Piezo Transducer Driver Circuit

Discussion in 'General Electronics Chat' started by h.yakub, Mar 11, 2019.

  1. h.yakub

    Thread Starter Member

    Mar 11, 2019
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    Hi,

    I am currently designing a driver circuit for Piezo transducer to measure liquid level of a closed sealed steel container. I have used 1 MHz Piezo transducer with a resistance of 5 ohms at resonant frequency, 30 mm diameter and a capacitance of 2200pF.
    The circuit works fine on plastic bottles and steel bottles, but the I am not able to get any echo on steel container.

    Can someone suggest few ideas that I can use to make it work on steel containers????????

    The circuit schematic that I am using currently is below.
    To simulate the driver circuit, please click on the multi-sim link:
    https://www.multisim.com/content/VZcYYdR4yB5RkaamevegJL/ultrasonic-transmitter/open/
    upload_2019-3-2_18-16-37.png
     
  2. ericgibbs

    Moderator

    Jan 29, 2010
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    hi h.y,
    Welcome to AAC.
    What range do you want to measure to a metal container, distance.?
    E
     
  3. h.yakub

    Thread Starter Member

    Mar 11, 2019
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    Hi ericgibbs,

    Thanks for your reply.

    The range of measurement is 1 cm - 38 cm, the diameter of metal container is 36 cm.

    The container is made up of a alloy material, not sure which alloy material.
     
  4. Yaakov

    Active Member

    Jan 27, 2019
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    How thick is the container wall? How thick were the test container walls?
     
  5. ericgibbs

    Moderator

    Jan 29, 2010
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    hi,
    This is a LTSpice simulation of your Transmit circuit.
    Please post a diagram of the Receiver.
    E
    Added:
    A slightly modified piezo load simulation showing the AC analysis
     
    Last edited: Mar 11, 2019
    h.yakub likes this.
  6. h.yakub

    Thread Starter Member

    Mar 11, 2019
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    Hi ericgibbs,

    I haven't design a receiver circuit yet. I am seeing the trigger and echo signals through oscilloscope.
     
  7. h.yakub

    Thread Starter Member

    Mar 11, 2019
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    Hi Yaakov,

    Thanks for your reply.

    The thickness of container wall is about 5mm - 7mm, and the test bottle thickness is of 2mm to 3mm.
     
  8. Yaakov

    Active Member

    Jan 27, 2019
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    Is it possible that the thicker wall is simply attenuating the signal to the point if can't be seen?
     
  9. h.yakub

    Thread Starter Member

    Mar 11, 2019
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    0
    Hi Yaakov,

    I have increased the power input as well to the piezo transducer, at the beginning I tested with 8 Watts of power, but then gradually increased the power to piezo transducer upto 60 Watts still, I am not able to see any Echo signal on the scope, whereas the transducer gives good amount of echo on Test bottles.
     
  10. Yaakov

    Active Member

    Jan 27, 2019
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    OK, then the other thing that comes to mind is the volume. Are they different?
     
  11. ericgibbs

    Moderator

    Jan 29, 2010
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    hi h,y,
    Please post details of the pulse period into the 2N7000.
    E
     
  12. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    2,228
    The shape of the container will affect the amount of ultrasonic energy reflected back to the transducer. Your test object should be the same shape, size and material as the items to be sensed.
     
  13. ericgibbs

    Moderator

    Jan 29, 2010
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    hi h.y,
    Please post details of the drive signal into the MOSFET Gate.
    On/Off periods.??

    E
     
  14. h.yakub

    Thread Starter Member

    Mar 11, 2019
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    0
    Hi ericgibbs,
    Sorry for replying late...
    The time period of pulses to Gate is 10 usecs, i.e, 10 pulses of 1 MHz at 5V and the OFF period is of 10 ms.
     
    Last edited: Mar 12, 2019
  15. h.yakub

    Thread Starter Member

    Mar 11, 2019
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    Yes, they are of different volumes, the test container is of shape of Steel bottle with 18 cm of height and 7 cm of width, with thickness of wall around 1~2 mm.
    The actual container is of 50 cm height, 36 cm width and wall thickness of ~5 mm. But what should I do to get echo on the actual container because, I have tried giving more power, using large diameter of piezo to increase echo sensitivity, but still not able to get any results.
     
    Last edited: Mar 12, 2019
  16. ericgibbs

    Moderator

    Jan 29, 2010
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    hi h.y,
    So the 1Mhz is a 50% High period ie: 0.5uSec.?
    Look at this option with a 30% High time, and modifications to the circuit.

    Do you have scope image you could post from the actual piezo test, on the bottle and the container.?
    E
     
  17. h.yakub

    Thread Starter Member

    Mar 11, 2019
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    Yes, the duty cycle is at 50%.
    The simulation results gives a Vp-p of around 60V, but when I connect the piezo it decreases to 12 Vp-p due to resistance of piezo i.e of 5 ohms at 1 MHz.
    Also, I have some scope images.
     
  18. ericgibbs

    Moderator

    Jan 29, 2010
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    hi,
    Do you have a datasheet for the piezo that you could post. 1R impedance seems low at 1MHz.
    Post an image showing the TX pulse and echo signal from a bottle also from the metal container.
    E

    BTW: expand the scope trace in the time axis, lets see the 10uS period
     
  19. h.yakub

    Thread Starter Member

    Mar 11, 2019
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    Yes, Please find the attachment of Images.
    1. One with Tx Pulse spread for 10 us time period
    2. Screenshot of datasheet (It is not an actual datasheet, but the factory can only
    provide these details to me,.)
    3. Tx pulse as well as echo signal, when tested on a plastic bottle
    PS : The screenshot Image may not be clear to see :p
     
  20. ericgibbs

    Moderator

    Jan 29, 2010
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    hi,
    Managed to read the Chinese d/s they say 3R impedance and 3600pF.
    Looking at the image of the 10uSec TX burst I would say that is not resonant.!
    Have you tried changing the 1MHz frequency around the 1MHz centre frequency.?
    Are you still using your original circuit, try the one I posted and set to 30% High period.

    E
     
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