Magnetic flow meter:

·         Magnetic flow meter is based on faradays law of electromagnetic induction.

·         For early magmeters, 1-5 microsiemens per centimeter minimum fluid conductivity required for their operation. But newer design required between 0.05 and 0.1 μs/cm.

·         A conductive fluid flows through a pipe of diameter (D) through a magnetic density (B) generated by the coils, the amount of voltage (E) develops across the electrodes (faradays law) will be proportional to the velocity(v) of the liquid.

·         The magnetic field density and the pipe dia are fixed values, they can be combined into a calibration factor (K)

E=KV

·         Magmeter can measure flow in both directions, as a reversing direction will change the polarity but not the magnitude of the signal.

·         The electrodes develops millivolt signal, this signal is typically converted into (4-20ma) or frequency output (0-10,000Hz)

·         Magmeter signal is a weak one, the lead wire should be shielded and twisted if the transmitter is remote.

·         The magmeters coils can be powered by either AC or DC.

·         AC  powered produced sine wave. The main problem with AC magmeter design in that noise can vary with process conditions and frequent rezeoring is required to maintain accuracy.

·         DC powered magmeter produced pulse waves,  a low frequency (7-30Hz) dc pulse is used to exite the magnetic coils in between the pulses, the transmitter sees only the noise signal. Therefore the noise can be continuously eliminated after each cycle. (eliminate zero shift)

·         DC powered magmeter, addition to being more accurate and able to measure lower flows, it is less bulky, easier to install, use less energy and having lower cost than AC meters.

·         Its accuracy does not depend on viscosity since its measure by volume. So it can be used for highly viscous, slurries or liquids with varying viscosities.

·         Liner material used for: - hard rubber, soft rubber, PTFE, PFA and ceramics.

·         Common electrode materials are stainless steel 1.4571, 1.4539, hasteloy, tantalum and platinum.