MSP430FR6043: High precision water meter

1) Based on our documentation, it seems that the ADC based correlation approach will result in a lower standard deviation in measurements. TI devices use an ADC based correlation approach.

2) The MSP430FR6047 is typically used for water metering. You can also use the MSP430FR6043 for water metering applications and more accurate time of flight data. However these parts also includes an LCD. If you have no need for an LCD, you could reduce costs by looking into the MSP430FR5043 or the MSP430FR5041. You can view all of our ultrasonic sensing parts to compare at this page. You can also see a list of which devices are capable of which types of measurement here.

3) One pipe and transducer set-up that we list on our own website is this one sold by Audiowell. I think many of our customers use Audiowell and Jiakang transducers. There are many other companies selling parts that will work with our device as well.

4) In our datasheet, we specify a delta-TOF accuracy of 25 ps for the MSP430FR6047 and 12.5 ps for the MSP430FR6043. I see in the TDC7200 datasheet they report that the conversion has an accuracy on the order of ps. These devices are hard to compare as the TDC appears to take in a start and stop pulse to determine time of flight, but includes none of the analog front end, or computational capabilities. If you'd like to assemble these parts on your own, you may find that this works better for you. The MSP parts I've referenced above include everything necessary to perform the measurements, aside from the transducers and the pipe. It sounds like the accuracy is comparable.

I'd like to note that the accuracy that you can achieve, with the MSP or other devices, is largely dependent on how well you calibrate it, and your hardware design. Reducing noise and making the best coupling between the transducers and pipe, as well as pipe material, and a multitude of other things, can all affect the accuracy of your measurements. While choosing the correct part to achieve an accurate measurement is critical, it is also very important to consider other hardware and environmental factors to achieve accurate measurements.

The second document that you've linked is a different application using a different microcontroller and analog front end set-up. The equation there is what they use in their implementation. In the MSP430FR504x and MSP430604x devices with the USS library, we use the first equation, mentioned in the first link.

My suggestion for finding the error rate would center around the final VFR. Of course, the final VFR is determined by the velocity, which is determined by the dToF, but basing your error on the final VFR means that you can connect your pipe to a mechanical flow meter, and easily view the actual flow rate vs the flow rate calculated by the MSP. Then you can fine tune the parameters as needed in order to match the reference meter as close as possible.

Alternatively, you could calculate the expected absolute ToF using the speed of sound in water, the distance between the transducers, and the velocity of flow (which you will have to collect using another reference meter of some sort). Then you can use this to compare to the absolute ToF the device finds, and you can calculate the delta-ToF by hand and compare it to the one the device finds as well.

As a secondary note: Since you are looking at using the meter across a range of different flow rates, you should take a look at the VFR Flow Calibration section of The Ultrasonic Sensing Design Center User's Guide, which allows you to calibrate for different ranges of flow rates with consideration for your error threshold.

thank you very much