Understanding High Resistance Measurement Methods

The question asks to identify the appropriate method for measuring high resistance, specifically resistances above 100kΩ. Different methods are used for measuring resistance depending on the range of resistance being measured.

Let's look at the common methods mentioned:

• Megger Method: A Megger, also known as an insulation resistance tester, is specifically designed to measure very high resistances, such as the insulation resistance of cables, motors, and transformers. These resistances are typically in the megaohm (MΩ) range or higher. A Megger applies a high DC voltage (often 500V, 1000V, or more) across the resistance being measured and measures the resulting small current to determine the resistance. This method is ideal for resistances above 100 kΩ.
• Ohmeter Method: Standard ohmmeters are generally suitable for measuring low to medium resistances (from a few ohms up to several hundred kilohms). They might not be accurate or capable of measuring resistances in the megaohm range effectively, especially when dealing with potential leakage currents or other factors at high resistance values.
• Potentiometer Method: This method is primarily used for comparing potential differences or electromotive forces (EMFs). While it can be used in some resistance measurement setups (like comparing unknown resistance to known resistance using a bridge circuit principle), it is not the standard or most practical method for directly measuring a high resistance value like 100 kΩ or more.
• Wheatstone Bridge Method: The Wheatstone bridge is a precise method for measuring unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. It is most accurate for measuring medium resistances. While variations exist, the standard Wheatstone bridge is less suitable for accurately measuring extremely high resistances compared to a Megger.

Based on the characteristics of these methods, the Megger method is the most appropriate and widely used technique for measuring high resistances, particularly those exceeding 100 kΩ.