# Flow Meter Interview Questions & Answers Part-1

In this article, we will see some of the important questions and answers related to flow meters asked in interviews, tests, and viva.

### Question 1: What are the three main types of flow meters?

Three main types of flow meters are as follows.

• Inferential flow meter
• Mass flow meter
• Volumetric flow meter

### Question 2: What are the factors that affect the flow rate?

• The factors affecting the flow rate are the density of the moving fluid, the viscosity of the moving fluid, temperature and the state of the moving fluid, pipe size, and the friction between the fluid and the pipe surface.

### Question 3: What is an Inferential flow meter?

• Inferential flow meters measure the flow by inferring the flow through any given pipe through some other physical property of the flow stream, which can be a Differential Pressure, variable area flow meter, Magnetic flow meters, Turbine flow meters, Target flow meters, Thermal flow meters, Vortex flow meters, and Ultrasonic flow meters.

### Question 4: What is the differential pressure generating device in the differential pressure flow meter?

• The main differential pressure generating devices are the orifice plate, venturi tube, flow nozzles, dall tubes, and elbows.

### Question 5: How does a differential pressure flow meter work?

• In a differential pressure flow meter, a pressure-generating device generates a differential pressure in the line. This differential pressure is given to the transmitter which will produce an output that is proportional to the flow flowing through the line.

### Question 6: What are the types of orifice plates?

• Concentric type Orifice Plate, Eccentric type Orifice Plate, Quadrant Edge Orifice Plate, and Segmental type orifice plate

### Question 7: What is the Beta Ratio for an orifice plate?

• The beta ratio for the orifice is the ratio between the orifice internal diameter and the pipe’s internal diameter.

### Question 8: What is the value of the Beta Ratio for an orifice plate?

• The beta ratio is kept from 0.3 to 0.75

### Question 9: What will happen if the Beta Ratio for an orifice plate is too low or too high?

• If the Beta ratio is too low, then the flow will face a high-pressure drop. If the Beta Ratio is too high then the DP generated will be too low.

### Question 10: How to install DP type Flow transmitter in the gas line?

• For a gas line, DP type Flow transmitter is installed above the line. This is done to avoid condensation coming into the impulse tube.

### Question 11: How to install DP type Flow transmitter in a liquid line?

• For a liquid line, DP type Flow transmitter is installed below the line. This is done to avoid bubbles coming into the impulse tube.

### Question 12: What is the relationship between the flow and the differential pressure in the differential pressure flow meter?

• The flow is proportional to the square root of the Differential Pressure

## Question 13: How does a turbine flow meter work?

• Whenever the liquid enters through the inlet of the turbine flow meter, the shaft of the turbine blades rotates which cuts the magnetic pickup. The magnetic pickup assembly produces the voltage which is proportional to the flow of the fluid flowing through the turbine flow meter.

### Question 14: What is the output of a turbine flow meter?

• The turbine flow meter produces pulses when a known or defined quantity of fluid passes through it.

### Question 15: On which principle does a magnetic flow meter work?

• The magnetic flow meter works on the principle of Faraday’s Law. In a magnetic flow meter, the field coils generate a magnetic field across a given area in the pipe. Two electrodes are placed at two opposite ends to pick up the voltage generated by the moving liquid. The voltage generated is proportional to the flow of the flowing liquid.

### Question 16: What is the limitation of the magnetic flow meter?

• A magnetic flow meter will only work for the liquids whose conductivity is above 5 micro siemens/centimeter because a liquid having conductivity below 5 micro siemens/ centimeter will not generate enough amount of voltage while passing through a magnetic field. Also, the pipe should be full while measuring the flow. Flow through half or partially filled pipe cannot be measured accurately.

### Question 17: How does an Ultrasonic flow meter work?

• In an ultrasonic flow meter, two trans receivers are installed in a pipe on opposite sides. The time of flight is calculated for both directions i.e. for downflow as well as up flow. Then according to the simple formula of speed = distance/time, we can calculate the speed as we know the distance and the time using the microprocessor.

### Question 18: What are the types of Ultrasonic flow meters?

• Time Transit Ultrasonic flow meter and Doppler Effect Ultrasonic flow meter are the two types of ultrasonic flow meters.

### Question 19: What is the difference between Nm3/hr vs m3/hr?

• Nm3/hr is the unit used for gas flow measurement where N is Normal which denotes standard temperature and pressure conditions. m3/hr is the unit used for liquid flow measurement.

### Question 20: What is the totalizer used for the flow meter?

• The totalizer is a type of counter which keeps a record of the amount of total flow passed.