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Sensors for TDC1000

Hithesh
Genius 3290 points
Other Parts Discussed in Thread: TDC1000

What kind of ultra sonic sensors can be used with the TDC1000.

Can we use the hobby grade ones - http://www.parallax.com/product/28015

or will be work only with the piezo type as mentioned in other thread - http://www.steminc.com/PZT/en/piezo-disc-transducer-450-khz

Does the Eval board include any sensors?

  • 0
    TI__Intellectual 1635 points

    Hi Hitesh,

    I am assuming you are working on distance application (not fluid level or flow).  If that is the case, there are the two sensors we have been using: ProWave's  400PT160 or Murata's  MA40H1S-R.

    What kind of resonant frequency is the one from parallax.com? I wasn't able to find it in its spec.  For air application, the typical resonant frequency transducer we've been using is in the 40kHz range.  Because of this reason, Steminc's transducer has a 450kHz might not be ideal for your air application.

    The eval board does not come with sensors.

     

  • 0 in reply to AmyLe
    Genius 3290 points

    Amy, I am working on water level sensor. 

    I think the parallax sensor resonant frequency is around 40KHz.

    Why does the functional diagram in the TDC1000 page show once sensor in bottom and other on the side. Is it just a representation.

  • 0 in reply to Hithesh
    TI__Intellectual 1635 points

    Hi Hitesh,

    For water application, we recommend a transducer with frequency in the 1MHz range.  One example is Steminc's  SMD10T2R111.

    The TDC1000 shows a sensor connected on the bottom to measure fluid level, and the second sensor is connected on the side is used to measure the concentration of the fluid inside the tank.

  • 0 in reply to AmyLe
    Prodigy 105 points
    Hi Amy,

    but is it possible to put the transducer on the top side of the tank, calculate the air level from the sensor (on the cap of the tank) to the surface of the liquid and then calculate the real level of the liquid; height of the tank - air level?
    In this case I have to consider the transducer in air at 1Mhz range even if I want to calculate liquid level, I am right?

    Thank you in andvance.
    Daniele
  • 0 in reply to Daniele Simioni
    Prodigy 105 points
    I meant transducer in air at 40kHz (not 1Mhz)
  • 0 in reply to Daniele Simioni
    TI__Expert 3835 points

    Hi Daniele,

    Right, the typical transducer range for air applications is 40kHz. What is the material and thickness of the bottom of your tank?

    Thanks,
    Sergio

  • 0 in reply to Sergio
    Prodigy 105 points

    Sergio,

    Imagine a plastic tank, 15-20 cm height.

    When it is empty there will be 0cm of liquid and 20 cm air, when the tank is full there will be 15cm of liquid and 5 cm of air.

    I want to put the transducer on the top side of the tank (in the cap) and then measure the level of the air to know indirectly the liquid level.

    It's possible? In this case I have to use air transducer at 40kHz I suppose.

    Can  I use ultrasonic for this short range?

    Thank you.

  • 0 in reply to Daniele Simioni
    TI__Expert 3835 points
    Hi Daniele,

    Is there any concern with the air transducer being inside the tank?

    It may be easier from the bottom and through the liquid. For a plastic container (PVT, acrylic or similar) you could place a 1MHz-range transducer on the bottom of the tank on the outside and measure the level directly.

    Sergio
  • 0 in reply to Sergio
    Prodigy 105 points

    Yes, I know that it is easier to measure directly the level from the bottom; but I can't.

    My constrain is to put the transducer on the cap.

    It' s possible to measure the liquid level as I described in the previous post?

    Thanks

    Daniele

  • 0 in reply to Daniele Simioni
    Prodigy 105 points

    Sergio, Amy,

    Could you help me to understand if, what I've described in the previous post, is a possible way to measure liquid level?
    I need your answers asap because in these days we are going to decide if this kind of sensor is ok or not for our purpose.

    Thank you in advance

    Daniele

  • 0 in reply to Daniele Simioni
    TI__Expert 3835 points

    Hi Daniele,

    What you propose is possible, but your end-goal should determine if the method is suitable for you.

    Measuring through air would be less precise than through the liquid. Pulse skipping with a 40 kHz transducer in air could translate to approximately a 25 us shift, while pulse skipping with a 1 MHz transducer in water could result in approximately 1 us shift. These equate to approximately 0.9 cm and 0.2 cm respectively. Averaging of multiple cycles would help in both cases.

    I tried a rough setup with the TDC1000 driving a 40 kHz transducer. The external components need to be adjusted to operate in this frequency range. Due to the long ring-down of the transducer, I was forced to use a dedicated TX transducer and a dedicated RX transducer.

    So, these are two things for you to consider.

    Regards,

    Sergio

    PS. Here are some rough distance measurements:

    distance_5cm.tif

    distance_10cm.tif

    distance_20cm.tif

  • 0 in reply to Sergio
    Prodigy 105 points

    Many thanks Sergio for your answer and your considerations.


    I am not an expert about ultrasonic sensing so I ask to you to give more details about the setup that you tried.
    Which external components did you configure? How to adjust?

    Thank you,

    Regards.

    Daniele

  • 0 in reply to Daniele Simioni
    TI__Expert 3835 points
    Hi Daniele,

    I configured the LNA in the front-end in resistive mode, as shown in Figure 17 of the datasheet, and the external components that need adjustment are those shown in Figure 19. The filters in Figure 19 are configured for frequencies of a few MHz, so the frequencies of these filters should be adjusted.

    In Figure 19:
    * The capacitor CF1 makes a high-pass filter with the input resistor of the PGA (500 ohm).
    * The resistor RF1 and the capacitor CF3 make a low-pass filter.
    * The capacitor CF2 and the resistor RF2 make another high-pass filter.

    These filters should be modified to allow your 40 kHz through.

    Regards,
    Sergio
  • 0 in reply to Daniele Simioni
    TI__Expert 4725 points

    Daniele,

    Sensing from the top of the tank has several issues that sensing from the bottom resolve. Specifcially

    1. what ranges do you need for measurement? ranges shorter than the ringdown time of the transducer require a second transducer and a "pitch catch" topology.

    2. Condensation droplets defocus the utlrasound beam.

    3. transducer cost inceases signifacantly as it needs to impervious to the fluids in the tank.

    regards,

    If this answers your question please click "verified" below 

  • 0 in reply to Sergio
    Prodigy 60 points

    Hi Sergio,

    as you did work with 40 kHz transducerd could you kindly tell the values of CF1,RF1,Cf3, CF2 and RF2 you worked with?

    Regards

    Reiner

  • 0 in reply to Reiner Mende
    TI__Expert 3835 points
    Hello Reiner,

    I briefly set up a quick experiment using the following components:
    RIN = 900 ohm (LNA in resistive feedback mode)
    CF1 = 10nF
    CF2=CF3=2.2nF
    RF1 = 1 kohm (no change)
    RF2 = 5.1 kohm (no change)

    I did run into the problem that Matt just mentioned, about having to use a second transducer to be able to catch the return echo. The distances I was looking at were approximately between 5-20cm.

    Regards,
    Sergio