Measurement of Linear Velocity

TL;DR

Learn about the measurement of linear velocity using electromagnetic transducers, including their construction, working principles, advantages, disadvantages, and applications.

Transcript

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Key Insights

• 📏 Linear velocity is the velocity in a straight direction resulting from translational motion.
• 💱 Electromagnetic transducers measure linear velocity by detecting changes in output voltage generated by changes in flux linkages and reluctance.
• 🧲 Moving magnet and moving coil are the two categories of electromagnetic transducers based on whether the magnet or coil moves to change the air gap and reluctance.
• 🏑 Moving magnet transducers have negligible maintenance requirements and a linear measuring scale, but can be affected by stray magnetic fields and have limited frequency response.
• 🧲 Moving coil transducers have a reversed function of magnet and coil compared to moving magnet type transducers and are less affected by stray magnetic fields.
• 🕵️ Seismic type velocity transducers measure velocity by detecting vibrations and are connected to the vibrating object, but require connections to the moving object.

Questions & Answers

Q: How do electromagnetic transducers measure linear velocity?

Electromagnetic transducers measure linear velocity by detecting changes in the air gap and reluctance between a magnet or coil. These changes result in changes in output voltage, which is proportional to velocity.

Q: What are the advantages of moving magnet type transducers?

Moving magnet transducers have negligible maintenance requirements, a linear measuring scale, can be used as event markers, and are robust and inexpensive.

Q: What are the disadvantages of moving magnet type transducers?

Moving magnet transducers can be affected by stray magnetic fields, have limited frequency response, and are not suitable for measuring vibrations due to calibration deterioration caused by contact with steel tools.

Q: How do seismic type velocity transducers work?

Seismic type velocity transducers use a permanent magnet supported by springs and low friction bearing rings. When connected to a vibrating object at a frequency higher than its natural frequency, the magnet appears stationary, and oscillation of the coil and case generates an output voltage proportional to vibration amplitude.

Summary & Key Takeaways

• Linear velocity refers to the velocity in a straight direction, measured using electromagnetic transducers that work by measuring output voltage generated by changes in flux linkages and reluctance.

• There are two types of electromagnetic transducers: moving coil and moving magnet, distinguished by whether the magnet or coil moves to change the air gap and reluctance.

• Moving magnet transducers use a permanent magnet and a coil, with the magnet's movement causing a change in air gap length and reluctance, resulting in a change in output voltage that is proportional to velocity.

• Moving coil transducers have a stationary magnet and a moving coil, and the motion of the coil changes the air gap, reluctance, and output voltage, providing a measure of velocity.