TDC1000-C2000EVM: Mode 2 operation, remove R80 and R81 ?

Simon,

Removing R80 and R81 is not necessary in Mode2 given this mode's channel definitons are the same for Mode1 (Channel 1 = "TX1/RX1" and Channel 2 = "TX2/RX2"). Currently, the TDC1000-C2000EVM's R80 shorts TX2-RX1 and TX1-RX2. This means if you are transmitting on TransducerA connected to TX1 of R81, the opposing RX1 receiver (TransducerB) is still isolated on the other short of R80. In fact, my understanding of this mode indicates you must keep R80 and R81 populated to properly utilize Mode2's channel swapping benefit.

I recommend that you view the sections pertaining to flow metering on the TDC FAQ page here:

https://e2e.ti.com/support/sensors/f/1023/t/724028?TDC1000-Everything-You-Need-to-Know-for-Ultrasonic-ToF-Liquid-Coupled-Collateral-Tools-Designs-FAQ-

These additional articles and resources should help you with the device configuration to enable flow metering.

Note: The TDC1000 is no longer recommended for flow applications, only level sensing or static concentration/identification applications. The TDC1000 flow meter configuration is known to have issues in repeatability and accuracy when there is no flow (with or without water present). The TDC1000 is no longer recommended for flow applications, only level sensing or static concentration/identification applications. You can continue to use the TDC1000+TDC72000/+C2000 combination for water flow measurement, but you are taking a risk a inconsistent accuracy due to a device bug whereby the first stop pulse is occasionally missed (does not toggle STOP pin on TDC1000). Considering flow metering relies heavily on nano to pico-second timing accuracy, missing the stop pulse can have a significant impact on the flow rate measurement. As a workaround, it is possible to perform multi-cycle averaging to compensate for the occasionally missed first stop pulse. 

Due to the potential issues of the TDC1000, we recommend the specialized MSP430 devices for flow metering applications: 

• http://www.ti.com/microcontrollers/msp430-ultra-low-power-mcus/ultrasonic-performance-sensing-mcus-overview.html
• http://www.ti.com/tool/MSP-ULTRASONIC-DESIGN-CENTER

We are also exploring the use of the new TUSS4470 and TUSS4440 devices for ultrasonic flow metering.

Hi Simon,

I do not support the MSP430FR6047 device directly, so I recommend you start a new E2E thread pointing to this device or the TIDA-01486. However, I will still try to answer your questions:

1) My understanding is that the MSP430 ultrasonic devices are limited to driving transducers directly with a 3.3V square wave. If you need to excite the transducer with a larger driver voltage, you will need to use the MSP430's driver signal as a pre-driver to an external boosted driver circuit (as in the TIDA-01486), or use a different device. The PGA460, TUSS4440, and TUSS4470 devices can excite transducers directly upwards of >+100V, >+100V, and 36V respectively. These are devices I support, but as mentioned in my last response, we are still exploring their feasibility in flow metering.

2) Many TI-Designs are only available as paper reference designs. This solution may not be orderable, but you can confirm with the MSP430 team.

3) The sample rate is dependent on your required flow rate step resolution. I suspect an 8 MSPS is feasible for flow metering purpose. To give some perspective, the PGA460 has an integrated 1 MSPS ADC. Assuming you were monitoring the flow rate of air (i.e. anemometer), the PGA460's flow rate step resolution is limited to an absolute minimum of ~343um (from 343m/s ÷ 1MSPS, or speed_of_sound ÷ sample_rate). If 1 MSPS if sufficient for your needs, then the PGA460 could be used. Otherwise, the MSP430 with its 8 MSPS ADC, or the TUSS44x0 with an external ADC of your choice.