Electric current sensors

Electric current sensors (potential-free sensors, e.g., for alternators, electric motors, and starters or for battery power management in future 42-V systems). 

In 1998 the world market for electric-current sensors was 168 million Euro and it is expected to grow to about 260 million Euro by 2008. The automotive sector will contribute about 20% [1],... 

An active magnetic axial bearing consists of two stators and a rotor disk (Figure 6-4). A sensor located at the end of the shaft monitors and maintains the rotor position between the two stators. The principle of operation is the same for both axial and radial bearings any deviation from the normal position of the rotor is communicated to the electronic control system, which adjusts the electric current going to the electromagnets to correct the rotor position. 

The hot-wire anemometer sensor is a very fine wire with a diameter of few micrometers and length of few millimeters. This wire is connected to a measurement bridge and an electrical current is fed through the wire. The wire is heated to a temperature above the air temperature and the air velocity is determined by the cooling effect of the wire. The voltage over the wire, U, is a function not only of the velocity but also of the excess temperature and the fluid properties in the following way ... 

The other limit is the problem of temperature measurements. Classical temperature sensors could be avoided in relation to power level. Hence, temperature measurements will be distorted by strong electric currents induced inside the metallic wires insuring connection of temperature sensor. The technological solution is the optical fiber thermometers [35-39]. However, measurements are limited below 250 °C. For higher values, surface temperature can be estimated by infrared camera or pyrometer [38, 40], However, due to volumic character of microwave heating, surface temperatures are often inferior to core temperatures. 

In general, an instrument consists of four components a sensor that converts a property of the solution into a weak electrical signal, a signal processor that amplifies or scales the signal and converts it to a useable form, a readout device that displays the signal for the analyst to see, and a power supply to provide the power to run these three components. The information flow within the instrument occurs with the movement of electrons, or electrical current. 

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