TDC1000-Q1: Receiving signal Problem

Hello,

The speed of sound through air is about 20% of the speed of sound through water. Because of this, attenuation of sound through air is much greater than through water. The signal is too weak to be received after traveling through air. The TDC1000 is not designed to provide an output strong enough to drive most transducers intended for air-coupled applications. If it is necessary, please see the TDC1000-GASEVM which includes a voltage boosting daughtercard designed for use in gas flow meters.

Hello Scott,
i have gone through that point you specified so that i have tried BSTEVM circuit that is shown in TDC100-GASEVM document but after this circuit completion now am able to receive echo when the transducers are placed inside the water, Since am doing non-intrusive type of flow meter if i place the transducer outside the pipe am not able to receive the echo.
the transducer am using is from audio-well that has specified in one of the TI's documentation.
What would be the problem please guide me.

Regards,
Rashmi H M

Hi Rashmi,

I would guess most of the energy from transducer is reflected by the water pipe. Depends on the thickness of the pipe, you probably won't be able to see any receiving signal.

But I think two approaches might be helpful for you. First, increase you transmitting signal strength by driving it to a much higher voltage level. Transducers that can handle up to 200Vpp or even higher is not hard to find. Second, try implement a filter between LNAOUT and PGAIN. A passive filter may not be enough. You may need a higher order, bandpass or low pass filter.

Second method seems to be less pain. I would recommend start from there.
Hopefully this gives you some idea to start with.

Thanks!
JY

Hello JY,

               Thanks for the reply,I have tried first method as you specified i have increased the transducer peak to peak voltage but it is not much helpful.So,i want to try second method can you please suggest me how to implement the filter between LNAOUT and PGAIN  because i have designed the filter between PGAOUT, COMPIN and VCOM. please suggest me how to implement a filter.

Advance Thanks,

Rashmi HM 

Hello Rashmi, 

How high the driving voltage you went up to? Also, is the transducer attached to the pipe closely? 

I am also working on a prototype build now. So, for receiving end, I am planning to use a filter that TI app notes suggested. It is centered at 200KHz. Depends on your transducer, you may need to adjust the filter's center frequency. However, I only read through this app notes, but I haven't built it myself yet. I attached the link below:

 

Let me know how it goes!

Thanks!

Liang

Hello Liang,

                    I am able to achieve about 30v peak to peak(Driving voltage).Know am also able to receive the echo signal and i have attached the transducer as close as possible to the pipe.

i)you have mentioned that ,so for receiving is end then why you need to design the filter ....?

ii)I am using 1Mhz transducer for my application

Hi Rashmi,

You made me little bit confuse. So you mean you were able to see the echo signal after you use 30Vpp driving signal?
Receiving filter has beneficial that can amplify the receiving signal as well as filter out other noise.

Do I answer your question?

Thanks!
Liang

Hi Liang,
Yes am able to receive the echo signal after am using 30Vpp driving signal but in the receiver part i have directly connected receiver pin to VCOM pin
i)If i connect RX transducer to RX pin of TDC100 i am not able to receive echo signal so,i want to use filter between LNAOUT and PGAIN please suggest me how to build filter so that am able to amplify received echo signal..?

Regards,
Rashmi hm

Hi Rashmi, 

If that is the case, which means you are able to receive echo signal, then you can use the internal low noise amplifier and programmable gain amplifier inside TDC1000. Those should get you enough gain.

Give that a try!

Thanks!

Liang

Hello,

         Sorry for the late reply,i have used internal low noise amplifier and and i have used  PGA GAIN how much i can use but am unable to receive proper echo signal when i place transducer at RX pin of TDC1000.

Regards,

Rashmi HM

Hi Rashmi, 

If that is the case, since you mentioned you previously was able to see the echo, then my first guess is your receiving signal is not strong enough. Please refer to the application note that I sent to you previously and build that 3 stage filter. You may start with simulate them, either LMV881 or LMV861 should work for you. TI website gives you a macro model for both op amp, I think it is good place to start with. 

Thanks! Hope that answers your question.

Liang

Hello Liang,
thanks for the pdf i tried and now am able to receive the echo signal.
i)now am moving forward to calculate TOF so am using TDC7200 am trying to read and write the registers of TDC7200 but am unable to write CONFIG1 register of the TDC7200 ...?
Please help me out regarding how to read and write TDC7200...?

Regards,
Rashmi H M

You should install the TDC1000-TDC7200 evaluation software. After you done that, you should be able to see the source code. In the source code, you can find many already written and tested source code, which includes SPI read/write function. Give that a try, it should be very straight forward.

Thanks!

Liang

Hi Liang,

Thank you for your support.

Rashmi,

I believe that Liang has answered your question. I will go ahead and close this thread for now, but if you need additional assistance with this issue please reply again and it will automatically reopen.

Thanks,

Hello Scott,
I tried to install evaluation software but am unable to install the software and still i dint get source code so please don't close this thread

Regards,
Rashmi HM

Hi Rashmi,

I have attached the TDC1000-TDC7200EVM firmware source code. Other example projects are included for SPI transactions with the MSP430.

TDC1000_7200EVM_Firmware_Source-v2.01.zip