Precise AC & DC Current Measurement With Zero-Flux Technology.

At the core of every Zero-Flux transducer is a measuring head built around toroidal-wound ring cores. The primary current (Ip) generates a magnetic flux, which is immediately counteracted by a secondary current (Is) flowing through the secondary winding (Ns). Any flux that remains is sensed by three toroidal cores inside the measuring head:

Two DC-sensing cores (N1, N2) detect any remaining DC flux. An oscillator drives these cores into saturation in opposite directions, producing current peaks that are equal in both directions whenever the residual DC flux is zero. If it isn’t zero, the difference between the peaks is proportional to that residual flux. One AC-sensing core (N3) captures the AC component of the remaining flux.

A peak detector isolates the residual DC flux. Once the AC component is added back in, a closed control loop drives a power amplifier, which feeds a secondary current (Is) into the winding — precisely the current needed to bring the flux back to zero. Because this secondary current is a scaled image of the primary current, it can be converted into a clean, accurate output signal.

Above a few kilohertz, the power amplifier no longer actively regulates the output and effectively forms a short circuit; the measuring head then continues to perform as a passive current transformer. This extends the usable bandwidth from DC all the way to the megahertz region, limited only by the stray reactance and capacitance of the head and its cable.

vs. conventional current transformers (CTs): CTs cannot measure DC and distort or lose low-frequency signals, since they saturate without an active compensation current. Zero-Flux transducers measure accurately from true DC up into the MHz range, with no saturation and no waveform distortion.

vs. shunt resistors: Shunts sit directly in the current path, causing power loss (I²R heating) and offering no galvanic isolation between the measured circuit and the measuring electronics. Zero-Flux transducers add negligible insertion loss and provide full galvanic isolation, protecting sensitive measurement and control electronics.

vs. Hall-effect sensors: Hall sensors are prone to offset drift, temperature sensitivity, and limited linearity, since they measure flux passively. The active, closed-loop compensation of the Zero-Flux principle continuously drives the flux back to zero, delivering markedly higher accuracy and long-term stability — without relying on temperature-controlled hardware.