Drive circuit modal filter for a vibrating tube flowmeter

DETAILED DESCRIPTION Coriolis Flowmeter in General--FIG.
1 FIG.
1 shows a Coriolis flowmeter 5 comprising a Coriolis meter assembly 10 and meter electronics 20.
Meter electronics 20 is connected to meter assembly 10 via leads 100 to provide density, mass flow rate, volume flow rate and totalized mass flow information over path 26.
A Coriolis flowmeter structure is described although it is apparent to those skilled in the art that the present invention could be practiced in conjunction with a vibrating tube densitometer without the additional measurement capability provided by a Coriolis mass flowmeter.
Meter assembly 10 includes a pair of flanges 101 and 101', manifold 102 and flow tubes 103A and 103B.
Connected to flow tubes 103A and 103B are driver 104 and pick-off sensors 105 and 105'.
Brace bars 106 and 106' serve to define the axis W and W' about which each flow tube oscillates.
When flowmeter 10 is inserted into a pipeline system (not shown) which carries the process material that is being measured, material enters meter assembly 10 through flange 101, passes through manifold 102 where the material is directed to enter flow tubes 103A and 103B, flows through flow tubes 103A and 103B and back into manifold 102 from where it exits meter assembly 10 through flange 101'.
Flow tubes 103A and 103B are selected and appropriately mounted to the manifold 102 so as to have substantially the same mass distribution, moments of inertia and elastic modules about bending axes W--W and W'--W', respectively.
The flow tubes extend outwardly from the manifold in an essentially parallel fashion.
Flow tubes 103A-103B are driven by driver 104 in opposite directions about their respective bending axes W and W' and at what is termed the first out of phase bending mode of the flowmeter.
Driver 104 may comprise any one of many well known arrangements, such as a magnet mounted to flow tube 103A and an opposing coil mounted to flow tube 103B and through which an alternating current is passed for vibrating both flow tubes