Provide a convenient way of current measurement

The current probe is designed to provide a convenient way to measure current. They can be AC coupled, using current transformer technology or AC/DC coupling. Regardless of the type, the probe includes a split core geometry to facilitate the installation of current-carrying conductors without the need to disassemble them. Teledyne LeCroy CP030 is a typical example of AC/DC current probe, which can measure 30 A current with a bandwidth of 50 MHz (Figure 3).


Figure 3: Teledyne LeCroy CP030 is a 30 A, DC-50 MHz current probe. It uses the ProBus interface and can be fully integrated with Teledyne LeCroy oscilloscopes. (Photo: Teledyne LeCroy).
CP030 uses hybrid technology, while using Hall-effect devices for DC and low-frequency AC signals and current transformers for high-frequency AC signals (Figure 4).


Figure 4: CP030 AC/DC current probe functional block diagram. (Photo: Digi-Key Electronics)
CP030 uses a separate ferrite core, which can be quickly inserted into the wire carrying the current to be measured. It adds a Hall-effect sensor and feedback winding in the gap of the magnetic core. The Hall-effect sensor can generate an output current proportional to the magnetic flux in the magnetic core when a reasonable bias is applied. This output can be amplified to drive the feedback winding, so that the magnetic core becomes a state of zero magnetic flux. At this time, due to the current-carrying wire, the current through the feedback winding is proportional to the magnetic flux. The output termination converts this current into voltage. Since the output of the Hall-effect sensor decreases as the frequency increases, the feedback winding acts as a current transformer, so the high-frequency part of the measured signal can be accurately measured. The sensitivity of CP030 is 1 V/A. The probe transmits this information to the oscilloscope through the ProBus interface. The oscilloscope automatically adjusts the ratio of the channel inserted into the probe to read the ampere value (Figure 5).


Figure 5: Teledyne LeCroy HDO 4104 oscilloscope channel setting connected to CP030. The probe will be automatically identified and shown in the "Probe" input box. The correct ratio is automatically entered into the "Units/V" input box, and the vertical unit is set to "Amperes". (Photo: Digi-Key Electronics)