Signal bandpass filter apparatus

Abstract

A signal bandpass filter apparatus is disclosed wherein a direct short circuit between input and output is prevented and the loss of the ground reference of the filter is detectable and fail-safe in operation.

We claim as our invention: 
     
       1. In a signal bandpass filter apparatus operative with an input signal having a predetermined frequency and a load device, the combination of: first means responsive to said input signal for providing a first electrical to mechanical energy conversion;   second means operative with said first means for providing a second mechanical to electrical energy conversion;   third means operative with said second means for providing an output signal to said load device; and   fourth means connected to .[.supply a direct current.]. .Iadd.control the passage of said input signal to said load device and including an integrity checking .Iaddend.voltage signal .Iadd.provided .Iaddend.through said first means and through said second means for determining the operational integrity of said apparatus by disabling the passage of said input signal to said load device when a predetermined failure of said apparatus occurs .Iadd.with said integrity checking voltage signal being different than said input signal.Iaddend..   
     
     
       2. The apparatus of claim 1, including electrical insulating means positioned between said first means and said second means. 
     
     
       3. The apparatus of claim 1, with said first means including a piezoelectric transducer operative with a physically resonant member having a predetermined resonant characteristic in relation to the frequency of said input signal. 
     
     
       4. The apparatus of claim 1, with said first means including a first piezoelectric transducer operative with a first physically resonant member, with said second means including a second physically resonant member operative with a second piezoelectric transducer. 
     
     
       5. The apparatus of claim 1, including fifth means operative with said first means and said second means for physically coupling energy from said first means to said second means. 
     
     
       6. In a signal bandpass filter apparatus for passing an input electrical signal having a predetermined frequency to a load, the combination of: first means responsive to said input electrical signal and including a first piezoelectric transducer operative with a first mechanical member resonant at said frequency;   second means coupled with said first means for providing an output electrical signal to said load and including a second piezoelectric transducer operative with a second mechanical member resonant at said frequency; and   third means connected to each of said first means and said second means and providing .[.a direct current.]. .Iadd.an integrity voltage .Iaddend.signal through each of said first and second means for determining the integrity of said apparatus by controlling the passage of said input electrical signal to said load.Iadd., with said integrity signal being different than said input signal.Iaddend..   
     
     
       7. The apparatus of claim 6, with said third means providing a direct current voltage signal continuously through each of said first means and said second means for determining said integrity by disabling the passage of said input electrical signal to said load upon the occurrence of a predetermined failure of said apparatus. .Iadd. 8. In a signal bandpass filter apparatus operative with an input signal having a predetermined frequency and a load device, the combination of: first means including an input piezoelectric member and a first resonant member and responsive to said input signal for providing a first electrical to mechanical energy conversion;   second means including an output piezoelectric member and a second resonant member and operative with said first means for providing a second mechanical to electrical energy conversion;   third means operative with each of said first means and said second means for controlling the passage of the input signal to said load device by providing an integrity signal through each of the first means and the second means, with the integrity signal having a different frequency than the input signal;   fourth means positioned between said first means and said second means, with said fourth means separating said input resonant member from said output resonant member,   input connection means coupling the input signal to the input piezoelectric member and having a first length to determine that the input connection means cannot break to couple the input signal to the first resonant member, and   output connection means coupling the load device to the output piezoelectric member and having a second length to determine that the output connection means cannot break to couple the load device to the   
     
     
        second resonant member. .Iaddend. .Iadd. 9.  The signal bandpass filter apparatus of claim 8, with said fourth means comprising an electrical insulating member. .Iaddend.