Internal resistance is a critical factor in coil design and can have a significant impact on performance. Testing for internal resistance is simple and can be done using a multimeter. To test for internal resistance, first determine the coil’s diameter. Next, measure the coil’s resistance using a multimeter while applying a known current (usually 10 or 20 mA) to the coil. The resulting reading should be in ohms. If the reading is higher than 1,000 ohms, then the coil has an internal resistance and should not be used in applications requiring high performance. If the reading is lower than 1,000 ohms, then the coil may have an internal resistance that needs to be taken into account when designing a circuit. ..
