US 3862568 A
Gas flowmeters for indicating total volume flow. The flowmeters incorporate gravitometers having vibration densitometers including spring metal ferromagnetic cantilevered vanes which vibrate when driven.
Description (OCR text may contain errors)
United States Patent 1 1 Schlatter et a1.
[ 1 Jan. 28, 1975  Inventors: Gerald Lance Schlatter; Charles Eveleigh Miller, both of Boulder, C010.
 Assignee: International Telephone and Telegraph Corporation, New York,
 Filed: June 22, 1972  Appl. No.: 265,327
[5 [3.5. CI 73/32 A [51 Int. Cl. GOln 9/34 [58 Field of Search 73/32 A, 32 R, 30
 References Cited UNITED STATES PATENTS 1.527,?21 2/1925 Willey 73/30 1.906.985 5/1933 Marrison 310/25 X 3,002,373 10/1961 Kimmel1.... 73/30 3,117,440 1/1964 Wilner 73/32 A 3.134.035 5/1964 Grib 310/25 3.572.094 3/1971 Banks i 73/32 A 3.603.137 9/1971 Banks i 73/32 A 3.715.912 4/1971 Schlatter... 73/32 R FOREIGN PATENTS OR APPLICATIONS 9/1968 Great Britain 73/32 A Primary Examiner-James .l. Gill Attorney, Agent, or FirmA. Donald Stolzy ABSTRACT Gas flowmeters for indicating total volume flow. The flowmeters incorporate gravitometers having vibration densitometers including spring metal ferromagnetic cantilevered vanes which vibrate when driven.
A thermally conductive housing stores heat and equalizes the temperature between a gas of interest and air. The air is kept dry by a desiccator. The gas is circulated through a first chamber in the housing containing one vane. Air occupies a second chamber having another vane therein. Both chambers are vented to the atmosphere. The gas is circulated through the first chamber very slowly so that the pressures in both chambers are approximately equal to atmospheric.
In one embodiment of the gravitometer, gravity. G, is
computed in a manner similar to G =1 -DFAf,
D is a constant,
F is the ratio of ambient air temperature to ambient air pressure, and
Af, is the difference between the vane frequencies.
In another embodiment, gravity is computed in a manner similar to G 1 VAtAf where,
V is a contant, and At is the reciprocal of the difference between the air vane frequency and a vacuum frequency, f,,,
f,,= 1/t when 0. Another calculation of G is made as in G 1 DFAf,
where the F factor is incorporated by using a pressure regulator with a flexible diaphragm betweena sealed dry air chamber and a third gas chamber connected from the first chamber and vented to the atmosphere through a valve controlled by the diaphragm.
44 Claims, 34 Drawing Figures PATENTED JAN 2 8 I975 SHEEI 01 [1F 16 PATEN TED JAN 2 81975 SHEET 0? or 16 0a 287 CURRNT 7'0 PHASE D6 766 7 0/2 /24 P'Arsutmmza 3882.588 snm 11 one PATENTED JAN 2 8 I975 SHEET 12W 16 PATENTEU JAN 2 8 I975 sum 15 or 16 METHOD OF AND APPARATUS FOR PRODUCING FLUID GRAVITY AND DENSITY ANALOGS AND FLOWMETERS INCORPORATING GRAVITOMETERS BACKGROUND OF THE INVENTION This invention relates to the art of fluid measurement, and more particularly, to apparatus which may be employed in densitometers, gravitometers or flowmeters.
The word gravity is hereby defined for use herein and in the claims to mean the same thing that it conventionally means in this art, i.e., it is hereby defined to mean the ratio of the density of a gas to the density of air at the same temperature and pressure. As will be explained hereinafter, the gravity of a gas is otherwise substantially independent of temperature and pressure.
In the past, it has been the practice to measure the gravity ofa gas by loading a gas tight cylinder with a gas and placing it on a balance with a gas tight cylinder of air. This apparatus is expensive and cumbersome to use. Moreover, gravity is obtained by performing a batch process which cannot run continously with flowmeter apparatus to indicate instantaneously what the rate of volume flow and the total volume flow in a pipeline is.
SUMMARY OF THE INVENTION In accordance with the present invention, an instantaneous indication of density or gravity or signals directly proportional thereto may be obtained through the use of a vibration densitometer having a spring metal cantilevered ferromagnetic vane.
Two such densitometers may be used in a gravitometer.
In accordance with the present invention, the gravitometer thereof may be used in one or more total volume or rate of volume flow flowmeters to provide an analog output signal directly proportional to rate of volume flow. The gravitometers and flowmeters of the present invention thus have a much faster speed of response and are more accurate than gravitometers and flowmeters of the prior art.
Notwithstanding the foregoing, the gravitometers of the present invention have utility when used by themselves and not in a flowmeter. For example, the output of a gravitometer constructed in accordance with the present invention may be connected to one or more process controllers, orxto a DC. milliammeter or recorder calibrated in gravity, or any other apparatus.
Different natural gases are frequently blended to achieve a desired BTU content based on the gas gravitles.
A gravity indication is thus useful in estimating the BTU content of natural gas. It can be used in determining performance under gas delivery contracts specifying BTU content. Further, estimated BTU content is also frequently used for billing purposes.
As will be understood from the foregoing, automatic process controllers can be operated from the gravitometers of the present invention to maintain automatically any desired gravity or BTU content.
According to another feature of the invention, gravity is obtained from the beat frequency analog of a pair of vanes. An air density analog is obtained by deriving the reciprocal of a difference frequency analog which is directly proportional to the vane frequency of a vacuum minus the air vane frequency. Alternatively, a ratio of the temperature to the pressure of ambient air is obtained. If desired, a conventional phase locked loop may be employed to provide the DC. voltage analog of the beat frequency.
Another feature of the present invention resides in the unexpected use of a single power amplifier and driver coil to vibrate two vanes even though the two vanes vibrate at different frequencies.
Alternative air density analogs are provided by a gas chamber pressure control or by a T/P compensator.
Other features of the invention reside in the use of efficient apparatus for temperature equalization, desiccator apparatus to keep the air dry, and resilient mounts for isolation from extraneous vibrational interference.
The above-described and other advantages of the present invention will be better understood from the following detailed description when considered in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS In the drawings which are to be regarded as merely illustrative:
FIG. 1 is a diagrammatic view of a flowmeter;
FIG. 2 is a schematic diagram of a pickup shown in FIG. 1;
FIG. 3 is a graph of a group of waveforms characteristic of the operation of the invention shown in FIG. 1;
FIG. 4 is a diagrammatic view of a flowmeter constructed in accordance with an alternative embodiment of the present invention;
FIG. 5 is a diagrammatic view of a gravitometer;
FIG. 6 is a top plan view of a twin cell assembly indicated diagrammatically in FIG. 5;
FIG. 7 is a vertical sectional view taken on the line 7-7 through a mounting bolt shown in FIG. 6;
FIG. 8 is a vertical sectional view taken on the line 88 shown in FIG. 6;
FIG. 9 is a horizontal sectional view taken on the line 9-9 shown in FIG. 8;
FIG. 10 is a vertical sectional view taken on the line 10-10 shown in FIG. 6;
FIG. 11 is a vertical sectional view taken on the line 11-11 shown in FIG. 10;
FIG. 12 is a vertical sectional view taken on the line 12-12 shown in FIG. 6;
FIG. 13 is a horizontal sectional view taken on the line 13-13 shown in FIG. 12;
FIG. 14 is a perspective view of a ferromagnetic rod shown in FIGS. 6, 10, 11 and 12;
FIG. 15 is a vertical sectional view taken on the line 15-15 shown in FIG. 6; i
FIG. 16 is a horizontal sectional view taken on the line 16-16 shown in FIG. 15;
FIG. 17 is a schematic diagram of a portion of the circuit shown in FIG. 5;
FIG. 18 is a diagrammatic view of an alternative gravitometer constructed in accordance with the present invention;
FIG. 19 is a schematic diagram of an analog adder shown in FIG. 18;
FIG. 20 is a schematic diagram of portions of the blocks shown in FIG. 18;
FIG. 21 is a graph ofa group of waveforms characteristic of the operation of the gravitometer alternative embodiment of FIG. 18;
FIG. 22 is a block diagram of an alternative embodiment of the present invention;
FIG. 23 is a rear elevational view of a gravity cell shown in FIG. 22;
FIG. 24 is a top plan view of the cell shown in FIG. 23;
FIG. 25 is a side elevational view of the cell shown in FIG. 23;
FIG. 26 is a transverse sectional view of the cell taken on the line 26-26 shown in FIG. 23;
FIG. 27 is a vertical sectional view of the cell taken on the line 27-27 shown in FIG. 24;
FIG. 28 is a longitudinal sectional view of a conventional pressure relay;
FIG. 29 is a block diagram further illustrating the embodiment of the invention shown in FIG. 22;
FIG. 30 is a schematic diagram of a frequency-tovoltage converter;
FIGS. 31 and 32 are schematic diagrams of still another embodiment of the present invention; and
FIGS. 33 and 34 are graphs of a group of waveforms characteristic of the operation of the embodiment shown in FIGS. 31 and 32.
DESCRIPTION OF THE PREFERRED EMBODIMENTS THE FLOWMETER OF FIG. 1
It is well known in the prior art that the total flow I Q dt where t is time and Q is the volume rate of gas flow per unit time, Q being measured in standard cubic feet. This standard cubic feet (at, for example, 14.7 pounds/cubic feet pressure and 68 F.) of a gas in a pipeline may be calculated from the following equation (1) defining mass flow rate Q.
Q K PA P/TG where,
P is the static pressure in a pipeline 30 shown in FIG.
AP is the differential pressure across an orifice 32. T is the absolute temperature of the gas, and G is the gravity of the gas. The gravity, G, of a gas is defined by G Pa/Pa which is equal to a constant. Hence,
PV MRT where,
P is pressure, V is volume, M is mass, R is the gas constant, and
T is absolute temperature. If p is density, then p M/V Thus, combining (4) and (5),
p K P/T where,
Equations (8) and (9) are analogous to (6) for a gas. g, of interest and air, a.
Pg 18 a/Tu Equation (11) thus indicates that G is truly independent of which set of temperature and pressure conditions are selected.
Equation (1) may be proven as follows. The flow. 0,,
through an orifice is Ox z 8 H0 tlZ) where,
K is a constant,
A is the orifice area,
g is acceleration due to the earths gravity, and
Hg is the differential pressure head in feet across the orifice. To convert the differential head to inches of air y Hnpn/ l P p K GP/T where,
P is equal to P T is equal to T and p isequal to p Substituting p p 'into (13), (14) into the resultant, one obtains Hg I-la p aT/12 K GP Substituting (15) into (12) one obtains Q, K A 2,,H,,paT/l21( GP I Thus, I
Q. 3 JHqP where,
K, K A ,l2g/12K From expression (3) aQaITa Thus,
a a/TPa Combining (17) and (20) I o K, H p aT/GP X PT /TP,
Q K I P AP/TG where,
K ZlTaIPa and A p is equal to H p (pressure equals height times density).
The embodiment of FIG. 1 mechanizes equation (1) for continuously indicating total volume flow in standard cubic feet.
In FIG. 1, a portion of a pipeline is indicated at 30 having a disc 31 fixed therein to provide an orifice 32. A differential pressure transducer 33 senses the difference between the pressures on opposite sides of orifice 32. A static pressure transducer 34 senses the pressure on one side of orifice 32. a temperature transducer '35 senses the temperature on one side of the orifice 32.
In FIG. 1 a multiplier 36, a multiplier 37, a divider 38 and a square root extractor 39 are provided. An output circuit 40 is connected from the output of square root extractor 39. Output circuit 40 includes a pickoff 41, a saw-tooth generator 42, an inverter 43, a burst oscillator 44, a gate 45 and a counter 46.
Differential pressure transducer 33 produces a DC. current on an output lead 47 which is directly proportional to the difference between the pressures on opposite sides of the orifice 32.
Static pressure transducer 34 produces a DC. current on an output lead 48 directly proportional to the pressure on one side of orifice 32. Temperature transducer 35 produces a DC. current on an output lead 49 directly proportional to the temperature of the gas inside pipeline portion 30 on one side of orifice 32.
A gravitometer 50 is connected from pipeline portion 30 on one side of orifice 32 to produce a DC. output current on an output lead 51 directly proportional to the gravity of the gas in pipeline portion 30.
Multiplier 36 is connected from leads 49 and 51. The output of multiplier 36 is impressed upon an output lead 52 which is connected to divider 38. Multiplier 36 then produces an output current in lead 52 which is directly proportional to the product of the output currents of temperature transducer 35 and gravitometer 50.
Multiplier 37 is connected from both of the pressure transducers 33 and 34 to divider 38. Multiplier 37 has an output lead 53, the current in which is directly proportional to the product of the current outputs of the pressure transducers 33 and 34. divider 38 has an output lead 54 which carries a DC. voltage directly proportional to the output of multiplier 37 divided by the output of multiplier 36. Divider 38 may, if desired, include a current-to-voltage converter at its output. A current-to-voltage converter, for example, may be simply a resistor connected from the output of divider 38 to ground.
Notwithstanding the foregoing, any component part of the invention employed to produce a current analog may be employed to produce a voltage analog.
Square root extractor 39 has an output lead 55 upon which a DC. voltage is impressed which is directly proportional to the square root of the output of divider 38.
Pickoff 41 has an output lead 56 upon which a square wave is impressed. This square wave is generated by comparing the amplitude of the saw-tooth output of generator 42 with the amplitude of the DC. voltage on lead 55.
Inverter 43 is connected over an output lead 57 to gate 45. Inverter 43 inverts the square wave output of pickoff 41.
It is to be noted that the dimensions of a square wave are conventionally vertical in volts and horizontal in time. The word square thus has no reference to any particular relationship between the amplitude and period of such a wave. The phrase square wave is, therefore, hereby defined for use herein and in the claims to mean a rectangular wave or vice versa.
Burst oscillator 44 produces output pulses at a constant rate and at a pulse repetition frequency (PRF) which is large in comparison to the PRF of the square wave appearing on inverter output lead 57. Gate 45 is opened during the positive pulses of the square wave on