Magnetic Flow Meters

Question 1

Explain Faradays law and how it relates to magnetic flow meters.

Answer 1

When a conductor moves through a magnetic field a voltage is generated that is proportional to the velocity of the conductor. In a magnetic flow meter the process is the conductor.

Question 2

Explain why the magnetic flow meter flow tube must be non-magnetic.

Answer 2

So that the magnetic field does not penetrate the tube walls bypassing the conducting fluid

Question 3

Explain why the liquid measured by a magnetic flow meter must have some minimal
conductivity.

Answer 3

So that the induced voltage can be measured

Question 4

Explain why the magnetic flow meter flow tube must be non-conductive.

Answer 4

To measure Voltage the probes can not be shorted out by the tube

Question 5

What is the purpose of the Teflon liner in a magnetic meter?

Answer 5

When the flow tube is made out of a metal compound a Teflon liner can be installed to prevent the probes from shorting out.

Question 6

Describe applications for magnetic flow meters.

Answer 6

Processes with a conductive fluid like pulp and paper, sewage water, or the food industry.

Question 7

Explain why coating of the electrodes on magnetic flow meters may cause errors and what
can be done to minimize this problem.

Answer 7

Some processes leave deposits in the pipes making the meter unreliable over time. Velocities can be kept higher, installation of removable electrodes, or a bullet shaped electrode design can be implemented to prevent coating.

Question 8

Explain why proper grounding is very important for magnetic flow meters.

Answer 8

Since the signal is a very low voltage electrical noise becomes an issue. Grounding prevents this.

Question 9

What are the problems with AC excitation?

Answer 9

1) Electrical noise is a problem
2) Needs to be re-zeroed to remove noise

Question 10

What are the problems with DC excitation?

Answer 10

Eliminates electrical noise but has a electrolysis problem

Question 11

Describe pulsed DC tri-states to measure flow

Answer 11

Eliminates electrical noise and electrolysis

Question 12

What is straight DC used for in measuring flow and what are it’s problems?

Answer 12

Used on fluids with high conductivity. Noise and electrolysis are still problems.

Question 13

What part of the magnetic flow meter must be non magnetic?

Answer 13

Flow tube of the meter

Question 14

What part of the magnetic flow meter must be non conductive?

Answer 14

The flow tube that is in contact with the fluid.