Abstract: A magnetic sensor is disclosed which features an arrangement that relies upon the principle of a fixed, non-pendulous magnetic sensing device (2), which is rendered insensitive to the effect of the earth's vertical magnetic field component by means of an adjacent cooperating magnetic member (20) pendulously-supported to maintain its axis along the true vertical. Means (34, 44, 46, 48, 50) are disclosed whereby the magnetic field provided by the pendulously-supported magnetic member is automatically adjusted to cancel the earth's vertical field even when the latter changes for any reason.

Abstract: An acoustic fluid velocity measuring system includes mutually perpendicular arms disposed in the direction of the rectangular components of the fluid velocity, with each arm supporting two transmitting and two receiving electro-acoustic transducers. Pulses of ultrasonic energy are transmitted and received in and against the direction of fluid flow. The transducers in each arm are arranged in separate electrical loops, each of which provides an output at a different frequency. The frequencies are compared to measure fluid speed and direction which appear on a digital display. The measurements are independent of ambient temperature and the transducers are heated so that the system operates under ice forming meteorological conditions.