INTRODUCTION

The possibility of inducing voltages in liquids moving through magnetic fields was known by Faraday in 1832, but the first flowmeter-like device was reported by Williams in 1930. The first real advance in the subject came from the medical field where Kolin (1936, 1941) introduced many ideas that are now standard practice.

The industrial interest in electromagnetic flowmeters (sometimes referred to as EM or magnetic flowmeters) grew in the 1950s with

• the Tobiflux meter (Tobi 1953) in Holland for rayon viscose, sand and water, and acid slurries;

• Foxboro, to whom the patent was assigned in 1952;

• the first commercial instruments in 1954 (Balls and Brown 1959).

• nuclear reactor applications;

• the work that resulted in an essential book by J. A. Shercliff (1962).

In this chapter, we shall concentrate on the application of the flowmeter to fluids that are of low conductivity, such as water-based liquids (Baker 1982). The flowmeter has also been used with liquid metals (Baker 1969, 1970b, 1977), and a few designs have been built for use with nonconducting dielectric liquids (Al-Rabeh et al. 1978). The reader is referred to the original papers because space prevents their inclusion here. Three papers by Wyatt (1961, 1977, 1982), a pioneer in blood flow measurement research, are referenced for those interested.

OPERATING PRINCIPLE

We start with the simple induction, which occurs when a conductor moves through a magnetic field. Figure 12.1 shows a copper wire cutting the flux of a permanent magnet.