Gate-Type Meters
About measuring with gate-type meters
The gate meter was the earliest device in
this class. It consists of a spring-loaded, hinged flap mounted at right
angles to the direction of fluid flow in the fluid-carrying pipe. The
flap is connected to a pointer outside the pipe. The fluid flow deflects
the flap and pointer and the flow rate is indicated by a graduated scale
behind the pointer. The major difficulty with such devices is in
preventing leaks at the hinge point.
A variation on this principle is the air-vane meter which measures
deflection of the flap by a potentiometer inside the pipe. This is
commonly used to measure air flow within automotive fuel-injection
systems.
Another device in this class is the target meter. This consists of a
circular disk-shaped flap in the pipe. Fluid flow rate is inferred from
the force exerted on the disk measured by strain gauges bonded to it.
This meter is very useful for measuring the flow of dilute slurries but
it does not find wide application elsewhere as it has a relatively high
cost.

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