Abstrict A temperature compensator for a fluid flow meter, e.g. an industrial
gas meter, has a temperature sensing element which contacts the
flow of fluid being metered. The temperature sensing element adjusts
the position of a cam surface so as to limit the arc of travel of
an oscillating cam striker element in accordance with the temperature
of the fluid. The cam striker element is driven in both directions
by means operatively associated with a driving element driven by
the fluid flow. A recorder records the distance travelled by the
cam striker element in a given time, so as to provide a reading
of temperature compensated fluid flow.
Claims I claim the following to be my invention:
1. A temperature compensating device for use with a fluid flow
meter, said device comprising:
a driving element adapted to be driven by fluid flowing through
the meter;
first fluid volume recording means drivingly connected with said
driving element to record fluid volumes flowing through the meter;
temperature sensing means adapted to contact the fluid flowing
through the meter;
a cam surface bearing element connected to said temperature sensing
means, the position of said cam surface being determined by the
temperature sensed by the temperature sensing means;
an oscillatable cam striker element adapted to oscillate through
an arc of travel defined at the first extremity by contact with
said cam surface and at the second extremity by pre-set limiting
means;
driven means which drives the cam striker element for oscillation
in both directions, into and out of contact with the cam surface,
the driven means comprising an eccentric driven by the driving element,
and a lever connected to the eccentric by a pin and slot connection
and pivotally connected with the cam striker element to cause oscillation
thereof as said eccentric is driven, said pin and slot connection
providing lost motion to permit continued drive of said eccentric
when oscillation of the cam striker element is limited by contact
thereof with the cam surface;
second fluid volume recording means drivingly connected with the
cam striker element and responsive to the length of the arc of travel
of the cam striker element.
2. The device of claim 1 wherein the cam striker element has a
friction surface for contacting the cam surface.
3. The device of claim 2 wherein the cam surface is roughened.
4. The device of claim 1 wherein the pre-set limiting means which
defines the second extremity of the arc of travel of the cam striker
element comprises an adjustable stop limiting the lost motion in
the pin and slot connection.
5. The device of claim 4 wherein the adjustable stop comprises
a spring locked set screw protruding to define an effective limit
of the slot of said pin and slot connection.
6. The device of claim 1 wherein the cam striker element communicates
with a counter through the intermediary of a one way clutch, arranged
to record the arc of travel of the cam striker element in response
to the travel of the cam striker element in one direction.
7. The device of claim 6 wherein the temperature sensing means
comprises a coiled bimetallic strip and the cam surface bearing
element is a disc which rotates in response to temperature induced
rotations of the bimetallic strip, the cam surface thereof being
presented in an axial direction with respect to the axis of the
coiled bimetallic strip.
Description FIELD OF THE INVENTION
This invention relates to fluid flow measuring devices, and more
particularly to a temperature compensating device for use with a
fluid flow meter.
In gas flow meters, particularly those for industrial use required
to measure large volumes of gas being used for heating purposes,
it is necessary to allow for density changes in the gas being metered,
caused by temperature fluctuations. As the temperature rises and
the volume of gas increases, the heating capacity of a given volume
of gas is reduced. Since heating gas is normally sold to the industrial
user on the basis of a price per volume at standard temperature,
which is equivalent to a price per thermal unit of heating capacity
of the gas, suitable allowance for temperature fluctuations in the
gas volume measuring device must be made. This is conveniently accomplished
by applying automatic temperature compensation means to the meter
upon which the consumer records the volume of gas consumed.
BRIEF DESCRIPTION OF THE PRIOR ART
There are a number of criteria which a satisfactory temperature
compensating device for a gas flow meter should meet, especially
for industrial purposes. Primarily, it should function automatically
and accurately over substantial periods of time. It should require
little and infrequent maintenance and service. It should also have
some means by which its general accuracy can be checked periodically,
in simple fashion. Prior art temperature compensators for use with
gas flow meters have suffered from various defects which have rendered
them unsuitable for accurate operation over extended periods of
time. In one form, for example in U.S. Pat. No. 3581566 the arc
of travel of an indicator means, driven by the gas flow, is measured
by a measuring device, and the arc of travel is limited by a stop
positioned according to the temperature of the gas flow. Such a
device tends to give inaccurate readings after a time, due to accumulations
of dust, etc., which hinder the travel of the indicator means, and
due to wear of the parts. It is an object of the present invention
to provide an improved temperature compensating device for use with
a fluid flow meter.
SUMMARY OF THE INVENTION
The temperature compensating device of the present invention is
adapted for use with fluid flow meters, and includes means for recording
temperature corrected fluid volumes and uncorrected fluid volumes
simultaneously, so that checks on its accuracy can be readily performed.
The device of the present invention also includes features which
improve the accuracy of the performance of the device, and allow
its uninterrupted use over long periods of time with only minimal
maintenance requirements, as compared with devices previously proposed
for this purpose.
Thus according to the present invention there is provided a temperature
compensating device for use with a fluid flow meter, said device
comprising:
a driving element adapted to be driven by fluid flowing through
the meter;
first fluid volume recording means operatively associated with
said driving element to record fluid volumes flowing through the
meter;
temperature sensing means adapted to contact the fluid flowing
through the meter;
a cam surface bearing element connected to said temperature sensing
means, the position of said cam surface being determined by the
temperature sensed by the temperature sensing means;
an oscillatable cam striker element adapted to oscillate through
an arc of travel defined at the first extremity by contact with
said cam surface and at the second extremity by preset limiting
means;
the cam striker element being driven for oscillation in both directions,
into and out of contact with the cam surface, by driven means operatively
associated with said driving element;
second fluid volume recording means operatively associated with
the cam striker element and responsive to the length of the arc
of travel of the cam striker element.
The device of the invention thus has a cam striker element which
travels through an arc, the length of this arc of travel being determined
by the temperature of the flowing fluid, and the speed of travel
of the cam striker element being determined by the volume of gas
flowing through the meter in the time period, and is recorded by
suitable recording means.
In accordance with the invention, the cam striker element is positively
driven in both of its directions of oscillation through its arc
of travel. This arrangement provides enhanced accuracy over extended
periods of time in service, as compared with the use of non-positive
drive means in one or both directions such as spring urgings or
gravity feeds, since such means are apt to become inefficient and
inaccurate through contamination with dust and the like after extended
use.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In a preferred embodiment of the invention, the cam striker element
has a friction surface for contacting the cam surface, and the cam
surface is roughened. Suitably the friction surface of the cam striker
element is a sleeve of rubber or plastics material such as polyethylene,
nylon or the like, and the cam surface is roughened by the provision
of serrations thereon. Such arrangements prevent slippage between
the cam striker element and the cam surface on contact, so that
the arc of travel of the cam striker element is accurately determined
by the position of the cam surface.
Preferably also, the driving means for driving the cam striker
element for oscillation comprises an eccentric pin driven by the
driving element, and a lever connected to said eccentric pin through
a pin and slot connection and pivotally connected to the cam striker
element to cause oscillation thereof as said eccentric is driven,
said pin and slot connection providing lost motion to permit continued
drive of said eccentric when oscillation of the cam striker element
is limited by contact thereof with the cam surface.
The device of the invention may also advantageously have preset
limiting means which defines the second extremity of the arc of
travel of the cam striker element, comprising an adjustable stop
limiting the lost motion in the pin and slot connection. The adjustable
stop may comprise a spring urged set screw protruding to define
an effective limit of the slot of said pin and slot connection.
Such a set screw is thus adjusted to calibrate the instrument for
correct reading at a given temperature.
A specific preferred embodiment of the invention will now be described
with reference to the accompanying drawings, in which:
FIG. 1 is a perspective view of a temperature compensation device,
with the housing partly cut away for illustrative purposes, and
with the operative mechanism in a first position;
FIG. 2 is a perspective view of a part of the device of FIG. 1
with the operative parts in a second position.
In the drawings, like reference numerals indicate like parts.
With reference to FIG. 1 the temperature compensating device comprises
a housing 10 having an end plate 11 adapted to be secured to a duct
through which gas being metered is conveyed. The housing has secured
thereto a chassis 12 on which the operative parts for the most part
are mounted. The chassis 12 has forward and rearward upstanding
side members 12a and 12b respectively. Projecting through an aperture
in the end plate 11 and chassis 12 is a driving shaft 13 carrying
a worm gear 14 the driving shaft being coupled to a positive displacement
fluid meter (not shown) so that it is rotated by the impellor of
the meter. Worm gear 14 meshes with and drives worm wheel 15 on
a shaft 16 which is journalled in the side portions 12a and 12b
of the chassis 12 and which carries a further spur gear 17.
The device includes a gear train which is driven by spur gear 17
the gear train consisting of shafts 18 19 20 disposed parallel
to shaft 16 and journalled in the side portions of 12a and 12b of
the chassis 12. Shaft 18 carries a spur gear 21 meshing with and
driven by spur gear 17 and also meshing with and driving a spur
gear 22 mounted on shaft 19. A further spur gear 23 is mounted on
shaft 19 and thus meshes with and drives a spur gear 24 on shaft
20. The shaft 20 also carries another spur gear 25 which meshes
with a gear wheel 26 on a rev counter 27. Thus, shafts 18 19 20
and rev counter 27 are driven directly from driving shaft 13 and
worm gear 14 in response to the volume of gas flowing through the
meter, without regard to temperature.
Shaft 20 is journalled in the side members of the chassis 12 and
a portion 28 thereof extends through the forward side member 12a
of the chassis 12. Shaft portion 28 carries on its end a wheel 29
with an eccentric pin 30. The pin 30 is received in the elongated
slot 31 of a slotted lever 32 so that the pin 30 is slidably received
within the slot 31. The lever 32 is provided with a pair of apertured
projections 33 34 extending forwardly from the lever 32 at the
top and bottom of slot 31. A set screw 35 extends through the aperture
in lower projection 33 of lever 32 and is adjustable to extend
to a greater or lesser extent through apertured projection 33 the
aperture in which is appropriately screw-threaded, the set screw
extending generally parallel to slot 31 a spring 36 is located between
the head of set screw 35 and the bottom of lower projection 33
to assist in holding the set screw in its pre-determined position.
Pin 30 passes through slot 31 in lever 32 at the end remote from
wheel 29 and is pivotally received in a stop member 37. A washer
38 is interposed on pin 30 between lever 32 and stop member 37.
Projecting upwardly from stop member 37 parallel to slot 31 in
lever 32 is a generally cylindrical pin 39 which extends through
the aperture in upper projection 34 of lever 32. Pin 39 carries
a compression spring 40 urging against the lower surface of projection
34 and the upper surface of stop member 37.
At its upper end, lever 32 is pivotally connected at 41 to a cam
striker element 42. The cam striker element 42 is mounted for rotation
on a stub shaft 43 which is journalled at one end in side portion
12a of chassis 12. The cam striker 42 is connected to stub shaft
43 for drive in one direction only by means of a one-way clutch
44 mounted on shaft 43 between chassis side portion 12a and cam
striker element 42. The cam striker element 42 has a radial arm
45 provided with a rearwardly projecting finger 46 the finger 46
being covered with a sleeve 47 of plastic.
The other end of stub shaft 43 carries a radial gear wheel 48
which meshes with and drives the gear wheel 49 on the rev counter
50.
A bimetallic coiled temperature strip 51 mounted on a rod 52 is
disposed outside the housing 10 of the device, in the path of flow
of gas through the meter. Rod 52 extends through the end plate 11
of the housing 10 and carries on its end within the housing 10
a cam surface bearing element in the form of a cam wheel 53 bearing
a serrated cam surface 54 projecting axially with respect to the
rod 52. The cam wheel 53 is arranged so that serrated cam surface
54 is in the path of travel of finger 46 of cam striker element
42. Cam wheel 53 bears a visual temperature related scale 55. A
pointer 56 extends from the rev counter 50 to the vicinity of the
scale 55 so that as cam wheel 53 rotates in response to temperature
changes sensed by metallic strip 51 pointer 56 indicates the appropriate
approximate temperature on scale 55.
In operation, gas flowing through the associated gas meter (not
shown) causes rotation of the impellor of the gas meter which drives
shaft 13 which acts as a driving element for the temperature compensating
device. By means of the associated gear train and shafts 18 19
and 20 this drive is transmitted to rev counter 27 to measure actual
volume of gas flowing through the meter as previously described,
without regard to temperature. Rev counter 27 is thus a first fluid
volume recording means of the device, and is operatively associated
with shaft 13.
Bimetallic strip 51 constitutes a temperature sensing means and
contacts gas flowing through the meter and causes rotation of rod
52 and cam wheel 53 in response to the temperature of the flowing
gas. The rotational position of cam wheel 53 and hence the precise
location of serrated cam surface 54 presented to be struck by finger
46 of cam striker element 42 is thus determined by the temperature
of the flowing gas. This limits the arc of oscillation of the cam
striker element 42 as described below.
Shaft 20 is driven by the gear train from shaft 13 as previously
described, so that wheel 29 rotates counter clockwise. As it rotates,
eccentric pin 30 circles around shaft extension 28 and moves up
and down slot 31 of lever 32 causing lever 32 to pivot about its
pivotal connection 41 to cam striker element 45. As wheel 29 rotates
from its position shown in FIG. 1 towards its position shown in
FIG. 2 pin 30 moves up slot 31 carrying stop member 37 with it
and compressing spring 40 against upper projection 34. This movement
and compression causes rotation of cam striker element 42 about
stub shaft 43 from its position shown in FIG. 1 to its position
shown in FIG. 2 in which friction surface 47 on finger 46 of cam
striker element 42 contacts the appropriate location of cam surface
54 as determined by the temperature of the flowing gas. If lever
32 continues to urge cam striker element 42 to the right shown in
FIG. 2 after contact with the cam surface 54 due to rotation of
wheel 29 the motion is absorbed as lost motion by movement of pin
39 further through the aperture in upper projection 34 of lever
32 against the urging of spring 40 as pin 30 moves further up
slot 31.
As pin 30 on wheel 29 rotates further in the counter clockwise
direction, pin 30 and associated stop member 37 moves back down
slot 31 in lever 32 as a lost motion until stop member 37 comes
into contact with the end of set screw 35. When stop member 37 is
in contact with set screw 35 further movement down slot 31 is prevented
and so additional rotation of wheel 29 causes lever 32 to pull cam
striker element 42 away from cam surface 54 back to its position
shown in FIG. 1 and then the cycle is repeated, causing oscillation
of the cam striker element 42 through an arc. Thus the set screw
35 constitutes stop means limiting the arc of oscillation of cam
striker element 42 at one end, the cam surface 54 limiting the arc
of oscillation at the other end.
As cam striker 42 oscillates, one way clutch 44 disengages during
movement to the right as shown in FIG. 1 but engages during movement
to the left so as to rotate shaft 43 and drive counter 50. By this
means, counter 50 registers the arc of oscillation of cam striker
element 42 in one direction, the length of which arc is determined
by the set of screw 35 and the temperature sensed and registered
by cam surface 54. Set screw 35 is initially adjusted to calibrate
the temperature compensating device. As described, cam striker element
42 is driven in both directions, into and out of contact with the
cam surface, by the lever 32 driven from wheel 29 and shaft extension
28. |