ME360 Spring 2014

Problem Handout #11
Drag Force Flow Meter

R. Larson

A drag force flow meter is created in order to measure flow velocity in a large 48" diameter flume pipe that carries water from a diversion dam to a power station: The system uses a .375" wide X .750" thick rectangular steel rod, 24" long, mounted in cantilever fashion to the pipe wall to support a circular drag disk. The 4.00 " diameter drag disk is completely submerged in the flow.

Two strain gages are mounted to the rod at a location 12 inches from the center of the disk, and are wired into a bridge circuit as shown. Find the output voltage of the system.

  

NOTE: The following calculation is not correct, as it assumed R2 and R4 were swapped! However, it does demonstrate the techniques applicable.
(Will fix and update if I have time!)