There are three basic methods to make current measurements: shunts, transformers and Hall Effect devices. The next three slides give more details on each of these methods. Shunts can measure DC and AC currents up to reasonably high frequency. You can break a circuit to install a shunt (as shown on the next slide) or you can embed a shunt as a sensor in the circuit. Transformers can measure AC currents (but not DC). There are inexpensive AC current probes which incorporate transformers and measure only AC current. Hall effect devices are good for measuring DC current and can also measure low frequency AC. There are trade-offs for using each of the three techniques. The best types of general purpose current probes for use with oscilloscopes combine the use of transformers and Hall effect. They can detect DC current and have flat bandwidth response for detecting currents out to fairly high frequencies (up to 100MHz).