![]() These transistors change their state when they are in the presence of a very low strength (on the order of 25 gauss) magnetic field. Instead of pick-up coils, Hall-effect transistors also can be used. Therefore, the distance between the pickup and associated display electronics or preamplifier must be short.Ĭapacitive sensors produce a sine wave by generating an RF signal that is amplitude-modulated by the movement of the rotor blades. It is not advisable to transport such a weak signal over long distances. At low flow rates, the output (the height of the voltage pulse) may be on the order of 20 mV peak-to-peak. The outputs of reluctance and inductive pick-up coils are continuous sine waves with the pulse train's frequency proportional to the flow rate. In some designs, only one blade is magnetic, and the pulse represents a complete revolution of the rotor. As each blade passes the coil, it generates a voltage pulse. In the inductance pick-up, the permanent magnet is embedded in the rotor, or the blades of the rotor are made of permanently magnetized material (Figure 1-B). The number of pulses per unit volume is called the meter's K-factor.įigure 1: Generation of Turbine Flow Signal Each pulse represents a discrete volume of liquid. As each blade passes the coil, a voltage is generated in the coil (Figure 1-A). In the reluctance pick-up, the coil is a permanent magnet and the turbine blades are made of a material attracted to magnets. Turbine rotation can be detected by solid state devices (reluctance, inductance, capacitive and Hall-effect pick-ups) or by mechanical sensors (gear or magnetic drives). The diameter of the rotor is very slightly less than the inside diameter of the metering chamber, and its speed of rotation is proportional to the volumetric flow rate. It consists of a multi-bladed rotor mounted at right angles to the fluid flow and suspended in the fluid stream on a free-running bearing. Invented by Reinhard Woltman in the 18th century, the turbine flow meter is reliable for use with both liquids and gases. Turbine flow meters are a type of velocity flow meter that have found widespread use in a variety of industrial applications – including aerospace, cryogenic, and custody transfer – for high accuracy measurements.
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