Abstract: A watthour meter or a wattmeter comprising Hall sensors and possessing a precise linearity of the conversion of low voltage into frequency within a broad dynamic range. The required linearity is achieved by providing a multiplication-adding circuit MS with a current output, to which the noninverting input of the last operational amplifier in the circuit is connected, by providing a current-frequency converter IFC with a differential integrator DI comprising an active compensation feedback circuit, by shunting the output and the input of the converter IFC by a compensation circuit CC to compensate the ripple, offset and charge injections of electronic switches, and by placing the Hall sensors so that the magnetic induction direction in the slits of a ferromagnetic yoke is different for each sensor of a pair of them.

Abstract: A device for measuring the resistivity of a conductive layer buried beneath an outer layer. The device is capacitively coupled to the buried layer by a driven electrode and a pickup electrode. An adjustable frequency source resonates the two electrodes with an inductor so that an attached meter measures the resistivity of only the buried layer.