Which of the following is a non-contact instrument used in energy audit exercises for speed measurement? 

The correct answer is option 4):(Stroboscope)

Concept:

Stroboscope

• Stroboscope, instrument that provides intermittent illumination of a rotating or vibrating object in order to study the motion of the object or to determine its rotary speed or vibration frequency
• A stroboscope is an instrument used to make a cyclically moving object appear to be slow-moving or stationary.
• It consists of either a rotating disk with slots or holes or a lamp such as a flash tube which produces brief repetitive flashes of light.
• Usually, the rate of the stroboscope is adjustable to different frequencies. When a rotating or vibrating object is observed with the stroboscope at its vibration frequency, it appears stationary.
• Thus stroboscopes are also used to measure frequency.
• The principle is used for the study of rotating, reciprocating, oscillating, or vibrating objects. A stroboscope is also used to synchronize induction motors, to set the ignition timing of internal combustion engines is called a timing light. Machine parts and vibrating strings are common examples.
•  In any audit exercise speed measurements are critical as they may change with frequency, belt slip and loading. A simple tachometer is a contact type instrument which can be used where direct access is possible. More sophisticated and safer ones are non-contact instruments such as stroboscopes
• The stroboscope is a non-contact instrument used in energy audit exercises for speed measurement.