MSP430FR6047: Impedance matching and ZFD accuracy

Hi,

I'm not sure how the values of the RC was determined. I will have to get back to you on that. 

What is the lowest flow rate you are trying to measure?

Regards,

Evan

It is 5 lph.

Regards,

Piyush

The RC values were selected to work with a number of commonly available transducers. I don't know the calculations used to find their values.

I still working on getting an answer about ZFD expectations.

Regards,

Evan

Hi Evan,

Can you please check on the RC calculation also?  It will be very helpful for us.

Regards

Piyush

Hi,

Please refer to 

https://www.ti.com/lit/ug/tidudn0/tidudn0.pdf for details regarding ZFD. 

Regards,

Evan

Hi Evan,

I have checked the same document but its not clear the doubt/querry.

In practical applications, it is not good to spend 100 or 200 seconds for averaging the DtoF. Although we are taking the samples on 8Hz but samples are distributed between +- 100ps. Can't we reduce this margin with impedance matching.

TI's other document telling about the impedance matching SLAA837A.

"Good impedance matching reduces dTOF drift at zero flow. How can transducers be well matched? What parameters are most important? How can the matching be adjusted?"

Regards,

Piyush

Hi Piyush,

Who is the manufacturer of the transducers and what are the specifications/tolerances?

Hi Dennis,

Transducer specifications are as per below,

• The sensitivity：-21.6dB
• Peak frequency：1.048MHz
• Center frequency：1MHz
• The static capacitance：800pF~1600pF
• Harmonic impedance：＜25Ω
• Waterproof level：IP68
• Working temperature：5℃~100℃
• Temperature drift：＜20KHz
• Ultrasonic time delay：5uS
• Qm Value：0~4.5
• Transmitted beam Angle：5°~10°

Regards

Piyush

Hi Piyush,

I'm not able to find specific instructions for matching the transducers so I have reached out to one of our experts in Shanghai.

Hi Dennis,

Any progress on this.

Regards

Piyush

Sorry, no progress to report.

Here's what I was able to find:

You can compare the peak frequency, capacitance and the impedance between the transducers for better matching. The capacitance and the impedance are more important.

Hi Evan,

Are you talking about the comparison between both transducer? 

Regards

Piyush

Ultrasonic Flow Transmitter Reference Design is the best resource I've found for impedance matching. See section 2.2.4:

I hope that help, I don't have more information that this.

Evan