Analog Instruments Classification

Analog Instruments

• Analog instruments are devices that measure physical quantities, such as pressure, voltage, and current, and display the output in a continuous signal.
• These instruments are extensively used in various applications, including engineering, physics, and chemistry.

Classification of Analog Instruments

• Analog instruments can be classified into three types based on their function:
  • Indicating instruments: These instruments measure the magnitude of a quantity and display the output using a dial and a pointer. Examples include voltmeters, ammeters, and wattmeters.
  • Recording instruments: These instruments record the variations of a quantity over a specific period. Examples include recording voltmeters and oscilloscopes.
  • Integrating instruments: These instruments totalize events over a specific period. Examples include ampere-hour meters and watt-hour meters.

Deflection, Controlling, and Damping Torques

• Deflection torque: The torque required to deflect the pointer of an instrument to a specific position. It is produced by the deflecting system.
• Controlling torque: The torque that opposes the deflection torque and brings the pointer back to its zero position. It is produced by the controlling system.
• Damping torque: The torque that reduces the oscillations of the pointer and helps it to settle quickly. It is produced by the damping system.

Effects Used to Produce Deflecting Torque

• Magnetic effect: Used in most ammeters, voltmeters, and wattmeters. It produces a deflecting torque by using a magnetic field.
• Electromagnetic induction effect: Used in voltmeters, ammeters, and energy meters. It produces a deflecting torque by using electromagnetic induction.
• Heating effect: Used in thermal instruments. It produces a deflecting torque by using the heat generated by the current.
• Chemical effect: Used in integrating instruments. It produces a deflecting torque by using a chemical reaction.
• Electrostatic effect: Used in electrostatic instruments. It produces a deflecting torque by using an electrostatic field.

Torque to Weight Ratio (T/W Ratio)

• The T/W ratio is an important factor in instrument design. It is the ratio of the deflecting torque to the frictional torque.
• A higher T/W ratio indicates a more sensitive instrument.

Analog Voltmeters and Ammeters

• Analog voltmeters measure voltage and display the output using a needle.
• Analog ammeters measure current and display the output using a needle.
• Both types of instruments use a moving coil or a moving iron to measure the quantity.

Comparison with Digital Instruments

• Analog instruments have some advantages over digital instruments, such as:
  • Providing a better idea of the order of magnitude and trends.
  • Not requiring a power supply beyond the test current source.
• However, digital instruments have generally superseded analog instruments due to their superior accuracy and precision.

Scale and Range

• Analog instruments have a scale and range that is determined by the instrument's design.

• The scale and range can be altered by providing a shunt coil or a multiplier.### Merits and Demerits

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Examples of Merits and Demerits

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