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An improved fluid flow meter for measuring a liquid flow rate is
disclosed. It comprises a container having an interior cavity, an
inlet opening, a vent opening, a first passageway and a second passageway.
The first passageway has an upper opening which is sealed by a pressure
transducer and has a lower opening which opens into the interior
cavity below the inlet and vent openings. A pressure signal produced
in the first passageway by liquid in the cavity is converted into
a flow rate by a processor which is connected to the pressure transducer.
The second passageway has a lower opening in communication with
the interior cavity above the lower opening of the first passageway
and an upper opening below the upper opening of the first passageway
which is connected to a downwardly depending drain tube to drain
the level of liquid in the cavity down by siphon action. In one
embodiment the vent opening and the second passageway are in communication
with the upper portion of a second cavity which is provided below
the first cavity and has a lower outlet opening.
A flow meter including a housing having inlet and outlet ports,
at least two associated pistons provided respectively in respective
cylinders in the housing, metering chambers defined respectively
on one sides of respective pistons, passages formed in the housing
for communicating the metering chambers with inlet and outlet ports,
and a valve mechanism provided in the housing and associated with
the movement of pistons for communicating either of the metering
chambers with the inlet port and communicating the other of metering
chambers with the outlet port. A check valve is provided in a passage
between the inlet port and the valve mechanism for permitting liquid
flow from the inlet port to the valve mechanism and preventing the
liquid flow in the reverse direction.
An instrumental error compensation circuit for a flow meter is
disclosed in which a flow rate calculated from an output signal
of the flow meter is identified with respect to a plurality of predetermined
sections of flow rates. Flow rate compensation coefficients are
calculated by linear interpolation on the basis of actually measured
data which are obtained in advance in accordance with instrumental
errors of the flow meter. Actual flow rates of a fluid are measured
with the instrumental errors of the flow meter compensated for by
the calculated coefficients.
An air flow meter circuit with a temperature compensation circuit
comprises an air flow rate detection circuit for generating an output
signal in accordance with an air flow rate, an output circuit for
amplifying the output signal of the air flow rate detection circuit
to produce an output signal whose value is so adjusted as to be
related to the value of the input signal in a predetermined relationship,
and a constant voltage circuit for supplying a predetermined reference
voltage to the air flow rate detection and output circuits. In order
to compensate the output of the air flow meter circuit for its changes
due to the influence of temperature coefficients of component parts
of both the air flow rate detection and output circuits, the temperature
coefficient of the output of the constant voltage circuit is so
adjusted as to cancel out the temperature coefficients of the parts
constituting the air flow meter circuit.
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