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A mass flow measurement and control device includes an enclosure with a Coriolis mass flowmeter situated therein. The Coriolis mass flowmeter has a flow-tube made of a high-purity plastic material, a driver coupled to the flow tube for vibrating the flow tube, and a pickoff coupled to the flow tube

A mass flow measurement and control device includes an enclosure with a Coriolis mass flowmeter situated therein. The Coriolis mass flowmeter has a flow-tube made of a high-purity plastic material, a driver coupled to the flow tube for vibrating the flow tube, and a pickoff coupled to the flow tube for sensing Coriolis deflections of the vibrating flow tube. A pinch valve includes an elastomeric tube made of a high-purity plastic material in fluid communication with the flow tube. An actuator with a ram operatively connected thereto is situated adjacent the elastomeric tube, and a reference surface is positioned generally opposite the ram such that the elastomeric tube is squeezable between the ram and the reference surface. A controller may also be provided, which receives an output signal from the Coriolis flowmeter and provides a control output signal to the pinch valve actuator in response to the flowmeter output signal and a setpoint signal.

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A mass flow measurement and control device includes an enclosure with a Coriolis mass flowmeter situated therein. The Coriolis mass flowmeter has a flow-tube made of a high-purity plastic material, a driver coupled to the flow tube for vibrating the flow tube, and a pickoff coupled to the flow tube

A mass flow measurement and control device includes an enclosure with a Coriolis mass flowmeter situated therein. The Coriolis mass flowmeter has a flow-tube made of a high-purity plastic material, a driver coupled to the flow tube for vibrating the flow tube, and a pickoff coupled to the flow tube for sensing Coriolis deflections of the vibrating flow tube. A pinch valve includes an elastomeric tube made of a high-purity plastic material in fluid communication with the flow tube. An actuator with a ram operatively connected thereto is situated adjacent the elastomeric tube, and a reference surface is positioned generally opposite the ram such that the elastomeric tube is squeezable between the ram and the reference surface. A controller may also be provided, which receives an output signal from the Coriolis flowmeter and provides a control output signal to the pinch valve actuator in response to the flowmeter output signal and a setpoint signal. d therebetween. 2. The multi-phase flat-type PM stepping motor according to claim 1, wherein said coils arranged on said first stator unit are deviated from said coils arranged on said second stator unit by 1/2 of the coil arrangement angular pitch, and said permanent magnets arranged on said first rotor unit are deviated from said permanent magnets arranged on said second rotor unit by 1/4 of the angular pitch of the magnetic poles having the same polarity. 3. The multi-phase flat-type PM stepping motor according to claim 1, wherein the total number Pr of said N-poles and S-poles of each rotor unit satisfies the following equation: Pr=m±2 where m is a phase number. 4. The multi-phase flat-type PM stepping motor according to claim 1, wherein each of said first and second stator units has six air-core coils to form a 6-phase motor. 5. The multi-phase flat-type PM stepping motor according to claim 1, wherein each of said first and second stator units has ten air-core coils to form a 10-phase motor. 6. A driving circuit for the multi-phase flat-type PM stepping motor according to one of claims 1 through 5, wherein the respective opposite air-core coils are serially connected to form a plurality of coil groups, and terminals at one side of said coil groups are connected to each other for each of said first and second stator units to permit plural phase excitation. 7. The driving circuit according to claim 6, wherein the connection point of said coil groups arranged on said first stator unit is connected to the connection point of said coil groups arranged on said second stator unit. 8. The driving circuit according to claim 6, wherein terminals at the side opposite to the connection point of said coil groups are connected to connection points of serially connected switching elements, respectively. 9. A multi-phase flat-type PM stepping motor, comprising: a first motor unit that comprises: a first stator unit providing a plurality of magnetic poles that are radially arranged on a first isolating magnetic disc, each of said magnetic poles having pole teeth on the top thereof and being wound by a coil; and a first rotor unit having a plurality of permanent magnets that are alternatively magnetized in N-pole and S-pole and radially arranged on a second magnetic disc at the pitch corresponding to the pitch of said pole teeth with a predetermined air gap with respect to the magnetic pole surface of said first stator unit; and a second motor unit that comprises: a second stator unit providing a plurality of magnetic poles that are radially arranged on a third isolating magnetic disc, each of said magnetic poles having pole teeth on the top thereof and being wound by a coil; and a second rotor unit having a plurality of permanent magnets that are alternatively magnetized in N-pole and S-pole and radially arranged on a fourth magnetic disc at the pitch corresponding to the pitch of said pole teeth with a predetermined air gap with respect to the magnetic pole surface of said second stator unit, wherein said first and second motor units are coaxial and symmetric with each other about a non-magnetic disc arranged therebetween. 10. The multi-phase flat-type PM stepping motor according to claim 9, wherein each of said pole teeth is a projection whose sectional shape is rectangular, a predetermined number of said pole teeth are radially formed on each of said magnetic poles at a predetermined pitch. 11. The multi-phase flat-type PM stepping motor according to claim 9, wherein said coils arranged on said first stator unit are deviated from said coils arranged on said second stator unit by 1/2 of the coil arrangement angular pitch, and said permanent magnets arranged on said first rotor unit are deviated from said permanent magnets arranged on said second rotor unit by 1/4 of the angular pitch of the magnetic poles having the same polarity. 12. The multi-phase flat-type PM stepping motor according to claim 9, wherein the to