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TDC1011: Maximum range detection for water level monitoring

Rakesh Kumar2
Prodigy 40 points
Part Number: TDC1011
Other Parts Discussed in Thread: TUSS4470, TDC1000, TDC1000-C2000EVM

Hi ,

We are planning to use TDC1011 AFE for water level detection for  0.2meter to 4meter.

What is that limits the maximum range:

1. Is it TX power?

2. Is there range limit on TDC1011?

3. To measure 4meter range total distance travelled will be 8meter, will there be enough received power after 8meter of travel ?

In datasheet its i mentioned: "Measurement Range: Up to 8 ms"  Does it mean maximum TOF is 8 milli Seconds?

regards,

Rakesh

  • 0
    TI__Expert 3450 points

    Hi Rakesh,

    There are many factors that can impact the range and quality of the received ultrasonic echo, for example:

    transducer frequency, ToF medium material, transducer mounting, TX voltage, transducer excitation length (number of TX pulses), AFE receiver gain, target shape and material, transducer field of view (beam width), and overall quality of the transducer. 

    The TDC1011 also has an 8ms (yes milliseconds) ToF limit, which is roughly 12m round trip distance in water and 2.7m round trip distance in air. 

    So this could work if the transducer is transmitting through water. To maximize the distance, you may have to experiment with the transducer frequency, mounting, number of TX pulses, and LNA gain. 

    However, for the 0.2 - 4m range, air coupled or water coupled, I would recommend the TUSS4470 AFE. It can drive 10x the TX voltage (36V) of the TDC1011, and has a logarithmic gain amplifier in addition to a LNA that produces a higher SNR for longer range applications. The TUSS4470 supports up to 1MHz transducer, for water or air coupled ToF applications. 

    Here are some further resources:

    Ultrasonic Sensing Basics for Liquid Level Sensing, Flow Sensing, and Fluid Identification Applications

    Using Ultrasonic Sensing to Monitor Level in Tanks (some TDC1000 range data)

    Logarithmic Amplifier for Ultrasonic Sensor Signal Conditioning

    TI Precision Labs Ultrasonics

    Regards,

    Gabriel

  • 0 in reply to Gabriel Lake1
    Prodigy 40 points

    Hi Gabriel,

    Thanks for response.

    Why there is limit of 8ms? Can this be changed if I feed lower frequency clock to chip ( for example 2MHz instead of 8MHz) or using any register settings?

    I am planning to use ultrasonic sensor using battery powered (3V) & TDC1011 AFE is ideal for that but TOF limit if 8ms is bottleneck.

    regards,

    Rakesh

  • 0 in reply to Rakesh Kumar2
    TI__Expert 3450 points

    Hello Rakesh,

    The record length limit is not a function of the clock frequency, unfortunately this cannot be increased above 8ms. See post 3018946 for more information. 

    It sounds like you plan to measure through the water. If that is the case, the 8ms record length limit should be enough time. 

    Regards,

    Gabriel

  • 0 in reply to Gabriel Lake1
    Prodigy 40 points

    Hi Gabriel,

    Thanks for the response.

    Could I disable the TIMEOUT & extend the RX mode till I get stop pulse  or desired timeout in MCU.

    Please check the datasheet section 8.4.6.5.

    Also please help me understand how 8ms of timeout is calculated.

    If I give clock in with frequency of 100KHz & setting the CLOCKIN_DIV=1  means divide by 2. Hence T0= 2/Fin= 0.02ms

    Setting TOF_TIMEOUT_CTRL=3

    Maximum Echo listen timeout is 1024*T0 = 1024 *0.02ms = 20.48 ms 

    I am planning to use 40KHz transducer.

    I have also shown the usage setup of a tank with maximum depth of 4 meters.

    Most of the travel media will be air when tank is almost empty.

    regards,

    Rakesh 

    1. Setup diagram.

    2. TI datasheet, mentioning disable of Timeout.

  • 0 in reply to Rakesh Kumar2
    TI__Expert 3450 points

    Rakesh, 

    Please see this response on the TOF_TIMEOUT_CTRL. 

    T0 in the datasheet is the clock period after being divided. The default for 40kHz would be 6.4ms

    The maximum timeout is still 8ms, but as you pointed out, the echo timeout can be disabled and the datasheet recommends limiting the record length to 100ms. I have not tested this feature, and cannot find previous reports of customers posting about this, but this looks like a viable option for you. If the STOP is not received, you will have to interrupt the measurement manually. 

    Regards,

    Gabriel

  • 0 in reply to Gabriel Lake1
    Prodigy 40 points

    Hi Gabriel,

    Thanks for the response.

    Is there possibility to check the timeout feature disabled by TI app team & report the maximum range in Air?

    regards,

    Rakesh

  • 0 in reply to Rakesh Kumar2
    TI__Expert 3450 points

    Rakesh,

    The 8 ms value in the datasheet is calculated using the two formulas listed in green in the diagram under section 8.4.6.2, with T0 = 1us, which is the default value when using the TDC1000-C2000EVM. We realize this is misleading, as the formulas would not be able to account for lower frequency transducer excitation if 8 ms is a hard cut-off value. 

    I have started testing this feature, and I will let you when I'm ready to share the results. While the results may not reflect the actual maximum range (distance), this information should be useful and clarify the datasheet contradiction. 

    Regards,

    Gabriel

  • 0 in reply to Gabriel Lake1
    TI__Expert 3450 points

    Hello Rakesh,

    I made a miscalculation in one of my previous explanations, I'll clarify here: 

    with clock in = 100kHz, and CLOCKIN_DIV = 1 (divide by 2), T0 = 2/100kHz = 0.02ms. The maximum timeout  for the standard measurement mode, according to the formula in section 8.4.6.2 is

     

    with TIMING_REG and TOF_TIMEOUT_CTRL at their maximum values of 1023 and 1024*T0 respectively, the calculated time would be:

    ((1023-30) * 8 * 0.02ms) + 2^(1024*0.02ms) * 128 * 0.02ms = 0.15888 + 0.0025966 seconds ~= 161ms. 

    The 8ms value is listed as the maximum timeout duration in the datasheet because although the device is able to support lower frequency transducers, it is not well suited for air-coupled applications with transducers below 1MHz, where the ToF approaches 8ms. 8ms would have been calculated from a 2MHz input clock with CLOCKIN_DIV set to divide by 2, T0 = 1us.

    In an air coupled test with a 220kHz transducer, it was found that the TDC1000 does not have sufficient gain to detect the return echo over an 8ms ToF. We are not able to perform an 8ms+ ToF test in water due to the size of the tank required. 

    My recommendation for using the TDC1000 in ToF measurements exceeding 8ms is to disable the timeout and end the measurement manually with a RESET or writing 0x03 to register 0x7, but to justify this, you would need evidence that the return echo can be received at such a distance. 

    The TUSS4470 would be a much more feasible and robust device to fulfill your application requirements. 

    Logarithmic Amplifier for Ultrasonic Sensor Signal Conditioning

    40kHz transducer:

    Regards,

    Gabriel