Abstract: There is described a fluid flow sensor (10)for sensing a flow (F) of a fluid (120) through a region. The sensor (10) comprises a magnetic circuit (50, 60a, 60b) for applying a magnetic field (70) to the region, and electrodes (40a, 40b) for sensing a potential (V) generated in operation between the electrodes (40a, 40b) in response to the fluid (120) flowing through the magnetic field (70). Each electrode (40) includes a metal element (130; 300; 400; 500), a metal halide element (110; 310; 320; 410; 520), and an electrically conductive porous element (100; 330; 420; 530). The porous element (100; 330; 420; 530), hinders progressive loss of the metal halide element (110; 310, 320; 410; 520), to the flow (F) and provides an electrically conductive path between the flow (F) and the metal halide element (110; 310; 320; 410; 520), and thereby to the metal element (130; 300; 400; 500).

Abstract: A magnetic transducer (109) for measuring the flow of a fluid (108) has electrodes (102) and an alternating magnetic field (107), an electrode (102) having lower noise energy at frequencies below 5 Hz than an electrode comprising carbon or corrosion-resistant metal alloy. The noise characteristic of the electrode (102) at magnetic field frequencies around 1 Hz is lower than that of an electrode comprising carbon or corrosion-resistant metal alloy.