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TIDA-01486: Extreme Noise/Oscillation When combining EVM430-FR6047 with TIDA-01486

Part Number: TIDA-01486
Other Parts Discussed in Thread: EVM430-FR6047

Hello, 

For a clamp-on flowmeter design we use the EVM430-FR6047 together with a self designed sensor with a piezo-disc. We already tested the EVM430-FR6047 stand-alone with these sensors and got good results with a steel pipe of nominal diameter of 80mm. In this setup we needed to set the PGA to max  amplification (30.8dB) and the ADC values reached max  a value of ~1000. But for some applications with bigger pipe diameter or special pipe material (stainless steal) we need higher driving voltage to increase the SNR or even measure any response.

We connected the EVM and the TIDA as described here: https://e2e.ti.com/support/microcontrollers/msp430/f/msp-low-power-microcontroller-forum/835040/ccs-evm430-fr6047-tida-01486-mistakes 
So we removed R16/R17 and C11/C12 on the EVM board and splitted CHx_in and CHx_out. I attached a picture that shows the connection.

 

We removed on the EVM side the capacitors and resistor at the connector for the transducers. These are added again but in the wired connection (Troubleshooting).

 

I will try to describe what I experience:

  • I connect the transducers to the TIDA board and connect the EVM connector from the TIDA to the EVM board.
  • The voltage supply for the TIDA board is connected and switched on (+-12V)
  • I connect the EVM board to my computer via USB
  • In the USS software I connect to the EVM board
    • The ADC capture shows no signal and the error Message comes up: No signal detected in up and downstream channel
    • In parallel I measure the driving and receiving signal of the piezos: The signals looks good right now! (see attached picture 20210216_103422.jpg)
  • I set the Param #10 in the USS software to 1 and push “request update” button à update is successfull
    • The ADC capture shows some not interpretable signal (see attached picture 20210216_103512.jpg) and error message: DToF - Shift value was greater than maxSampleShift
    • The measured signal with the oscilloscope changes extremely: Driving signal is still good, received signal is extreme “noisy” and changes over time (picture attached 20210216_103529.jpg & 20210216_103832.jpg: green driving, yellow receiving)
    • Also attached is a csv file of the ADC capture

  • Hello Maik,

    Could I please see how you connected the wires on the EVM side?

    From the ADC capture image it seems you have an offset in your receiving signal. The receiving signal should be centered around zero. 

    Where are you probing the received signal on the board? it seems that your received signal is at around 100us but you are capturing a lot of noise before that. Noise could couple to your received signal from everywhere. I would suggest to start to twist each signal with his own ground and separate as much as you can transmitting with receiving wires and finally also the two channels wires. 

    Hope this helps.

    Best regards

    Giovanni

  • Hi Giovanni,
    Thanks for your answer. Find attached a picture of the EVM board connection.

    The probing of the signal is directly at the transducer connector of the TIDA board.
    We already did seperating the signals and measured each path alone. 
    The noise you see only comes up when both transducers are connected.

  • Hello Maik,

    It seems from the picture that you have removed R16, R17, C11 and C12 from the EVM. The measurements done by TI have these 4 components still soldered on the board. See picture attached.

    Could you please re-solder them and run the measurements again.

    Thanks

    Giovanni