Ultrasonic leak detecting apparatus

A method of detecting ultrasonic energy comprising the steps of:

• converting the ultrasonic energy into an electrical signal related to the intensity and frequency of the ultrasonic energy;
• amplifying said electrical signal with a high gain preamplifier;
• converting said amplified signal into an audio frequency signal related in magnitude and frequency to the attenuated signal by:
• a. commutating a high frequency switching signal with said preamplified signal to produce a pair of commutated signals;
• b. differentially filtering said commutated signals with a balanced audio frequency filter to provide a pair of balanced filter signals;
• and
• c. amplifying the balanced filtered signals in an audio amplifier having high common mode rejection to produce an audio frequency signal;
• and
• indicating the magnitude of the amplified audio frequency signal.

A frequency shift circuit for use in an ultrasonic detector which receives an electrical signal in the ultrasonic frequency range related to the intensity and frequency of ultrasonic energy received by an ultrasonic transducer and produces an audio frequency range signal related in magnitude and frequency to the received ultrasonic frequency range signal but shifted to an audio frequency range, said frequency shift circuit comprising:

• an oscillator which generates a switching signal;
• first and second comparators each having inverting and non-inverting inputs, said switching signal being applied to the inverting input of said first comparator and the non-inverting input of said second comparator and a reference voltage being applied to the non-inverting input of said first comparator and the inverting input of said second comparator;
• and
• a balanced audio frequency filter with two signal inputs, two comparator inputs and an output, the received ultrasonic frequency range signal being applied to both filter signal inputs and the comparator outputs being applied to respective filter comparator inputs, said balanced audio frequency filter providing said audio frequency range signal in said filter output.

An ultrasonic detector comprising:

• an ultrasonic transducer which produces an electrical output signal in the ultrasonic frequency range which is related to the intensity and frequency of received ultrasonic energy;
• a logarithmic attenuator having a plurality of substantially equal logarithmic attenuation steps, said attenuator receiving said ultrasonic frequency range signal and creating an attenuated signal;
• a selectively operable focusing probe that receives said ultrasonic energy and funnels it to the transducer, wherein said probe provides a signal gain magnitude substantially corresponding to the level of attenuation of one or more of said logarithmic attenuation steps;
• and
• a logarithmic signal level indicator receiving the attenuated signal and providing an indication of the magnitude of the attenuated signal.

An ultrasonic detector comprising:

• an ultrasonic transducer which produces an electrical output signal in the ultrasonic frequency range which is related to the intensity and frequency of received ultrasonic energy;
• a preamplifier connected to said transducer and generating an amplified version of the transducer electrical output signal;
• a frequency shift circuit receiving the output of the preamplifier and producing an audio frequency range signal related in magnitude and frequency to the received preamplified signal but shifted from the ultrasonic frequency range to an audio frequency range, said frequency shift circuit comprising:
• an oscillator which generates a switching signal;
• first and second comparators each having inverting and non-inverting inputs, said switching signal being applied to the inverting input of said first comparator and the non-inverting input of said second comparator and a reference voltage being applied to the non-inverting input of said first comparator and the inverting input of said second comparator;
• and
• a balanced audio frequency filter with two signal inputs, two switched signal inputs and a filter output, the received preamplified signal being applied to said filter signal inputs and the outputs of said comparators being applied to respective switched signal inputs;
• an audio amplifier which receives an audio frequency signal from the filter output of said frequency shift circuit and amplifies the audio frequency signal to create an amplified audio output signal;
• and
• a signal level indicator receiving the amplified audio output signal and providing an indication of the magnitude of the amplified audio output signal of the audio amplifier.

An ultrasonic detector comprising:

• an ultrasonic transducer which produces an electrical output signal in the ultrasonic frequency range which is related to the intensity and frequency of received ultrasonic energy;
• a high gain charge preamplifier connected to said transducer and generating an amplified version of the transducer electrical output signal;
• a multi-level logarithmic attenuator receiving the output of the preamplifier and creating an attenuated version of the output signal of said preamplifier, said logarithmic attenuator comprising:
• eight resistances connected in series between the logarithmic attenuator input and a reference level, and
• a multi-position switch with inputs connected to the logarithmic attenuator input and the junction of the resistances respectively, the wiper of the switch being connected to the output of the logarithmic attenuator, the values of the resistances being such that the output of the logarithmic attenuator is related to the preamplifier output and logarithmic attenuations thereof in seven fixed 10 dB steps;
• a frequency shift circuit connected to receive the output of the logarithmic attenuator and producing an audio frequency range signal related in magnitude and frequency to the attenuated signal, but shifted from the ultrasonic frequency range to an audio frequency range;
• an audio amplifier which receives the audio signal from the frequency shift circuit and amplifies the audio signal to create an amplified audio output signal;
• and
• a signal level indicator receiving the amplified audio output signal and providing an indication of the magnitude of the amplified audio output signal of the audio amplifier.