An electric circuit board has a current trace thereon and a notch in the edge and an opening therethrough on opposite sides of the trace. A magnetic sensor is retained in the opening; and a flux member retained by the notch and opening forms a magnetic circuit around the current trace to concentrate current induced flux through the magnetic sensor. The flux member is made of a ductile magnetic material and is therefore easy to manufacture and handle without breakage compared to prior art ferrite flux members. It is also resilient so as to permit a "snap-on" design for ease of assembly with positive retention of the flux member on the board and of the magnetic sensor within the opening with minimal series air gap. The flux member further has high internal eddy current and hysteresis losses for inherent high frequency filtering to reduce aliasing distortion in sensor output to digital apparatus when applied to a measurement of PWM motor current.