The sound of sorting

Howard Shapiro hms at
Fri Mar 5 15:18:58 EST 2004

Cris Bare wrote-

>On my bus ride in from New Jersey this morning, I was, as I often do, 
>pondering the intricacies of the jet-in-air sorter -- voltages, rates, and 
>frequencies, when, as I often do, I wandered between subjects. I got to 
>thinking about the 48KHz piezo drop drive I had worked with previously, 
>and was struck by the similarity to my dabblings as an audio engineer.
>I wondered if anyone has ever brought in a meter and measured audio 
>frequencies and power generated by a sorter running full blast
>It is certainly not quiet environment.  I know that I rely upon my ears 
>during a sort for many clues about status: arcing electrodes, clogged 
>nozzles, failed hard drives, full waste vessel alarms.    But I also 
>wondered how all those soundwaves have affected my ears.  My wife will 
>certainly attest that I should have a gramophone bell at the 
>ready.  Whether this is related to occupational exposure, or a 
>rock-and-roll lifestyle is arguable.

When we sort with Cytomutts, which have a nominal 150 um orifice diameter, 
we typically use a 10 kHz drop drive frequency. The noise is audible. 
However, the transducer drive in our instruments, and in at least some 
commercial systems, is generated by an op amp, with maximum voltage output 
+/- 10 V and maximum current output about 25 mA, so the audio power at the 
drop drive frequency couldn't be more than a couple of tenths of a watt. At 
higher frequencies, sound gets more directional, and is thus more likely to 
be blocked by various hardware components getting between the transducer 
and the operator's ear, leading me to suspect that other sources of ambient 
noise may be more likely to damage hearing over long periods of time. Of 
course, I could be persuaded by evidence to the contrary.


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