Abstrict A temperature compensator for a liquid flow meter. A bellows unit
is mounted in the conduit carrying the liquid measured and an output
from the bellows unit is taken to a disc-and-wheel mechanical compensator
by means of a flexible cable drive. An adjustable pivot lever coupling
allows adjustment of the drive ratio to the compensator according
to the nature of the liquid.
Claims We claim:
1. A temperature responsive fluid flow meter for determining the
rate of fluid flow through a conduit, said meter comprising:
input shaft means to be positioned in the fluid conduit for rotating
in response to the flow of fluid through the conduit;
flow rate indicator means for indicating the rate of fluid flow
in the conduit;
differential means connected between said input shaft means and
said indicator means for driving said indicator means in response
to the rotation of said input shaft means;
adjustable calibration control means connected to said differential
means for adjusting the drive ratio of said differential means;
and
temperature control means connected to said calibration means to
be operatively positioned in the flow of fluid being metered for
regulating said calibration means in correlation with the temperature
of the fluid, said temperature control means being comprised of:
capsule means substantially affording the entire temperature responsive
sensing for the regulating input to said calibration control means,
and adapted for immersion in the flowing fluid, said capsule means
comprising a fluid tight enclosure with respect to the flowing fluid
and containing a bellows unit surrounded by an enclosed volume of
fluid fill for said bellows unit to contract and expand in accordance
with changes in the temperature of the metered fluid conducted through
said capsule means enclosure and fluid fill therein, and
a flexible cable connecting said capsule means and said calibration
control means, said flexible cable having
a flexible outer sleeve operatively anchored at one end to said
capsule means, and
a flexible inner cable through said outer sleeve operatively connecting
at one end to said bellows unit and at the other end to said calibration
control means;
said calibration control means being comprised of:
a disc on the end of said input shaft means,
a rotatable wheel radially contacting said disc, and
a rotatable shaft supporting said wheel and operatively connected
to said flexible inner cable of said temperature control means and
to said differential means; and
said differential means being comprised of:
an output shaft means connected to said indicator means for operating
said indicator means,
first and second gears operatively connected to said output shaft
and rotatable therewith;
first gear means on said input shaft means for transferring the
motion of said input shaft to said first gear, and
second gear means on said rotatable shaft supporting said wheel
for transferring the rotational motion of said shaft to said second
gear.
2. A meter as claimed in claim 1 wherein the motion of said second
gear means is subtracted from the motion of said first gear means.
Description The invention relates to a liquid flow meter and particularly to
a temperature compensation device for use in association with such
a flow meter.
BACKGROUND OF THE INVENTION
Liquid flow meters have application in many fields for measuring
the flow of liquid through conduits. The true mass flow of liquid
through a conduit depends upon the temperature of the liquid, since
the liquid expands with temperature. The temperature of the liquid
may vary because of changes in ambient temperature or because of
artificial heating to improve efficiency of pumping in the case
of liquids which have high viscosity at low temperatures. Accordingly,
there is a requirement to provide compensation in the output of
a flow meter in accordance with the temperature of the liquid.
A temperature-dependent mechanical output has been achieved hitherto
by the use of a fluid-filled capsule immersed in the liquid of which
the flow is being measured. The capsule is coupled to a remote bellows
unit by capillary tubing and the variation of expansion of the fluid
by virtue of the temperature of the liquid changes the pressure
on the bellows and thus effects a mechanical movement. However,
ambient temperature changes at the bellows unit and the capillary
tubing also produce mechanical movement which would give rise to
an error. Compensation for such ambient temperature changes of the
bellows unit and capillary tubing has been effected by providing
a second sealed bellows arrangement in tandem with the first and
assembled in such a way that changes in ambient temperature are
compensated for. Such a prior arrangement is convenient in that
the small diameter capillary tubing makes it possible to mount the
capsule in a convenient position and allows easy coupling to a flow
indicator compensation arrangement. However, the provision of a
second bellows arrangement for the correction of ambient temperature
effects is unduly complex. The present invention seeks to provide
an improved temperature compensating arrangement.
SUMMARY OF THE INVENTION
According to the invention there is provided a liquid flow meter
having a drive adapted to be driven by a liquid, the flow rate of
which is to be measured; a flow indicator output; a calibration
control coupled between the drive and the indicator output; an input
of the calibration control which is adjustable to vary the drive
ratio between the drive and the indicator output; a temperature
control capsule for immersion in the flowing liquid, the capsule
including a bellows unit which contracts and extends in accordance
with the temperature of the liquid; and a flexible cable comprising
an outer sleeve anchored at one end to the capsule and at the other
end to the calibration control and an inner cable coupled at one
end to the bellows unit and at the other end to the input of the
calibration control. It will be seen that with this arrangement
the bellows unit is not remote from the capsule and is immersed
in the liquid. There is, therefore, no need to compensate for ambient
temperature changes at the bellows unit. Instead of providing a
pressure output in a capillary tube, the present invention provides
a direct mechanical output via a flexible cable which has the same
virtue of easy fitting as does a capillary tube.
Different liquids have different temperature coefficients of expansion
and a preferred feature of the present invention provides means
coupling the flexible cable to the input of the calibration control,
which coupling means is effective to adjust the ratio between linear
movement of the inner cable of the flexible cable and corresponding
linear movement of the input to the calibration control. Preferably,
the adjustable coupling comprises a lever to which the inner cable
of the cable and the input to the calibration control are coupled
at opposite ends and a pivot which is slidable along the lever.
The position of the pivot will adjust the effect of the cable movement
on the input to the calibration control. The position of the slidable
pivot can be set in accordance with the nature of the liquid flowing.
In a preferred embodiment of the present invention the calibration
control comprises a disc and wheel arrangement, the wheel being
driven frictionally by the disc at a rate dependent upon the position
of the wheel on the disc. A differential unit receives one input
from the wheel and another input from the output of the flow meter.
The output from the flow meter also drives the disc. The output
from the differential drives the indicator. The arrangement is such
that the output from the flow meter is applied through the differential
to the indicator and a small proportion is subtracted in the differential,
the proportion being determined by the position of the wheel on
the disc. The wheel position is determined by the drive applied
through the flexible cable.
BRIEF DESCRIPTION OF THE INVENTION
The invention will further be described with reference to the accompanying
drawings, of which:
FIG. 1 is a cross-sectional view of the temperature compensation
capsule of a flow meter in accordance with the invention;
FIG. 2 is a cross-sectional view of the input coupling to the calibration
control of the flow meter embodying the capsule of FIG. 1;
FIG. 3 is a section taken at K--K of FIG. 2; and
FIG. 4 is a cross-sectional view of the calibration control of
the flow meter.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1 there is shown in cross-section part of the
wall of a conduit C which carries a liquid, the flow of which is
to be measured. The wall of the conduit is drilled so that liquid
flowing in the conduit enters a bore 3. The bore is blocked by a
temperature compensation unit U which is threaded into the wall
of the conduit and sealed by an O-ring R. The unit U has a capsule
1 which is clear of the wall of the bore 3 and is therefore immersed
in the flowing liquid. The capsule 1 contains an operating fluid
which exerts pressure on the end 4 of an operating rod 5. The rod
is sealed to the wall of the capsule by a bellows unit 2 and is
urged downwardly (as seen in the Figure) by a coil spring 6. As
the temperature of the operating fluid in the capsule increases,
the pressure on the end 4 of the rod 5 increases and the rod is
moved against the action of spring 6. The position of the rod 5
depends upon the temperature of the flowing liquid.
The end 4 of the rod 5 is coupled to an inner cable 7 of a flexible
cable which has a flexible outer sleeve 8. This sleeve 8 is fixed
to the body 9 of the unit U.
Referring now to FIG. 2 there is shown the connection for the
other end of the flexible cable. The flow meter has a vane arrangement
(not shown) which is driven by the flowing fluid to rotate an output
shaft in accordance with the flow of the fluid. The output shaft
is coupled to drive an indicator output, and between the drive and
the indicator output is an adjustable calibration control. The control
comprises a disc 30 driven by an input shaft 25 (FIG. 4) which is
turned by the drive from the vane arrangement. The disc drives a
wheel 31 which makes frictional contact with one face 30a of the
disc 30 and which is movable radially over the disc face. The radial
movement of the wheel is controlled by movement of a sleeve 15 which
is fixed to the wheel and which is threaded on a rod 13. Rod 13
is coupled to one end of a lever 11. The other end of the lever
11 is coupled to the inner cable 7 of the flexible coupling (FIG.
1). The outer sleeve 8 of the flexible coupling is fixed to a casing
20 which houses the lever 11 and which is fixed to the casing of
the calibration control. The lever 11 pivots about a pivot 12 and
it will be seen that the linear movement of the inner cable 7 produces
a corresponding linear movement of the rod 13 and thus of the wheel
31.
Because of the different temperature co-efficients of expansion
of different liquids, the amount of movement of wheel 31 necessary
for a given temperature rise will be different for different liquids.
In order to allow for this, the pivot 12 is movable along the lever
11. FIG. 3 shows a section taken at K--K of FIG. 2 and illustrates
the manner in which the pivot is movable. It will be seen that the
pivot 12 is mounted on a stub 21 which is threaded on a threaded
rod 22. Movement of the stub 21 and thus the sleeve which constitutes
pivot 12 along the rod 22 is effected by turning the rod 22 by means
of a screwdriver in a screwdriver slot 24. Thus, the compensation
co-efficient for a given liquid can be set by manipulation of the
pivot position for the lever 11.
As further shown in FIG. 4 the shaft 25 drives bevel gears 26
and 27 and the gear 27 is coupled to drive an input sun gear 28
of a differential 29. The disc 30 is fixed to gear 26 and drives
the wheel 31. Wheel 31 drives a gear 33 which is coupled to the
cage gear 34 of the differential 29. The wheel 34 carries the planet
gears 35 and assists in driving on output sun gear 36 of the differential.
This gives a final drive via a shaft 37. The shaft 37 is coupled
to drive the fluid flow indicator (not shown) directly.
The basic drive for the output from the meter is thus given by
shaft 25 through the differential to shaft 37. However, an adjustable
decrement is subtracted from this drive by means of the friction
wheel 31 and the differential 29. The component subtracted is adjustable
by linear movement of the wheel 31 under control of the shaft 13
as described. It is to be noted that the contribution of the friction
wheel is subtracted rather than added to the drive and this has
the advantage of allowing a greater torque load to be transmitted
by the calibrating mechanism, since the torque reaction created
by the counter and accessories being driven by the calibrator tends
to assist rather than oppose the operation of the wheel and disc
mechanism. |