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TDC1000: ToF is not changing

Gytis Kazlauskas1
Prodigy 30 points
Part Number: TDC1000

Hello TI Team,

I am working with TDC1000 where my goal is to measure ToF using Piezo ceramic transducer 1MHz. I am following snaa270.pdf application report (Using Ultrasonic Sensing to Monitor Level in Tanks) to test that my circuit and sensor is working properly, but no matter how far is my object from the transducer ToF is not changing. That it would be more clear that's what i did:

1) Configured registers for TDC1000 using SPI protocol. Register values can be seen below. (NOTE: I was not using TI GUI. Values was uploaded manually)

CONFIG_0

            RAW:                           0x44

            TX_FREQ_DIV:            8

            NUM_TX:                                4

CONFIG_1

            RAW:                           0x41

            NUM_AVG:                 1

            NUM_RX:                                1

CONFIG_2

            RAW:                           0x0

            VCOM_SEL:                 INT

            MEAS_MODE:             TOF

            DAMPING:                   OFF

            CH_SWP:                                 OFF

            EXT_CHSEL:                 OFF

            CH_SEL:                                   1

            TOF_MEAS_MODE:                0

CONFIG_3

            RAW:                           0xC

            TEMP_MODE:             REF, RTD1, RTD2

            TEMP_RTD_SEL:                     PT1000

            TEMP_CLK_DIV:                      8

            BLANKING:                  ON

            ECHO_QUAL_THLD:                -220 mV

CONFIG_4

            RAW:                           0x5F

            RECEIVE_MODE:                     MULTI ECHO

            TRIG_EDGE_POLARITY:           RISING

            TX_PH_SHIFT_POS:     31

TOF_1

            RAW:                           0x40

            PGA_GAIN:                  6 dB

            PGA_CTRL:                  ON

            LNA_CTRL:                  ON

            LNA_FB:                                  CAPACITIVE

            TIMING_REG[9:8]:      0

TOF_0

            RAW:                           0x1E

            TIMING_REG[9:0]:      30

ERROR_FLAGS

            RAW:                           0x0

            ERR_SIG_WEAK:                     0

            ERR_NO_SIG:              0

            ERR_SIG_HIGH:                       0

TIMEOUT

            RAW:                           0x23

            FORCE_SHORT_TOF:   OFF

            SHORT_TOF_BLANK_PERIOD: 128 x T0 -> 1600.00 us

            ECHO_TIMEOUT:                    ON

            TOF_TIMEOUT_CTRL: 1024 x T0 -> 12800.00 us

CLOCK_RATE

            RAW:                           0x1

            CLOCKIN_DIV:             1

            AUTOZERO_PERIOD:  128 x T0 -> 1600.00 us

TOF Control:                           Standard TOF

with blanking

2) Measured Start, Stop & Compin with osciliscope.

CH1 START CH2 COMPIN

CH1 START CH2 STOP

CH1 STOP CH2 COMPIN

3) Tried to move object closer to the transducer and further graphs stays the same.

4) Continued with snaa270.pdf and changed register values of TDC1000.

CONFIG_0

            RAW:                           0x44

            TX_FREQ_DIV:            8

            NUM_TX:                                4

CONFIG_1

            RAW:                           0x41

            NUM_AVG:                 1

            NUM_RX:                                1

CONFIG_2

            RAW:                           0x0

            VCOM_SEL:                 INT

            MEAS_MODE:             TOF

            DAMPING:                   OFF

            CH_SWP:                                 OFF

            EXT_CHSEL:                 OFF

            CH_SEL:                                   1

            TOF_MEAS_MODE:                0

CONFIG_3

            RAW:                           0xF

            TEMP_MODE:             REF, RTD1, RTD2

            TEMP_RTD_SEL:                     PT1000

            TEMP_CLK_DIV:                      8

            BLANKING:                  ON

            ECHO_QUAL_THLD:                -1500 mV

CONFIG_4

            RAW:                           0x5F

            RECEIVE_MODE:                     MULTI ECHO

            TRIG_EDGE_POLARITY:           RISING

            TX_PH_SHIFT_POS:     31

TOF_1

            RAW:                           0x40

            PGA_GAIN:                  6 dB

            PGA_CTRL:                  ON

            LNA_CTRL:                  ON

            LNA_FB:                                  CAPACITIVE

            TIMING_REG[9:8]:      0

TOF_0

            RAW:                           0x1E

            TIMING_REG[9:0]:      30

ERROR_FLAGS

            RAW:                           0x0

            ERR_SIG_WEAK:                     0

            ERR_NO_SIG:              0

            ERR_SIG_HIGH:                       0

TIMEOUT

            RAW:                           0x43

            FORCE_SHORT_TOF:   ON

            SHORT_TOF_BLANK_PERIOD: 8 x T0 -> 100.00 us

            ECHO_TIMEOUT:                    ON

            TOF_TIMEOUT_CTRL: 1024 x T0 -> 12800.00 us

CLOCK_RATE

            RAW:                           0x1

            CLOCKIN_DIV:             1

            AUTOZERO_PERIOD:  128 x T0 -> 1600.00 us

TOF Control:                           Short TOF

5) Measured Start and COMPIN

CH1 START CH1 COMPIN

This measurements i did just to test that my transducer and circuit is working properly before glueing transducer to the tank. So between object and transducer there is an air instead of water. I assume that ToF still should vary depending on the distance between transducer and object. Thank you.

Kind regards,

Gytis

  • 0
    TI__Genius 11015 points
    Gytis,

    Thanks for this details info, so the ToF varies while the transducer was tested in air and does not work when it was glued to a tank. Is the tank is made of plastic/metal? What is the drive voltage of the transducer in use? What is the minimum & max range of liquid level you plan to measure?
  • 0 in reply to Bharat Aravamudhan
    Prodigy 30 points

    Bharat,

    Thank you for your reply, i was not clear enough, so i will try to explain situation better. I only tested transducer in the air, because i didn't want to glue it to the tank before knowing that it is working properly. Everything is running on 3.3V except  LMH6601MG -  Operational Amplifier which has 5V. I am also adding a picture of my TX signal below. First of all i would like to test it in the air and see that my ToF is changing depending on the distance between object i want to measure and transducer. 

    1) Maybe my assumption is wrong that transducer should also work in the air without having obstacles(like tank wall) in between transducer and object i want to measure? (Is it only work when its glued? )

    2) What is the signal then which i see on my COMPIN ? (Is it noise?)

    Since i know that transducer and circuit is working my final goal is to measure liquid level inside the tank which is made from plastic. The maximum range of liquid level i am planning to measure is 15cm and the minimum 1cm. 

    I hope it is more clear. If you have more questions let me know. Thank you.

    CH1 TX CH2 COMPIN

  • 0 in reply to Gytis Kazlauskas1
    TI__Genius 11015 points
    Gytis,

    The transducer should be glued properly to the tank as shown in the application note in the link below:

    www.ti.com/.../snaa266a.pdf

    However I assume, you would like to check if the setup works before your actually glue to the system. In such cases, please place the transducer in front of a metal/plastic wall and then measure the ToF with the device. Please note while the medium is air in the GUI change the LNA feedback to resistive and check if you receive any signal from the reflection back. You may also need to increase the PGAGain.

    From the last screen shot you have provided me i can see a signal of about 1V in the COMPIN pin, but I cannot say for sure if it is real signal or noise.
  • 0 in reply to Bharat Aravamudhan
    Prodigy 30 points

    Bharat,

    I tried to change LNA_FB field to resistive and measure ToF, unfortunately it didn't work and i had the same results. I also tried to cover all the other sides of the sensor with hot glue and place sensor in front of my plastic wall that also didn't help. So i assume that in order to test the system and 1mhz disc the only solution is to glue it.

    I tried afterwards to glue disc to the tank and then it start working. (using snaa266.pdf)

    So there is no way that measurement of the liquid level could be taken without glueing your disc to the tank? (Maybe someone achieved this and share somewhere, but i am not aware of that)

    Thank you.

    Kind regards,

    Gytis

  • 0 in reply to Bharat Aravamudhan
    Prodigy 120 points
    I have the same equipment as Bharat and I would like to make water level measurements over a range of 1cm to 60cm.

    I use a 1Mhz transducer

    Can you suggest me a configuration for that?
    Thank you in advance.
  • 0 in reply to Gytis Kazlauskas1
    TI__Genius 11015 points
    Gytis,

    Glue'ing the transducer to the tank that is being used helps to remove any other medium in between and provides an accurate result.

    In case you want to measure a distance in air then using 1Mhz transducer will not help and you would need a transducer in the range say 40Khz to a 300Khz range.
  • 0 in reply to Bharat Aravamudhan
    Prodigy 120 points

    Thank,

    Is the 1Mhz transducer recommended for measuring the gas level?

  • 0 in reply to Christian Ngotchie
    TI__Genius 11015 points
    Chistian,

    If the medium is gas and not liquid we recommend that you use a lower frequency range (40Khz to 300Khz) transducer.