OPAX607 datasheet(28/49 Pages) TI

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9.6 Clamp-On Ultrasonic Flow Meter

Figure 9-6 shows how ultrasonic flow meters measure the rate of flow of a liquid using transit-time difference

(t12–t21), which depends on the flow rate. Figure 9-6 shows a representative schematic for a non-intrusive

ultrasonic flow meter using the OPAx863 devices and 12-V transducer excitation. The OPAx863 devices are

used for the forward path as a unity-gain buffer for 12-V pulsed transducer excitation at Node 1. At the same

time, the receiver circuit at Node 2 (which also uses the OPAx863 devices) first provides an AC-gain followed by

a DC-level shift to lead to the PGA, ADC, and processor within the MSP430 microcontroller.

Node 2 and Node 1 use similar transmit and receive circuits (discussed previously) for the reverse path. The

OPAx863 devices wide GBW of 50 MHz introduces minimal phase-delay and low-noise for superior flow rate

measurement. The amplifier stays in power-down mode for a majority of the time in battery powered systems,

resulting in very small average system-level power consumption and prolonged battery lifetime with its 1.5 µA

(maximum) power-down mode quiescent current with a 3-V supply. Since the transmit and receive signal chains

are connected to the same point at the respective node transducers, the OPAx863's 12.6-V supply voltage

capability enables 12-V transducer excitation without any damage to the front-end or need for external switches

which makes a compact solution. This makes the OPAx863 devices suitable for flow measurements in large

diameter pipes and non-intrusive flow meters. The TIDM-02003 reference design discusses an ultrasonic gas

flow sensing subsystem which uses high-speed amplifiers for front-end amplification.

OP Ax863

12 V

ISO

Filt

AC2

R¶

3.3 V

PGA

ADC

MSP430FR6043

OP Ax863

Processor

Transmitter

Receiver

Transmitter

NODE-1

NODE-2

3.3 V

12 V

0 V

12 V

0 V

12 V

R X

AC1

12 V

Figure 9-6. Non-Intrusive Ultrasonic Flow Meter

OPA863, OPA2863, OPA4863

SBOS982H – JUNE 2020 – REVISED AUGUST 2022

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