Application of MR element to clamp-on type current meter.
M. Matsumoto, T. Haeiwa, H. Inoue, Souta TANAKA · Journal of the Magnetics Society of Japan · 1991
A new clamp-on type current meter with magnetoresistive (MR) element has been built which has the sensitivity of sub-milli ampere order and wide frequency bandwidth. The sensor element is a 1000∼1500Å thick, 0.2 mm wide, 15 mm long, evaporated thin film of 80/20 NiFe with 2.5% magnetoresistivity. The MR element is installed in the 0.2 mm gap of ferrite core which has a 188-turn coil to provide dc bias field (4 Oe) for linear sensitivity and to be used for feedback detection. In non-feedback mode, system noise level (sensor+circuit) is 0.8 mV which is equivalent to 0.2 mA current. In feedback mode, this current meter maintains a linear sensitivity throughout 0.4A in the frequency range of DC∼10 kHz. The temperature stability is improved by compensating with double elements.