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In Emerson’s turbine flowmeters, the turbine rotor is mounted on an axis between two sets of flow straighteners. The fluid flows through the flow meter, causing the turbine blades to rotate. In gear-type flowmeters, the sensor is mounted on the turbine, and pulses are generated each time a blade passes beneath it. The frequency of the sensor is proportional to the flow rate within the range of limitation. For example, turbine flowmeters generally do not require linearization. A precision of full scale +/- 1% can be achieved. When used with a linearized lookup table, this 1\" turbine flowmeter can also be used over a wider range, with an accuracy of 1% of the indicated reading. A gain ratio of 30:1 is quite common. Using a turbine instead of gears means that the flow meter requires less energy to operate and has a lower pressure drop; for example, at a flow rate of 400 L/min or less, the pressure drop is 3 bar (44 psi), depending on the inner diameter size. The disadvantage of this type of flowmeter is its susceptibility to changes in viscosity. Therefore, it is commonly used for fluids with a viscosity below 100 cSt. The Emerson elliptical gear flowmeter is similar to traditional flowmeters, but it uses two elliptical gears that rotate 90° relative to each other inside the housing. The fluid flows through the cavity around the gears, and the rotation frequency is directly related to the volume of fluid passing through the flow meter. Since non-intrusive flowmeters (such as ultrasonic flowmeters) do not need to \"penetrate inside the system\" and do not cause pressure drops, hydraulic pipes are usually small in size, even less than 25 millimeters (1 inch), which results in short transmission times. Properly installing the transmitter and receiver components of a flow meter is very time-consuming, especially when the flow meter is portable.