TM No. 377 



the axes of two cylinders. If the cylinder axes are aligned coincident with 

 the X and Z axes, the associated velocity components may be written simply 

 as u and w« respectively. 



Each flow meter consists of a brass right circular cylinder 21..5 cm long 

 with a 13.3 cm inside diameter and a 0.3 cm wall thickness. The cylinders 

 are held together by two supporting Unbolts which are made of 3/8-inch brass 

 rod and clamped to a T-shaped piece welded to the support pipe. The flow 

 sensor is a five bladed impeller mounted within the cylinder at its mid-point 

 so that the axis of rotation is coincident with that of the cylinder. The 

 impeller shaft consists of a Teflon cylinder with brass needle bearing 

 inserts at each end. The fore and aft impeller bearing supports are 

 suspended at each end by three thin struts. The needle bearings can be 

 adjusted in or out to provide proper seating of the pins in the axis support 

 housing held by the supporting struts. 



The impeller blades are made of 1.5 mm thick micarta (phenol formaldehyde 

 with a cellulose filler) 3 which has a specific gravity of about 1.3. The 

 blades are fixed to the Teflon shaft at an angle of about 45° with respect 

 to their axis of rotation. At the outer tip of each impeller blade is 

 mounted a small iron slug weighing about 1 gm and having dimensions of about 

 10 by 4 by 0.5 mm. The slugs are set into the blade tips with epoxy glue. 

 The long axis is normal to the impeller axis and is positioned so that the 

 end of the slug is flush with the outer tip of the blade. 



The impeller responds to the component of flow parallel to the cylinder 

 axis by spinning s thus allowing flow thro?jgh the cylinder. The angular 

 velocity of the impeller is a known function of the magnitude of the flow. 

 The rotation of the impeller as a function of tine is monitored by a 

 magneto- inductive coupling between the iron slugs and an energized miniature 

 induction coil. This coil and the associated circuitry are contained within 

 the small brass pillbox braised to the side of the cylinder (see figure II-3)„ 



Figure II-4 is an electrical schematic of the circuitry. The arm of 

 the induction coil L^ is excited by a 2 kc carrier oscillator circuit as 

 shown. As the impeller spins,, the iron slugs pass within 0.5 = 1.0 mm of 

 the coil arms. This causes a change in the inductance and s hence s a 

 perturbation of the 2 kc carrier frequency. This magnetic induction is also 

 registered in coil windings Lo and L3 which are mounted on either side of 

 the winding Li. The sense of impeller rotation determines which winding 

 (L2 or L3) is perturbed first. By means of the parallel diode circuits s the 

 shape of the amplitude modulated voltage disturbance entering the transistor 

 NPN 2N385 is uniquely defined by the sequence of coil excitation. This 

 pulse is amplified through PNP 2N525 and led to the surface recorder. The 

 entire circuitry 3 consisting of a miniature coil s oscillator;, and modulator= 

 amplifier,, is potted within the pillbox. The surface electronics include 

 the DC power supply,, a high and low amplification circuit,, and the zero 

 balance. The input voltage from the DC power supply and the output signal 

 are led to the pillbox by two watertight male connectors manufactured by 



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