Instrument for Measuring High Resistance Explained

Understanding which instrument is suitable for measuring electrical resistance is crucial in electrical engineering and testing. Different instruments are designed for different resistance ranges. This explanation focuses on identifying the correct tool for measuring high resistance from the options provided.

Analyzing Resistance Measuring Instruments

Let's examine the purpose of each instrument mentioned:

• Wheatstone bridge: This is a classic circuit used for measuring an unknown resistance value by balancing two legs of a bridge circuit. It is highly accurate but typically best suited for measuring medium resistances, generally in the range of ohms to megaohms, but not specifically optimized for the highest resistance values (like insulation resistance).
• Kelvin's Double bridge: This bridge is a modification of the Wheatstone bridge. Its primary advantage is its ability to minimize and eliminate the effect of lead and contact resistances. Therefore, it is specifically designed and used for measuring very low resistances accurately, typically in the micro-ohm or milliohm range.
• Carey – Foster bridge: This bridge is often used for precise comparison of resistances or measuring resistance variations. While capable of measuring resistance, it's not the primary or most efficient instrument specifically designed for measuring extremely high resistance values compared to other options.
• Megger (Megohmmeter): A Megger is an electronic instrument used specifically for measuring very high electrical resistance. It typically employs a high-voltage DC generator (manual or electronic) to apply a voltage across the resistance being measured, allowing for accurate readings of insulation resistance, which can be in the megaohm ($M\Omega$) or gigaohm ($G\Omega$) range. This makes it the ideal instrument for testing insulation quality in electrical equipment.

Conclusion on High Resistance Measurement

Based on the functionalities, the Meggar is the instrument specifically designed and most commonly used for measuring high resistance, particularly insulation resistance.