• Cameras have tiny transducers that measure a subject's distance.photo camera image by A74.FR Ben Fontaine from Fotolia.com
  
  A transducer is a device that converts one form of energy to another, usually as a transmitter, receiver or sensor. Different kinds of transducers use different forms of energy such as sound, light and electricity to make visual signals, sense movement and measure forces. In many instances, transducers are used to make equipment safer. A light sensor can, for example, sense the presence of a person's hand and switch off dangerous machinery.
  
  

Position Measurement

• An ultrasonic transducer measures the distance to an object by sending out pulses of high-frequency sound and processing the echoes that bounce back. They can measure distances from a few inches to over 100 feet in a fraction of a second. This method is suitable for measuring the distance along an unobstructed path to any object more than a few inches in size. Measuring systems use computer software to track position, velocity and acceleration based on these signals.
  
  

Proximity Detector

• Though related to measuring distance, a proximity detector has a slightly different job: it senses if an object is close. Hall-Effect transducers are frequently used for proximity detection, as they are inexpensive, are easy to use, and have no moving parts. The Hall Effect creates a small voltage in materials in the presence of a magnetic field. This has some important advantages: an object doesn't have to be touching the transducer to be detected and it can detect anything that may have a small magnet attached to it. The solid-state nature of Hall-Effect transducers means that they can sense thousands of proximity changes per second and operate for years without wear.
  
  

Force Measurement

• Strain gauges are transducers that measure mechanical forces through resistance changes in fine wire. Though the amount of resistance change is small, sensitive electronic circuits can translate the change into accurate force measurements. Computerized systems can read these changes and provide information on force, weight or pressure. Strain gauges are highly accurate and repeatable--several measurements of the same weight will give very nearly the same results.
  
  

Sound

• Loudspeakers also fit the definition of transducers. They convert electrical energy into small movements that make sound. Most loudspeakers are made of a thin cone of material, such as paper or plastic, attached to a wire coil. A strong magnet sits near the coil, so when electric current flows through the coil, magnetic forces make the cone move back and forth. If this movement is at audio frequencies, it produces sound. The basic design works for a wide range of sizes, from tiny ear buds to large theater speakers.