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TDC1000: Concentration mesurement setup with changing temperature - echo pulse top/bottom dynamic change

cagabit
Prodigy 20 points
Part Number: TDC1000
Other Parts Discussed in Thread: TDC1011

Hi,

Trying to develop a sensor system with TDC1000 / TDC1011 for concentration reading of a specific liquid in a temperature range 10-40C. Build a measurement chamber from plastic , using x1 transducer of 1Mhz, and a microcontroller to read TOF values from the TDC. At constant room temperature everthing seems to be ok, there is strong echo returning and the START-STOP signals are also readible.  Tried almost all settings of the TDC and also putting the sensor to outside of the wall of the chamber OR drilling a hole and putting the sensor surface directly relation with the liquid.

The problem is ; when you change the temperature high or low, the shape of the echo changes slightly, like amplitude of the first pulse changes or the order of positive and negative pulses change. And this affects the treshold trigger of the system which in relation affects the tof results. As an example lets say you have 5 pulse echo ( 5 up and down cycles ) , at 20C because of the amplitude of the first pulse the STOP is triggered with the first pulse but at 40C the amplitude of the first pulse decreases ( but still strong enough) and as it is under the level of treshold, the next pulse which has a bigger amplitude causes the trigger, in the end the result changes at least 1 pulse width.

Tried to average various number of readings, or some error catching algorithms but withoud any good results, since the change of the trigger is huge!

Do you experience such a thing, can you think of any solution or idea about the problem ? 

  • 0
    TI__Genius 11015 points
    Cagan,

    Please send me the plots of the Rx signal, STOP START signals.
    Try to increase the threshold of the VCOM & the PGAIN and check if you still see a discrepancy.
    Try to change the receive mode from single echo to multi echo.
  • 0 in reply to Bharat Aravamudhan
    Prodigy 20 points

    Hi Bharat,

    Thanks for the reply.

    Here is the example senario:   These were saved under these settings;

    #Tx=1, #Rx=0, Thershold=3, PGA=bypass (no gain), Short=1, AutoZero=0

    This is saved at 23C, with water:

    This is the same, zoomed:

    This is taken at 28C, with water, with the wave form slightly changed:

    As you can see with the change of the first pulse of the echo, the number of STOP pulses changes.

    This is just an example of many senarios I tried. Enabling PGA, setting different gain values with different trehold values, also with different measurement chambers.

    Also tried the "multi echo", since I am after the price TOF, even with the multi echo setting, when the first pulse cahanges, the start of the STOP pulse changes, which makes a huge difference on the result.

    When you test these settings with water and a diluted solution of a subtance ( for concentration measurement ) , first the settings you choose seems to be working well up to a temp point, then not, or if working well for water for all the temp span, it is not working for the other concentration of the substance. Is it too wide to test both with temp and concentraion ?

  • 0 in reply to cagabit
    TI__Genius 11015 points
    Cagabit,

    I understand that you are using this part for concentration measurement. Please characterize the part for optimal condition for extreme condition of the concentrations. The number of STOPs should depend on the expected number of STOP you setup the device. There will be slight variations in the ToF during changes in temperature since the speed of sound changes in liquid.