Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Frequency of cyclic current or voltage
Reexamination Certificate
2000-11-06
2002-09-24
Le, N. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Frequency of cyclic current or voltage
C324S120000, C073S861355, C702S045000
Reexamination Certificate
active
06456057
ABSTRACT:
FIELD OF INVENTION
This invention relates to a Coriolis flowmeter that has a booster amplifier for increasing the power of the drive signals transmitted from a flowmeter electronics to a flowmeter sensor. More particularly, this invention relates to a booster amplifier which is operable with flowmeter sensors having flow tubes of straight and curved geometries, on numerous electrical voltage standards and under various environmental conditions.
PROBLEM
It is known to use Coriolis mass flowmeters to measure mass flow and other information with respect to materials flowing through a pipeline as disclosed in U.S. Pat. No. 4,491,025 issued to J. E. Smith, et al., of Jan. 1, 1985 and Re. 31,450 to J. E. Smith of Feb. 11, 1982. These flowmeters typically comprise a flowmeter electronics portion and a flowmeter sensor portion. Flowmeter sensors have one or more flow tubes of a straight or curved configuration. Each flow tube configuration has a set of natural vibration modes, which may be of a simple bending, torsional, radial or coupled type. Each flow tube is driven to oscillate at resonance in one of these natural modes. The natural vibration modes of the vibrating, material filled systems are defined in part by the combined mass of the flow tubes and the material within the flow tubes. Material flows into the flowmeter sensor from a connected pipeline on the inlet side of the flowmeter sensor. The material is then directed through the flow tubes and exits the flowmeter sensor to a pipeline connected on the outlet side of the flowmeter sensor.
Flowmeter sensors typically include a driver for applying vibrational force to the flow tubes. The driver receives a drive signal from the flowmeter electronics and induces resonant vibration of the flow tubes. The frequency of the drive signals for a flowmeter sensor having a flow tube of a straight configuration can differ significantly from those of a flowmeter sensor having flow tubes of a curved configuration.
When there is no material flowing through a flowmeter sensor, all points along the flow tubes oscillate with a substantially identical phase. As material flows through the flow tubes, Coriolis accelerations cause points along the flow tubes to have a different phase. The phase on the inlet side of the flowmeter sensor lags the driver, while the phase on the outlet side of the flowmeter sensor leads the driver.
Flowmeter sensors typically include two pick-offs for producing sinusoidal signals representative of the motion of the flow tubes at different points along the flow tubes. A phase difference of the sinusoidal signals received from the pick-offs is calculated by the flowmeter electronics. The phase difference between the pick-off signals is proportional to the mass flow rate of the material flowing through the flowmeter sensor.
One of the pick-off signals is also used to form a drive signal control loop. The natural vibration modes of the vibrating, material filled system is defined in part by the combined mass of the flow tubes and the material within the flow tubes. Changes in the tube wall thickness, tube vibrational stiffness or mass of the material within the flow tube may require modified drive signals to induce resonant vibration. A drive control loop allows the flowmeter electronics to continuously generate drive signals that induce resonant vibration of the flow tubes.
Flowmeter sensors are typically sized according to a range of material flow rates appropriate for the flowmeter sensor. In order to increase the material flow rate, larger flow tubes may be utilized. Increases in flow tube size may increase certain flow tube parameters such as tube wall thickness and vibrational stiffness. The drive signal received from the flowmeter electronics may require additional power in order for the driver to induce resonant vibration of the larger flow tubes. A booster amplifier can be used to increase the power of the drive signals received from the flowmeter electronics.
A flowmeter sensor and a flowmeter electronics are typically interconnected by nine leads along a single path. Where the flowmeter electronics is remotely mounted from the flowmeter sensor, a 9-wire cable may be used. Where the flowmeter electronics is integrally mounted to the flowmeter sensor, a 9-pin feed-through may be used. Of the nine leads, two connect the flowmeter electronics to the driver, two connect the flowmeter electronics to one pick-off, two connect the flowmeter electronics to another pick-off, and three connect the flowmeter electronics to the temperature sensor. A booster amplifier is typically inserted along the single path interconnecting the flowmeter electronics and the flowmeter sensor.
It is a problem to design a booster amplifier that can operate on multiple AC voltage standards. Coriolis flowmeters are used worldwide. Individual countries and regions have standardized on certain electrical voltage levels. For example, the 115 volt AC standard is common throughout the United States, the 100 volt AC standard is common throughout Japan, and the 230 volt AC standard is common throughout Europe.
A traditional approach to designing booster amplifiers for Coriolis flowmeters has been to create separate booster amplifier models for each voltage standard. However as the matrix of booster amplifiers grows, the number of parts which must be specified, purchased and inventoried increases, manufacturing and labor costs increase through process complexity, and finished product inventories increase.
A further problem is designing a booster amplifier that is capable of amplifying drive signals for straight and curved flow tube geometries. The drive signals for a flowmeter sensor having flow tubes of a curved configuration can require a drive frequency approximating 40 Hz. The drive signal for a flowmeter sensor having a flow tube of a straight configuration can require a drive frequency approximating 800 Hz. As the frequency of the resonant vibration of the flow tubes increases, inaccuracies in the drive system become magnified resulting in mass flow measurement error.
A traditional approach to designing booster amplifiers for flow tubes requiring higher frequency drive signals has been to increase the power of the drive signal. However, power sources providing standard AC voltage may not enable sufficient power to be imparted to the drive signal. Examples of standard AC voltages are the 115 volt AC standard common throughout the United States, the 100 volt AC standard common throughout Japan, and the 230 volt AC standard common throughout Europe.
A further problem is designing a booster amplifier that meets regulatory agency safety standards for explosive environments. Coriolis flowmeters are used in various environments, ranging from inert to explosive. As the operating environment for the flowmeter becomes more severe, increasingly stringent requirements must be met by the flowmeter. Individual countries and regions have standardized flowmeter safety requirements through regulatory agencies. For example, UL determines flowmeter safety requirements in the United States, CENELEC determines flowmeter safety requirements in Europe, CSA determines flowmeter safety requirements in Canada and TIIS determines flowmeter safety requirements in Japan. A booster amplifier designed to meet an agency's safety requirements for an explosive environment will typically meet that agency's requirements for less severe environments. However, a booster amplifier meeting an agency's safety requirements for an explosive environment may not meet another agency's standards for an explosive environment. For purposes of this discussion, an explosive environment is an environment that includes a volatile material which can be ignited if a spark, excessive heat, or excessive energy is introduced to the environment.
One approach to meeting flowmeter safety requirements for an explosive environment is to encase the booster amplifier in an explosion proof housing. Methods used to achieve an explosion proof housing include encapsulation, pressurization and
McCormick Kurtis Leroy
Weber William Randolph
Zolock Michael John
Deb Anjan K.
Faegre & Benson LLP
Le N.
Micro Motion Inc.
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