Choosing the Right Current Probes

PowerSight offers a wide selection of current probes for just about every need. The one downside of having so many options is deciding on which current probe is the right one for the job, and how many to get. Below, is a discussion of the various current probe technologies and their trade-offs to consider when making the best choice (or a compromise choice) for current probes. For a quick answer, without doing reading, you can take our quick 3-question quiz to find a good choice for your needs.

If you need to rent or purchase a power analysis system, they come with eFX6000 probes by default because the eFX6000 covers most all situations, but you can fully customize any system to include the probes and accessories you choose. All PowerSight current probes are universally compatible with PowerSight analyzers, meaning any probes can work with any analyzer.

Current Probe Technology

There are 3 different technologies used for measuring current with PowerSight:

Clamp-on (and Toroid)

Clamp-on technology is the oldest technology for measuring current. It basically consists of iron core jaws with wire wound around a section of the jaws. When the jaws close around a conductor, it effectively forms a transformer with 1 winding in the primary (the conductor you clamp around) and however many windings are in the secondary to boost the magnetic field. These types of probes can be very cheap or very expensive; it largely depends on the core material. Cheap ones can exhibit bad linearity (poor accuracy of amps readings over the measurement range), excessive phase shift (which lowers the accuracy of power readings), and limited frequency response (which under-reports harmonics and the amps flowing in non-linear loads).
PowerSight clamp-ons (our High Accuracy, HA series) use high quality silicon steel for their core material to obtain the best in linearity, phase shift, and frequency response. Generally, the lower the current you need to measure, the phase shift and frequency response degrade somewhat and the price increases. Our highest accuracy probe is the HA1000, for high accuracy measurement from 1 to 1,000 amps AC. It costs $295. Our lowest measuring probe is the HA-GFD, which measures down to 0.005 amps AC but costs $845. It is worth noting that for monitoring office equipment (typically very low current), our 120ADP offers an economical and non-invasive method for measuring current and power.

Rogowski (rope-type)

Rogowski coils are a different technology where wire is wound around the full length of an insulating material. When the coil is wrapped around a conductor, current is induced into it proportional to the change in the current (i.e. the differential of the current waveform). This output is run into an integrator circuit to recover the original waveform (i.e. the integrated differential waveform). It is the most recent current measuring technology and the most popular. People love them because they are flexible, thin, and can be quite long. Flexibility helps in fitting in just about any panel situation. Being thin counts when trying to slip the rope between two rigid conductors that are close together. Being long allows wrapping around the largest bus bar. It also allows wrapping around all 3 phase conductors to detect large leakage current. Anyone who uses Rogowski type current probes appreciates this flexibility and ability to work in just about any situation. That’s why the eFX6000, with two ranges covering from 1 to 6000 amps AC, is our overwhelming favorite.

However, Rogowski coils have their drawbacks. Chief among them are accuracy issues. Manufacturers state very good accuracies for Rogowski coils, but there are several significant qualifiers.

First of all, the position of the coil when wrapped around a conductor matters. Typically, the coil measurements can vary +/-2% depending on the position of the probe around a conductor. This means that a 1% stated accuracy probe may be a 3% accuracy probe when installed. For this reason, PowerSight probes are calibrated at a specific orientation, the cable hanging at the 9 o’clock position. If you match that orientation, you should achieve the 1% state accuracy of the probe.

The Rogowski coil is only as good as the integrator that it is hooked up to. The right integrator will give good linearity, phase shift, and frequency response (see discussion of clamp-on probes). Cutting corners results in the loss of accuracy that low quality clamp-ons suffer from.

Finally, our experience is that Rogowski current probes require calibration more than clamp-on types. Typically, they really need to be calibrated every year. Fortunately, our (extendable) deluxe warranty includes annual calibration for the analyzer and current probes.

Hall Effect

As discussed previously, clamp-on and Rogowski probes measure the changing magnetic field that results from an AC current. Since a DC current has no changing field, those technologies cannot measure a DC current. Hall effect probes have sensors that measure the intensity of the magnetic field due to current flowing. This technology can measure DC current. It can measure AC current as well. However, the technology is more expensive, less accurate, and requires “zeroing” before each use. For these reasons, it is best to rely on Hall effect for DC current, but to have a separate set of probes for AC measurements.