Method of Measuring Specific Gravity and Apparatus Utilizing the Same

1. Field of the Invention

The present invention is directed to a method and apparatus for measuring specific gravity. More specifically, the present invention is directed to a method and apparatus for measuring the specific gravity of a pressurized fluid.

The present invention relates to an improved method and apparatus for measuring specific gravity of a pressurized fluid.

In accomplishing this and other objects, there has been provided, in accordance with the present invention, as method and apparatus for measuring the specific gravity of a pressurized fluid including the steps of pressurizing a fixed volume chamber by the fluid to be analyzed, allowing the pressure in the chamber to decay through a fixed restriction between predetermined pressure limits, measuring the time interval of the pressure decay between the pressure limits and converting the time interval value to the specific gravity of the fluid to be analyzed. The apparatus utilizing the aforesaid method includes a fixed volume chamber, first means for admitting a pressurized fluid to be analyzed into the chamber to pressurize the chamber to a first pressure level, second valve means for exhausting the pressurized fluid from the chamber through the fixed restriction, pressure sensing means for monitoring the pressure decay in the chamber during the exhaust of the pressurized fluid, time interval measuring means for producing a time interval value representative of the time required by the pressure decay between predetermined second and third pressure limits lower than the first pressure level and computing means for converting the time interval value to the specific gravity of the fluid to be analyzed.

A better understanding of the present invention may be had when the following detailed description is read in connection with the accompanying drawing, in which the single FIGURE is a block diagram of a specific gravity measuring apparatus utilizing the method of the present invention.

Detailed Description

Referring to the single FIGURE drawing in more detail, there is shown an apparatus for measuring the specific gravity of a pressurized fluid using the method of the present invention. An input pipeline 2 is arranged to be connected to the source of the fluid to be analyzed. The input pipeline 2 is connected through a valve 4 to a fixed volume pressure chamber 6. The valve 4 may advantageously be a solenoid operated valve having an operating solenoid 8. The pressure chamber 6 is connected to an exhaust line 10 which is connected through a second valve 12 to a fixed line restriction 14. The line restriction 14 is arranged to have an outlet 15 for exhausting the fluid to be analyzed. The second valve 12 may advantageously also be in a form of a solenoid operated valve having an operating solenoid 16.

A pressure-to-voltage transducer 18 is connected to the pressure chamber 6 to produce an output signal representative of the output pressure from the pressure chamber 6. The output signal of the transducer 18 is connected to a first input of a first comparator 20 and a first input of a second comparator 22. A second input of the first comparator 22 is connected to a source of a signal representing a second pressure level P.sub.2 while the second input of the second comparator 20 is connected to a signal source representing a third pressure level P.sub.3. The outputs of the first and second comparators 20, 22 are connected to a time interval detector 24 for determining the time interval between the output signals from the first and second comparators 20, 22. The output of the time interval detector 24 is connected to a memory 26 for storing the time interval measurements from the time interval detector 24. The data representing the time interval measurement stored in the memory 26 is arranged to be read by a microprocessor 28 for calculating the specific gravity of the fluid to be measured, as described more fully hereinafter. A display 30 which may include a printer is connected to the microprocessor 28 for recording and/or displaying the specific gravity of the fluid to be analyzed.

The apparatus shown in the single FIGURE drawing operates by pressurizing the pressure chamber 6 by the pressurized gas to be analyzed to a first pressure level P.sub.1 greater than the second pressure level P.sub.2 through the control valve 4. After the pressure chamber 6 is pressurized, the control valve 4 is closed, and the control valve 12 is opened to allow the pressure in the pressure chamber 6 to decay by exhausting the stored fluid through the restriction 14. The pressure in the pressure chamber 6 is monitored by the transducer 18 which produces an electrical output signal indicative of the pressure within the pressure chamber 6. This output signal is applied to the first and second signal comparators 20, 22 to produce an output signal from the first comparator 20 when the pressure in the pressure chamber 6 reaches the second pressure level P.sub.2 and an output from the second comparator 22 when the pressure in the pressure chamber 6 reaches a third pressure level P.sub.3. The time between the pressure levels P.sub.2 and P.sub.3 is detected by the time interval detector 24 and converted to a time interval value in a digital form, e.g., a count stored in a counter counting signals from a fixed frequency oscillator.

The digital output from the detector 24 is stored in the memory 26 which is preferably a random access memory (RAM) used to concurrently store an operating program for the microprocessor 28, which program is used, stored, read and utilized in a well-known fashion to effect a logic operation of the microprocessor 28 to calculate the specific gravity to the fluid to be analyzed and to provide the aforesaid sequentially operation of the first and second valves 8, 12. Initially, a reference fluid is supplied to the illustrated apparatus through input line 2 and its decay time (t.sub.1) is detected and stored in the memory 26. Additionally, a digital representation of the specific gravity (SG.sub.1) of the reference fluid is also stored in the memory 26. Subsequently, the illustrated apparatus is connected to a source of the fluid to be analyzed and the decay time (t.sub.2) of the fluid to be analyzed is detected and stored in the memory 26 to be used in calculating the specific gravity (SG.sub.2) of the fluid to be analyzed.

The pressure in the chamber 6 decays exponentially through the restriction 14 between P.sub.2 and P.sub.3 as follows:

Where t equals the time interval for the pressure to decay from P.sub.2 to P.sub.3 ##EQU1## where K=orifice flow constant

V.sub.o =volume of chamber 6

SG=specific gravity of the fluidpe

Assuming that V.sub.o /K is a constant for two fluids of specific gravity SG.sub.1 and SG.sub.2 :

Where t.sub.1 =time interval of decay for a fluid of specific gravity SG.sub.1 ; t.sub.2 =time interval for decay of a fluid of specific gravity SG.sub.2 ; ##EQU2##

Therefore, by measuring the decay time (t.sub.1) of a reference fluid of known specific gravity SG.sub.1, the specific gravity SG.sub.2 of another fluid can be computed from its decay time (t.sub.2) using the above final equation.

Accordingly, it may be seen, that there has been provided, in accordance with the present invention an improved method and apparatus for measuring a specific gravity of a pressurized fluid.