Abstract: A flowmeter sometimes called ultrasonic, but sometimes not ultrasonic including two phase locked loops, a portion of each of which form a common path through amplifiers, an electronic attenuator with automatic gain control, a pulse detector, and a pulse or phase comparator. The pulse comparator, through switches, controls first and second voltage controlled oscillators on a time shared basis. First and second counters are connected from the first and second voltage controlled oscillators, respectively. The first and second counters supply transmission pulses to submerged first and second facing transducers, respectively, at different times. The voltage controlled oscillators are always driven until a later counter pulse coincides with a corresponding received pulse. Time sharing is, in part, accomplished by beginning energy propagation in opposite directions at successive times and before either pulse is received.

Abstract: An electro-chemical sensor for the measurement of concentrations of gas or vapor in accordance with the limiting current principle and comprising an electrolytic cell having a sensing electrode, a counter electrode and an intervening body of electrolyte and also a restriction to the rate of access of gas or vapor to the sensing electrode. The improvement comprises said restriction being in the form of a gas-phase diffusion barrier including at least one narrow passage for the diffusion of gas. The gas-phase diffusion barrier may be in the form of a porous body, of which the permeability of the body may be more than twenty times greater than the diffusibility, but is preferably less than ten times the diffusibility and more preferably not more than 10% greater than the diffusibility. Alternatively the gas-phase diffusion barrier may be defined by a capillary. The capillary may be of plastics material and may be enclosed within an outer metal sheath of lesser co-efficient of expansion.