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TDC7200: Application

Naser S.
Genius 11605 points
Part Number: TDC7200
Other Parts Discussed in Thread: TDC1000

Customer is interested in TDC7200/TDC1000 for two projects.

(1) To measure Helium purity "within 0.1%". We're told we have to measure sound velocities around 1000m/s and velocity change of 2.8m/s. The whole thing is highly temperature dependent.

The customer wants to "minimise" the physical path length.

Are the above products capable of the desired resolution?

(2)
To measure sewer water flow rate; the sensors will have to be entirely inside a fairly large, half-full and pretty turbid mains sewer. Flow velocities are (I think) pretty low, say 0.5m/s up to 5m/s..

 

  • 0
    TI__Mastermind 31655 points
    Hi Naser,

    1. The speed of sound through the helium will be equal to 2*Distance of measurement / time of flight. The resolution for the time of flight will be limited by the frequency of the transducer used and by the distance across which the time of flight is measured.

    For example say the speed of sound in a control experiment was found to be 1000m/s. You would expect a time of flight of 200us at a 10cm distance. If you were using a 1Mhz transducer, the TOF resolution would be 1us.

    Changing the TOF from 200us to 201us would result in a new measurement of 995m/s, a 5m/s difference or 0.5% resolution.

    If the resolution of the transducer is fixed, changing the distance will increase the resolution proportionally. For example, if instead the distance were over 20cm, then a 1us deviation would equate to a 0.25% change in the calculated speed of sound.

    The short answer is that the resolution will depend more on the transducer frequency and distance of measurement than the TDC1000 or TDC7200's circuitry. The TDC7200's time resolution is 55ps, which is much greater than the limitations of the transducer frequencies. So in order to achieve the resolution they are interested in they will have to carefully choose the transducer frequency and distance over which they are measuring. The TDC1000 and TDC7200 should be a good fit for this application.

    2. The TDC1000/TDC7200 combo are designed with fluid flow measurement in mind, and they would also be a good fit for this application, depending on the accuracy requirements. However, turbulent flow with lots of air incorporated can be difficult to measure accurately for even the best system.

    Regards,