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PICList Thread
'[PICLIST] Understanding Ultrasonic Transducer Spec'
2002\03\21@233834 by Donovan Parks


I am planning to purchase a Panasonic Ultrasonic receiver and transmitter, but am having some trouble understanding the data sheet.

Specifically, the transmitter has a sound pressure level (SPL) of 112dB re 2*10^-5 Pa (that is, 0dB=2*10-5 Pa).  The receiver has a sensitivity of -45dB re 1V/Pa.

Assuming the devices are ideal and I loss no signal strength between the transmitter and receiver is the following correct.

112dB = 10^(112/20)*(2*10^-5Pa) = 7.96 Pa

So, the output of the receiver is:
   -45dB = 10^(-45/20)*1V/Pa = 0.0056 V/Pa
   7.96 Pa * 0.0056 V/Pa = 0.044 V

This just doesn't seem right as this would mean a receiver with a sensitivity of -90dB would have an output of 2.5*10-4V.  More expensive receivers have a larger absolute value for their sensitivity so I must be looking at this incorrectly.

Where am I going wrong? (Am I doing any of this right!)

Donovan Parks

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