The Hall effect device is the most popular current measuring method. It has a magnetic core and a shunt is needed to clamp the current probe across. It does measure AC and DC; it is pretty easy to attach to the circuit, and the cost is moderate. The Hall effect probe is powered by the oscilloscope; this slide shows the little amplifier that is inside the probe. In some cases it may be necessary to add a shunt, an access wire, and it does insert some impedance into the circuit under test. A wider bandwidth current probe can be produced by combining a conventional current transformer with a Hall Effect device to measure DC. A passive filter circuit is added to the Hall effect amplifier to carefully control the upper bandwidth to align with the lower bandwidth of the current transformer, providing relatively flat frequency response from DC to moderate frequencies. As with the DC current probe, a silicon Hall effect device is generally used to reduce gain error over temperature. While they are moderate cost, these probes tend to have low sensitivity.