Overview: The article explains current probe types, features, and applications for electrical diagnostics. It highlights Tektronix's advanced solutions for safe and accurate measurements.

Measuring electrical current is an essential part of electronics and electrical engineering work. Current probes are important tools that enable accurate current measurements in various applications ranging from automotive diagnostics to advanced electronics testing.

What Is a Current Probe?

A current probe is a specialized electronic device designed to measure the electric current flowing through a conductor, often with or without direct electrical contact or circuit interruption.

Types of Current Probes

Current probes are classified based on their sensing principles and measurement capabilities. The most common types include:

Shunt (Sense Resistor) Probes

These use a precision resistor placed in series with the circuit. The voltage drop across the resistor is measured and, using Ohm's law, converted to a current value. This is one of the traditional methods, which is direct and accurate for both AC and DC currents, but is invasive since it requires breaking the circuit. They can be troublesome and dangerous, particularly with stronger currents. The extra connection points can create unwanted voltage drops that affect measurement accuracy, and shunts often produce heat as a side effect.

Clamp-on Current Probes:

These clamp probes are non-intrusive and clamp around a conductor to sense current flow, as shown in Fig. 1. Many clamp-on probes use a current transformer principle, making them suitable for AC measurements. Some advanced clamp-on probes combine current transformer and Hall effect technologies to measure both AC and DC currents.

Keysight N2780B Series AC/DC Current Probes (N2783B, N2780B, N2781B, and N2782B current probes (from left to right)).

Fig. 1 Keysight N2780B Series AC/DC Current Probes (N2783B, N2780B, N2781B, and N2782B Current Probes (From Left to Right)). Source: Keysight

Working Principle

These probes provide a non-contact method for measuring electrical current. Unlike traditional techniques, they don\'t require opening or altering the circuit - operators simply place a clamp around the wire carrying the current to be measured. These probes detect the electromagnetic field generated by electricity flowing through the conductor.

This process works because of Faraday's law, which shows that changing magnetic fields can create voltage. The clamp in a current probe contains either a magnetic core (typically made from materials like ferrite or microcrystalline alloys) or a Hall effect sensor. When current passes through the clamp's jaws, it creates a magnetic field that produces a voltage signal.

This signal travels to a connected device such as an oscilloscope or digital multimeter (DMM) to display the current measurement. Since oscilloscopes display voltage over time, the current probe converts the detected current into a corresponding voltage signal for proper display.

Hall Effect Probes:

These employ a Hall effect sensor to detect the magnetic field generated by current flow, allowing for measurement of both AC and DC currents. Hall effect probes are widely used for their versatility and non-intrusive operation.

Rogowski Coil Probes:

These use a flexible, air-cored coil to sense the changing magnetic field around a conductor. Rogowski coils are excellent for measuring high-frequency AC or pulsed currents and are non-intrusive, but they cannot measure DC current.

Each type of current probe has its own strengths and is chosen based on the required measurement range, frequency response, and whether AC, DC, or both types of current need to be measured.

Key Parameters for Current Probe Measurements

  • Bandwidth determines the frequency range for accurate measurements, important for fast-switching current analysis.

  • Current range specifies minimum and maximum measurable values (DC, RMS, Peak), typically ranging from microamps to 2000 A, depending on the model.

  • Insertion impedance represents the impedance the probe adds to the circuit, which can affect current and voltage waveforms in bulky probe designs.

  • Current probes need zero calibration to eliminate measurement errors from temperature variations and environmental factors during no-current conditions.

  • De-skew compensates for timing differences between current and voltage probes during power measurements, ensuring accurate waveform alignment.

  • Demagnetization removes residual magnetism from ferromagnetic cores > that can cause measurement errors after measuring switched > currents.

Applications

Current probes can measure either direct current or alternating current, or both, based on their specific design and technology. During the development and testing of power supplies, motor drives, and inverters, these probes provide current waveform analysis while maintaining uninterrupted circuit operation.

They also serve an important function in diagnostic, troubleshooting, and maintenance operations. They are the most essential measurement instruments in electromagnetic compatibility (EMC) testing, particularly for conducted electromagnetic emission measurements.

Tektronix's Advanced Solutions for Safe and Accurate Measurements

Tektronix current probe solutions deliver measurement capabilities with the industry's widest selection of AC/DC and AC-only probes. These instruments provide exceptional accuracy across an extensive range from microamps to 2000 amperes, featuring 120 MHz bandwidth and industry-leading sensitivity down to 1 milliamp.

As the only current probes with third-party safety certifications (UL, CSA, ETL) and bare wire voltage ratings, they ensure maximum operator safety. This article elaborates on one such effective current probe series Tektronix TCP300 and TCP400 Series, as shown in Fig. 2. They are advanced AC/DC current measurement systems designed to provide precise and reliable current measurements for a wide range of applications.

Current probes (TCPA300, TCP312A, TCP305A, TCP303, TCPA400, TCP404XL) for AC/DC Current Measurement Systems.

Fig. 2 Current Probes (TCPA300, TCP312A, TCP305A, TCP303, TCPA400, TCP404XL) for AC/DC Current Measurement Systems. Source: Tektronix

  • TCPA300: Supports TCP303, TCP305A, TCP312A

  • TCPA400: Supports TCP404XL

These probes offer both AC and DC measurement capabilities, with bandwidths extending from DC up to

  • 100 MHz (TCP312A with TCPA300 amplifier)

  • 50 MHz (TCP305A)

  • 15 MHz (TCP303)

  • 2 MHz (TCP404XL with TCPA400 amplifier)

They support maximum DC current ratings of

  • 30 A (TCP312A)

  • 50 A (TCP305A)

  • 150 A (TCP303)

  • 750 A (TCP404XL, with 500 A continuous rating)

The probes feature automatic scaling and on-screen readout when connected to compatible Tektronix oscilloscopes, minimizing manual calculations and reducing the risk of measurement errors, as shown in Fig. 3. This allows for easy and non-intrusive connection to circuits, while low insertion impedance ensures minimal loading on the device under test.

Diagrammatic illustration of the current measurement system.

Fig. 3 Diagrammatic Illustration of the Current Measurement System. Source: Tektronix

Accuracy is high, with typical DC accuracy within ±3% of reading, and even better (±1%) for low current ranges at lower frequencies. The probes are equipped with status indicators for degaussing, probe open, overload, and other conditions and are certified for safety by third-party agencies.

These features make the TCP300 and TCP400 Series highly effective for accurate, safe, and convenient current measurements in laboratory and industrial environments.

Summarizing the Key Points

  • Current probes provide safe, accurate measurement of AC/DC currents with different sensing technologies, like the Hall effect, Rogowski coils, and clamp-on designs, suitable for various applications.

  • Tektronix offers a wide range of current probes with high bandwidth, safety certifications, and features like automatic scaling, ensuring precise and reliable measurements in diverse environments.

  • Clamp-on probes allow contactless current measurement by clamping around conductors, ideal for troubleshooting and maintenance without circuit disruption, utilizing electromagnetic principles.

  • The choice of current probe depends on parameters such as bandwidth, > current range, and insertion impedance, which directly affect > measurement accuracy and circuit loading effects.

Reference

Oemsecrets. (n.d.). N2783B Keysight Technologies Prices & Inventory - Test Leads & Test Probes, oemsecrets.com. https://www.oemsecrets.com/details/n2783b

Oemsecrets. (n.d.-b). TCP312A - Compare distributor prices & inventory, oemsecrets.com. https://www.oemsecrets.com/compare/TCP312A

Li, K., Videt, A., & Idir, N. (2014). Using current surface probe to measure the current of the fast power semiconductors. IEEE Transactions on Power Electronics, 30(6), 2911--2917. https://doi.org/10.1109/tpel.2014.2373400

Miao, S., Wanxiu, T., Gang, S., Xiaotong, M., Baoying, S., Jilei, S., & Dongxiang, L. (2018). A novel broadband High sensitivity current probe design and analysis for conducted emission testing. IOP Conference Series Earth and Environmental Science, 186, 012006. https://doi.org/10.1088/1755-1315/186/3/012006

Oscilloscope Current Probes & Clamps. (n.d.). Tektronix. https://www.tek.com/en/products/oscilloscopes/oscilloscope-probes/current-probes

AC/DC current measurement systems. (n.d.). Tektronix. https://www.tek.com/en/datasheet/ac-dc-current-measurement-systems

RIGOL. (2017, October 17). Current probes [Video]. YouTube. https://www.youtube.com/watch?v=wegyRCjfT7w

Rohde & Schwarz. (2023, September 6). Understanding current probes [Video]. YouTube. https://www.youtube.com/watch?v=U2LJJ8SgxwM