The most common approach to current measurement on oscilloscopes is to use current transformers, Rogowski coils or Hall effect clamp-on probes. High-quality magnetic probes are accurate when used within their specifications. They are also convenient when current is flowing in wires or test loops, since they do not require breaking the circuit. However, they have some intrinsic limitations.
These are explained in a recent presentation by Yogesh Pai, product manager at Tektronix, whose company has just introduced a completely galvanic isolated probe optimized for making shunt-based current measurements. The new IsoVu Current Shunt Probe is the world’s first to utilize RF isolation, delivering exceptional precision and safety when measuring fast-changing current across both low and high-voltage systems.
Magnetic probes require a loop of wire to make measurements, he notes. “Such a loop may not be possible due to physical constraints or circuit sensitivity. Due to the nature of magnetic materials, bandwidths are limited to around 100 MHz, even for a high-end clamp-on current probe. And although it may be tempting to assume that a non-contact probe does not impact circuit performance, many engineers have been confused by the unexpected impact of the insertion impedance of a magnetic probe, which can be close to 1 Ω at full bandwidth.”
IsoVu probes are optimized specifically for making current measurements using shunt resistors, even when they are floating above ground and subjected to significant common mode voltage signals. High bandwidth is a key feature. Unlike transformer, Rogowski or Hall effect current probes, TICP current probes enable measurements from DC to hundreds of MHz, when paired with high-performance shunts or CVRs (current viewing resistor). Complete RF isolation between the probe tip and the scope eliminates ground loops and helps deliver extraordinary common mode rejection (CMRR) of up to 90 dB at 1 MHz to dramatically reduce common mode noise.
TICP IsoVu probes are the industry’s first current shunt probes to use RF isolation, providing complete galvanic isolation between measurement systems and devices under test, says the company. Available in bandwidths up to 1 GHz, they enable engineers to capture accurate measurements of fast-changing currents on their oscilloscopes across a wide voltage range in nanoseconds – from microamps to kiloamps.
“The wide measurement range covers previously inaccessible high-voltage environments, from fast-switching SiC and GaN power converters to low-power applications like battery performance testing in mobile devices – all with a single probe,” said Daryl Ellis, Tektronix’s general manager of Entry and Mainstream Portfolio. See www.tektronix.com.
