tect the flow sensor from the effects of the surrounding environment (dirt, condensation, and mechanical interference), which could interfere with operation. If the vibrating tube(s) of the Coriolis meter were to fail, the housing containing the tube(s) would be exposed to the process fluid and conditions, which could possibly cause housing failure. It is important to take into consideration the following possibilities:
(1) the pressure within the housing might exceed the design limits
(2) the fluid might be toxic, corrosive, or volatile and might leak from the housing
(b) In order to avoid such problems, certain housing designs provide
(1) secondary pressure containment
(2) burst discs or pressure-relief valves, fluid drains or vents, etc.
For guidelines on specifying secondary pressure containment, see Appendix B.
3.6.7 Cleaning. For general guidelines see para. 3.3.7. Care should be taken to ensure that cleaning conditions (fluids, temperatures, flow rates, etc.) have been selected to be compatible with the materials of the Conohs meter.
3.7 Transmitter (Secondary Device)
Coriolis meters are multivariable instruments providing a wide range of measurement data from a single connection to the process. The electronics are typically located in an enclosure, which may be mounted locally on the sensor, or remotely, and connected to the sensor using a cable. When selecting the most appropriate transmitter arrangement and options, consideration should be given to the following:
(a) the electrical, electronic, climatic, and safety compatibility
(b) the hazardous area classification of the flow sensor, and transmitter, and the availability of special enclosure options
(c) the transmitter enclosure mounting (i.e., integral or remote)
(d) the number and type of outputs, including digital communications
(e) the ease and security of programming
(f the meter diagnostic capability, and whether there are output(s) to allow remote indication of system errors
‘g) the available input options (e.g., remote zero adjustment, totalizer resetting, alarm acknowledgment)
(ii) the capability for local display and operation
(a) As Coriolis meters are an integral part of the piping (in-line instrumentation), it is essential that the instrument be subjected to testing procedures similar to those applied to other in-line equipment.
In addition to the instrument calibration and/or performance checks, the following optional tests may be performed to satisfy the mechanical requirements:
(1) dimensional check
(2) optional hydrostatic test, in accordance with a traceable procedure as specified by the user
(3) radiographic and/or ultrasonic examination of the primary device to detect internal defects (i.e., inclusions) and verify weld integrity
Results of the above tests should be presented in a certified report, when requested.
(b) In addition to the above reports, the following certificates, when requested, should be available:
(1) material certificates, for all pressure-containing parts
(2) certificate of conformance (electrical area classifica tions)
(3) certificate of suitability for legal trade or custody transfer
(4) calibration certificate and performance results
(5) certificate of suitability for sanitary applications
Coriolis meters directly measure mass flow rate, and some can measure the flowing density of the process fluid. Paragraphs 5 and 6 describe the underlying principles for these measurements. Inferred measurements such as volumetric flow and concentration are described in paras. 7 and 8.
5.1 Apparatus
5.1.1 Principle of Operation. Coriolis meters operate on the principle that inertial forces are generated whenever a particle in a rotating body moves relative to the body in a direction toward or away from the center of rotation. This principle is shown in Fig. 1.
A particle of mass ni slides with constant velocity, v, in a tube, T, that is rotating with angular velocity, w, about a fixed point, P. The particle undergoes an acceleration, which can be divided into two components:
(a) a radial acceleration, a,. (centripetal), equal to w2r and directed towards P
(b) a transverse acceleration, a1 (Coriolis), equal to 2w Xv (vector cross product) at right angles to a,. and in the direction shown in Fig. 1
To impart the Coriolis acceleration, a1, to the particle, a force of magnitude 2vwin is required in the direction of a. This force comes from the tube. The reaction of this force back on the tube is commonly referred to as the Coriolis force.