Page 229 - Instrumentation Reference Book 3E

Microprocessor-based and intelligent flowmeters 213
ards. The single flow path facilitates cleaning and
can be “pigged.” As with the D series, the range-
ability of the individual sensors is 20:1 and the
accuracy of measurement is +0.20% of rate f
sensor stability.
The DT series of sensors has been designed to
operate at up to 800 “F (426 “C). It is a dual tube
design using Hastelloy ‘2-12 tubing, 316L stain-
less steel manifolds and flanges. The sensor is
Figure 13.17 Coriolis effect. Courtesyof Fisher- enclosed in an hermetically sealed 304 stainless
Rosemount. steel case.
The model RTF9739 transmitter can be used in
conjunction with any of these sensors. The model
fluid and, for a particular sensor, the mass of the RFT9712 transmitter is designed to work with
tube is constant and the dimensions are known, the D3 DL, and DT series of sensors. Both trans-
so that the frequency of oscillation can be related mitters require an a.c. power supply (1 5 W max-
to the flu.id density. However, the modulus of imum) or a d.c. supply of 12-30V (14W
elasticity of the tube material varies with tem- maximum).
perature. and therefore a temperature sensor is The RFT9739 has two independently config-
included in the assembly so that a correction ured outputs, each of which can represent mass
can be applied to the density measurement for flow rate, density, or temperature. There is also
this effect. Thus the complete sensor assembly an isolated 0-15V frequency output which is
provides the signals from which the mass flow scalable from 1 to 10 000Hz and a control out-
rate, density: and temperature of the flowing fluid put which can represent flow direction or fault
can be determined by the associated transmitter. alarm. Digital communication can be implemented
There are four types of sensor: the CMF series, using the Bell 302 communication standard
the D series, the DL series, and the DT series. signal (see Section 13.10.4) superimposed on the
The “ELITE” (CMF) series of mass flowmeters 4-20mA circuit or via an RS 485 port. The
is characterized by improved accuracy (&0.15%f RFT9712 has similar features, except that it only
sensor stability), reduced pressure drop, and wide has one analog output which can be configured
rangeability (80: 1). The sensitivity to field effects to represent either mass flow rate, density, or
such as vibration and temperature has been temperature.
reduced. and for increased safety, the sensors Using the Rosemount model 268 hand-held
are enclosed in pressure containment housing terminal, the transmitter operational parameters
(see Table 13.5). which are set include:
The D series of sensors is available in a variety
of line sizes (Table 13.6) which enable mass flow (1) 4 and 2QmA points for the analog output(s)
rates from 0.1 1 b/mic to 25 000 lb/min to be mea- (2) Damping
sured. The rangeability of the individual sensors (3’) Selection of engineering units.
is 20:1 and the accuracy of measurement is The following informational data can be
3~0.20% of rate i sensor stability. There are alter- entered to allow identification and physical
native materials of construction for the wetted description of the transmitter:
parts and the sensor itself is enclosed in an her-
metically sealed case. (1) Tag (eight alphanumeric characters)
The DL series sensors (Table 13.7) are con- (2) Descriptor (1 5 alphanumeric characters)
structed with a continuous stainless steel flow (3) Message (32 alphanumeric characters)
tube, and the design meets the 3A Sanitary Stand- (4) Date.

Table13.5 Outline details of the ELITE (CMF) series of mass flow sensors
i\ilodel rode Nomirial Usable rmge Zero stability Pressure rating Ten7j~ei.ntin.e
flow range (lb/min) (lblmin) (psi) rut iiig
(lblmin) (OF)
CMF025 040 0-80 0.002 1450 -400 to +400
CMF050 0-125 0-250 0.006 1450 -400 to +400
CMFlOO 0-500 0-1000 0.025 1450 -400 to +400
CMF2OO 0-1 600 0-3200 0.08 1450 -400 to +400
CMF300 0-5000 0-10000 0.25 1450 -400 to +400