Ultrasonic Flow Meters

Question 1

Explain the principle of operation of a Doppler ultrasonic flow meter.

Answer 1

The transmitter emits a sound pulse into the process medium and that pulse is reflected back to the transmitter by the particulate in the process.

Question 2

Explain the principle of operation of a Transit time ultrasonic flow meter.

Answer 2

The flowmeter measures the time for a sound pulse to travel against the flow and a pulse with the flow. The time difference is directly proportional to fluid velocity.

Question 3

What types of fluids can be measured with a time transit ultrasonic meter?

Answer 3

Clean, acoustically conductive liquid or gas flow

Question 4

What types of fluids can be measured with a Doppler ultrasonic meter?

Answer 4

Entrained particles need to be present, acoustically conductive liquid

Question 5

What are the advantages of ultrasonic flow meters?

Answer 5

1) Non intrusive
2) No pressure loss
3) Bi-directional
4) Linear output
5) Not affected by process density, temperature, or pressure

Question 6

What are the disadvantages of ultrasonic flow meters?

Answer 6

1) (Transit time): Process fluid must be clean
2) Alignment is critical
3) (Doppler): flow has to be fast enough so that particles don’t settle
4) (Doppler): Flow must have solids

Question 7

In a frequency difference ultrasonic meter how is the rate of transmitted sonic pulses controlled?

Answer 7

Transducer A sends a signal to transducer B. Once transducer B receives that signal it initiates transducer A to send another signal and vice versa.

Question 8

What are the two mounting considerations when installing ultrasonic flow meters.

Answer 8

1) Ensure that the transducers are aligned
2) Make sure that the pipe has no entrained air, pipe has to be full