 I'd bite
While I think about it, you being a doc of the medical type, rather than of
the engineering type like myself, perhaps you could help me out.
my pleasure
Our group has been looking at purchasing a Doppler to test ourselves after
big dives and have identified a few options.
The cheapest is uni-directional, has 3 level waveform calibration, and only
an analogue audio output.
this is the typical device on the market, many DCI workers use a Mini Huntleigh Dopplex D900 5 MHZ probe in the $400-500 range. There are some no-name brands being sold for under $300, but I've no knowledge of its use.
The mid-price unit is bi-directional, has 5 level waveform calibration, and
only an analogue audio output.
The most expensive unit is bi-directional, has 5 level waveform calibration,
and has both analogue audio output and a ASCII data output stream via
RS-232.
For DCS type analysis do we need a bi-directional unit ?
not needed, FYI these types can be used to calculate flow forward and backward of the transducer, only necessary in quantifying blood flow
Is it worth paying the extra for a 5 level waveform calibration over a 3
level one ?
unnecessary , see below on calibration for DCS studies, you don't even need 3, you basically want an el cheapo doppler stethoscope with analog output that can be attached to a tape recorder
Since we are looking for the presence of bubbles which can be heard in the
audio outputs, is there anything extra or better that can be obtained from
not for DCI studies using bubbles
the ASCII data output stream , which I believe primarily contains velocity &
flow rate type of information ?
yes that's what its for and its not needed
Since we are spreading the cost between our group the price differential is
not that relevant, but clearly we don't want to be buying something that is
totally over the top.
Absolutely you don't need many. But food for thought: if you delay collecting data from some divers post dive, one guy could be bubbling greatly while you sequentially collect data from other team members, so this is a dilemma and its best by recording at intervals post dive.
Bubble grade calibration is subjective, so collecting too much data is moot. Also, field analysis is nearly useless, too much activity and extraneous noise, you are better off recording the analog output on a good tape recorder, then analyzing the sounds on your PC, including applying any filters to reduce ambient noise. You collect data at set intervals, 30,60, 90, min post dive, and trim or add time based on that.
DCS study calibration are done to insure testers are trained by people who can trace their heritage to the inner circle of DCS workers in the USN and RN. That would be important if you want a study for medical publication, however, with constant use, you can detect bubbles as a change from ambient sounds easily without special training. However your grade 2 maybe some elses grade 3, for example, so in general use, its best to use two grade, low grade= 1 or 2, and high = grades 3 or 4. If you record it, you can always adjust your calibrations later on after someone with more experience hears the sounds and blesses your grades.
There a lot you can contribute that existing workers haven't done: human data. Further, with any el cheapo computer, you can use digital subtraction, which is not used in most recent DCI work, to reduce the ambient body noises easily without electronic filters.
On scubaboard.com or thedecostop.com, there is a user who frequently doppler's himself, Kendall Raine, maybe good to send him email. He can detail experience with field use of a doppler during dives.
