Hydrophone calibrator

Claim 2

A hydrophone testing apparatus comprising: chamber means having a cylindrically shaped interior cavity for receiving the hydrophone to be tested, and adapted to be filled with a liquid, and having an inner cylindrical wall bounding said cavity a first cylindrical tube of piezo-ceramic material forming part of said inner wall and extending about said cavity for imparting sound to said liquid, a second cylindrical tube of piezo-ceramic material forming part of said inner wall and extending about said cavity axially aligned with said first tube for receiving the sound imparted to said liquid by said first tube, and producing a first electrical signal, means for producing a second electrical signal from the sound received by said hydrophone being tested and means for comparing said first and second electrical signals to test said hydrophone.

Claim 3

Apparatus as in claim 1 including means for shielding the ends of said tubes.

Claim 4

An apparatus as in claim 1 wherein said liquid is water.

Claim 5

An apparatus as in claim 1 including means for producing a step change of pressure in said chamber means to calibrate said second tube.

Claim 6

An apparatus as in claim 4 wherein said producing means includes a first and second manometer having a given differential level and valve means for switching the liquid in said chamber means from one manometer to the other manometer to produce said step change.

Claim 7

An apparatus as in claim 5 wherein said given level is 10 centimeters and said step change is 10,000 microbars.

Claim 8

Apparatus as in claim 1 wherein said comparing means includes means for producing a signal which is a function of the ratio of said first and second signals.

Claim 9

Apparatus as in claim 1 wherein said comparing means includes a first peak detector for receiving said first signal, a first logarithmic amplifier for receiving the output of said first peak detector and producing a third signal, a second peak detector for receiving said second signal, a second logarithmic amplifier for receiving the output of said second peak detector and producing a fourth signal, and a summing amplifier for receiving said third and fourth signals and producing a fifth signal which is a function of the ratio of said first and second signals.

Claim 10

Apparatus as in claim 8 including a D.C. meter for displaying said fifth signal.

Claim 11

Apparatus as in claim 1 wherein said comparing means includes means for determining the sensitivity of said hydrophone.

Claim 12

An apparatus as in claim 1 including oscillator means connected to said first tube for causing said tube to impart said sound to said liquid.

Claim 13

An apparatus as in claim 11 including means to vary the frequency of said oscillator.

Claim 14

A hydrophone testing apparatus comprising: chamber means having a cylindrically shaped interior cavity for receiving the hydrophone to be tested and adapted to be filled with a liquid and having an inner cylindrical wall bounding said cavity, a first cylindrical tube of piezo-ceramic material forming part of said inner wall and extending about said cavity for imparting acoustical vibrations to said liquid, a second tube of piezo-ceramic material forming part of said inner wall and extending about said cavity axially aligned with said first tube for receiving the sound imparted to said liquid by said first tube and producing a first electrical signal, variable oscillator means connected to said first tube for causing said first tube impart said vibrations to said liquid, means for producing a second electrical signal from the vibrations received from said liquid by said hydrophone, means for calibrating said second tube by applying a step change in pressure to said liquid, and means for producing a signal from said first and Second signals which is a function of the ratio of said first and second signals.

Claim 15

A hydrophone testing apparatus comprising: chamber means having a cylindrically shaped interior cavity for receiving the hydrophone to be tested and adapted to be filled with a liquid and having an inner cylindrical wall bounding said cavity, a first cylindrical tube of piezo-ceramic material forming part of said inner wall and extending about said cavity for imparting acoustical vibrations to said liquid, a second tube of piezo-ceramic material forming part of said inner wall and extending about said cavity axially aligned with said first tube for receiving the sound imparted to said liquid by said first tube and producing a first electrical signal, variable oscillator means connected to said first tube for causing said first tube impart said vibrations to said liquid, means for producing a second electrical signal from the vibrations received from said liquid by said hydrophone, means for calibrating said second tube by applying a step change in pressure to said liquid, and means for producing a signal from said first and Second signals which is a function of the ratio of said first and second signals.

Claim 18

A method as in claim 14 including the steps of calibrating said second hydrophone by applying a step change in pressure to said liquid.

Claim 19

A method as in claim 14 including the step of varying the frequency of the signal driving said first tube so as to obtain the sensitivity of said hydrophone over a given frequency range.

Claim 20

A method as in claim 14 wherein said step of comparing includes the step of producing an electrical signal which is a function of the ratio of said signals produced by said hydrophone and said signals produced by said second tube.

Claim 21

A method as in claim 17 wherein said step of producing includes the steps of applying the signals produced by said hydrophone to a first peak detector, applying the output of said first peak detector to a first logarithmic amplifier, applying the signals produced by said second tube to a second peak detector, applying the output of said second peak detector to a second logarithmic amplifier, and applying the outputs of said first and second logarithmic amplifiers to a summing amplifier to produce a signal which is a function of the ratio of the signals from said hydrophone and the signals from said second ring.