IM-P198-05 MI Issue 2 9
2.4 How the RIM20 rotor insertion flowmeter operates
The RIM20 rotor insertion flowmeters are designed to monitor mass flowrate by directly
measuring three variables-fluid velocity, temperature and pressure. The built-in flow
computer calculates the mass flowrate and volumetric flowrate based on these three direct
measurements. To measure fluid velocity, the flowmeter incorporates a rotating turbine in
the flow stream. The rotation is converted into an electrical output which is proportional to
fluid velocity.
Temperature is measured using a platinum resistance temperature detector (PRTD) and
pressure measurement is achieved using a solid-state pressure transducer.
2.5 Velocity measurement
Fluid passing through the turbine causes its rotor to spin. The rotor is fabricated from 17-4PH
stainless steel which is slightly magnetic, and is positioned in close proximity to a passive
magnetic pickup coil. As each blade rotates by the pickup coil, a small sinusoidal voltage is
generated. This sinusoidal voltage is then amplified, filtered, and shaped by the measurement
electronics. The frequency of the signal is proportional to the flowing velocity.
2.6 Flow velocity range
To ensure trouble-free operation, turbine flowmeters must be correctly sized so that the flow
velocity range through the meter lies within the measurable velocity range. The measurable
range is defined by the minimum and maximum velocity using the following table.
Rotor
Gas or Steam
Minimum velocity Maximum velocity
m/sec ft/sec m/sec ft/sec
R40 1.07 3.5 13.11 43.0
R30 1.22 4.0 19.05 62.5
R25 1.52 5.0 24.38 80.0
R20 2.13 7.0 30.48 100.0
R15 2.59 8.5 41.03 134.6
R10 3.66 12.0 62.48 205.0
Table 1 Measurable range
The pressure drop for the RIM20 rotor insertion flowmeters is negligible.
2.7 Temperature measurement
RIM20 rotor insertion flowmeters use a 1000 ohm platinum resistance temperature detector
(PRTD) to measure fluid temperature.
To Next Page
Loading...
