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33 KHz Step Up transformer

Discussion in 'High Voltage' started by naumank, May 28, 2016.

  1. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    I don't know what medium you are using, but assume it is liquid or much lower impedanc than air.
    Impedance matching is critical on linear interfaces to avoid false echoes. If the ESR of your transducer does not match the ESR of the medium, then mechanical horns can amplify the pressure wave and transform the impedance by gain-squared to help in matching. Although cavitation may occur from excess power density at the interface and thus abrupt impedance rise, the impedance is largely newtonian mass vs pressure @f with the fluidic dampening like capacitance.

    To answer your question, I dont have the impulse response or burst F envelope response to determine your situation, but usually, mismatch at the exciter<>medium interface is always mismatched, so interface echoes will always exist which causes reflected current you do not want. By having a very low driver impedance, this echo current during Tx gets attenuated. Since the medium velocity of pressure is far lower than the electrical velocity at 2/3c , the electrical mismatch is less important than suppressing the mechanical interface echo. Thus you want an ideal voltage source, e.g. negative feedback source with gain reduced Impedance to suppress the mechanical echoes at the interface. Thus is why it is done with a dampening factor of load/source=100 to 1000 in high power woofers. Higher= better. Although you do not get maximum power transfer like in linear telephones, RF and microwave linear devices, you get minimum mechanical echo and distortion.

    Your objective is to make the best impedance match at the interface of the sensor. Rigid mount, with horn, then lowest impedance on source to suppress interface reflections.

    Impedance matching is normally done reactive loads using the complex conjugate.
     
    Last edited: May 29, 2016
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  2. naumank

    naumank Member

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    Hi Eric

    Is it possible for you to tell me what transducer you used and what was maximum depth achieved practically?

    Thanks
     
  3. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi nau,
    I have been trying to back track in finding the part numbers for the transducers.
    Problem is that I closed my company down in 2002, after 21 years of trading, as I was 70 years old.!
    About 10 years later, I destroyed or dumped all the company paper work and records [ I have kept all the hardware].

    The sounders at that time were made by Kelvin Hughes and Krupp Atlas.

    They were dual , 210kHz / 30kHz, 1kW, outer hull mounted 'shoe' styles.
    The 30kHz was capable of 1500 metres and the 200kHz was used down to 200/300 mtrs.
    Inshore navigation and dredging application.

    If I do find better details, I will post.

    E
     
  4. dave

    Dave New Member

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  5. naumank

    naumank Member

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    Hi Ericgibbs

    Thanks, i greatly appreciate your help and am eager to learn from your experience in future.
     
  6. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    In your situation the decaying piezo ringing will mask any short range echoes, it is necessary to keep your half bridge driver at 0V for an optimal (TBD) dwell time between end of burst and Rx enable.
     
  7. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi tony,
    This is known as the TX suppression period, which can be adjusted by the surveyor to suit the local conditions.
    TX Suppression is usually designed into the RX circuitry.

    E
     
  8. naumank

    naumank Member

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    Hi Tony Stewart & Ericgibbs

    Thanks for pointing out as i totally ignored it in my design. Is it possible to theoretically calculate "optimal (TBD) dwell time between end of burst and Rx enable" using the transducer parameters or it has to be observed practically depending on local conditions? Can a T/R switch be used to control it?
     
  9. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    I have found that it is better to provide the user with an adjustable TX suppression period.
    From say from zero thru 200mSec, this can been done best in the software or a triggered monostable which blocks the TX pulse as being recognised as a bottom echo before being Digitised.

    The echo display would normally show all the TX noise as well as any other signals, fish, weed, water density interfaces, this enables the user to correctly set up the Suppression, Acceptance Gating and any Depth Averaging.

    Do not forget the time swept gain requirement for the receiver.

    E
     

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