GB2327760A

GB2327760A - Gas displacement volume measurement apparatus

Info

Publication number: GB2327760A
Application number: GB9715425A
Authority: GB
Inventors: Arthur Desmond Haigh; Frank Thompson
Original assignee: University of Manchester Institute of Science and Technology (UMIST); University of Manchester
Current assignee: University of Manchester Institute of Science and Technology (UMIST); University of Manchester
Priority date: 1997-07-23
Filing date: 1997-07-23
Publication date: 1999-02-03
Also published as: GB9715425D0

Abstract

A gas displacement volume measurement apparatus comprising a differential pressure transducer 3. A first chamber (1) of the apparatus is in communication with a first input to the transducer for receiving an object (13) the volume of which is to be measured. A second chamber (4) of the apparatus is in communication with a second input to the transducer. Means are provided for simultaneously modifying the volumes of the first and second chambers (14) by predetermined amounts. Means are provided for calculating the volume of the object from an output of the transducer representative of the differential pressure between the first and second inputs.

Description

GAS DISPLACEMENT VOLUME MEASUREMENT METHOD AND APPARATUS This invention relates to a gas displacement volume measurement method and apparatus, and particularly although not exclusively to a method and apparatus for measuring the volume of grain kernels.

The accurate measurement of properties of grain kernels is of considerable commercial interest to both plant breeding laboratories and grain processing plants.

Several parameters are commonly used to describe grain kernels; these are hardness, protein content, pasting, mass, and density. Density is a particularly important parameter, but in practice is difficult to measure accurately.

One known method of density measurement comprises filling a container of known volume with grain kernels and then weighing the container. This method involves an estimation of a filling parameter of the grain, and is therefore inherently inaccurate.

A second known method of density determination involves measuring the volume of a single kernel by determining the dimensions (length, width and height) of a kernel using two closed circuit digital cameras viewing the kernel from mutually perpendicular directions, calculating the volume from those dimensions assuming the kemel has a regular ellipsoidal shape, and then dividing the volume by the mass of the kernel. The accuracy of this method is limited by the irregular shape of grain kernels.

Since it is a simple matter to determine the mass of a grain kernel, an accurate determination of the volume of a kernel will allow an accurate measurement of its density to be obtained.

It is an object of the present invention to provide a volume measurement method and apparatus which overcomes or substantially mitigates the above disadvantages.

According to the invention there is provided a gas displacement volume measurement apparatus comprising a differential pressure transducer, a first chamber in communication with a first input to the transducer for receiving an object the volume of which is to be measured, a second chamber in communication with a second input to the transducer, means for simultaneously modifying the volumes of the first and second chambers by predetermined amounts, and means for calculating the volume of the object from an output of the transducer representative of the differential pressure between the first and second inputs.

Preferably, the volume modifying means comprises a piston located in a cylinder, each chamber being defined by the space defined within the cylinder.

Preferably, the volume modifying means is arranged to allow each volume to be modified by a fixed amount only.

Preferably, the combined volume of the first chamber and the first input to the transducer is equal to the combined volume of the second chamber and the second input to the transducer, the volume modifying means being arranged to modify the volumes of the first and second chambers by equal amounts.

Preferably, a cavity of variable volume is provided adjacent one of the chambers to allow the combined volumes of the apparatus at either side of the transducer to be equalised.

The invention also provides a method of gas displacement volume measurement comprising inserting an object the volume of which is to be measured into a first chamber in communication with a first input to a differential pressure transducer, connecting a second input to the transducer to a second chamber, simultaneously modifying the volumes of the first and second chambers by predetermined amounts, and calculating the volume of the object from an output of the transducer representative of the differential pressure between the first and second inputs.

Preferably, the volumes of the first and second chambers are modified by inserting pistons into cylinders defining the chambers.

Preferably, the volumes of the first and second chambers are each modified by fixed amounts.

Preferably, a calibration curve is obtained by performing the volume measurement on objects of known volume.

Preferably, the combined volume of the first chamber and the first input to the transducer is equal to the combined volume of the second chamber and the second input to the transducer, and the volumes of the first and second chambers are modified by equal amounts.

Specific embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a gas displacement volume measurement apparatus according to a first embodiment of the invention; Figure 2 is a graph illustrating the performance of the measurement apparatus of Figure 1; and Figure 3 is a schematic view of a gas displacement volume measurement apparatus according to a second embodiment of the invention.

Referring to Figure 1, a gas displacement volume measurement apparatus comprises a first chamber 1 connected via tubing 2 to one side of a differential pressure transducer 3, and a second chamber 4 connected via tubing 5 to a second side of the differential pressure transducer 3. The tubing 2 and 5 and pressure transducer 3 are located within a glass filled nylon body 6. The chambers 1 and 4 are located over protrusions from the body 6 which receive the tubing 2 and 5. The chamber-defining tubes form an airtight seal with the body 6.

The pressure transducer 3 is a silicon diaphragm differential pressure transducer from the 132SC series made by Sensyn and available from Farnell Components. The transducer 3 is mounted on aluminium plates 7, 8 which are located over terminations of the tubing 2, 5. Each plate 7, 8 is attached to the body 6 using airtight RTV seals 9 made by room temperature vulcanising. Each plate 7, 8 is provided with a hole 10, 11 at its centre to allow the communication of pressure within the tubing 2, 5 to the pressure transducer 3. Signals from the transducer 3 pass to output leads 12 which are connected to a meter (not shown).

In use, a grain kernel 13 is inserted into one chamber 1. Pistons 14 are located in each chamber 1, 4, the pistons 14 being connected such that they each penetrate an equal distance into the chambers 1, 4. The pistons 14 are inserted a pre-determined distance into the chambers 1, 4 and a voltage reading corresponding to a differential pressure at the transducer 3 is displayed by the meter (not shown).

The apparatus is based on the application of the ideal gas equation: pV = nRT where p is the pressure in Pascals, V is the volume in m3, n is the quantity of gas in moles, R is the universal gas constant 8.341 J mol IK-', and T is the temperature in K.

The differential pressure Pk at the transducer 3 when each volume is modified by AV with a grain kernel in the first chamber 1 is: n1RT n,RT V AVVk v2-AV where subscripts 1 and 2 denote values of volume and gas quantity at either side of the transducer 3, and Vk is the volume of the grain kernel.

Referring now to Figure 2, the volume of a grain kernel may be derived from voltage signals at the meter using a graph showing volume versus voltage. The graph was obtained by making pressure measurements using samples of known volume.

The gradient of the graph shown in Figure 2 will vary with the temperature of the apparatus. Calibration points obtained for different operating temperatures are thus needed to prevent volume measurements being influenced by temperature changes.

The apparatus allows grain kernel volume measurements to be performed without requiring an accurate determination of the volume of either chamber 1, 4, or an accurate determination of the displacement of the pistons 14. It will be apparent however that calibrated measurements will only be obtained if the displacements of the pistons are fixed. This may be ensured by positioning end stops on the pistons 14.

It will be apparent to a skilled person that it is not necessary to the operation of the invention that chambers 1 and 4 be of equal volume. Furthermore, it is not necessary that the volumes of chambers 1 and 4 are modified by equal amounts.

An alternative embodiment of the invention is shown in Figure 3. The reference numerals used in Figure 1 are used in Figure 3 to depict identical components of the apparatus. The embodiment of Figure 3 has the same configuration of first and second chambers 1, 4 and differential pressure transducer 3 as the embodiment shown in Figure 1. A secondary housing 15 is located between the first and second chambers and the nylon body 6. Within the secondary housing 15 the tubing 2 which connects the first chamber 1 to the transducer 3 opens into a cavity of variable volume 16. The dotted lines indicate the maximum volume of the cavity 16.

The volume of the cavity 16 is modified until the volumes of the apparatus on each side of the transducer are the same. A differential pressure measurement taken with no grain kernel in the first chamber 1 will result in a zero differential pressure reading when the volumes of each side of the apparatus are matched.

The embodiment of the invention shown in Figure 3 is advantageous in that it is not affected by temperature variations. This is because variations in gas density caused by temperature changes will have an equal effect on either side of the pressure transducer when the volumes of each side of the apparatus are matched. In order to maintain temperature independence, the volumes of the first and second chambers 1, 4 must be modified by equal amounts during measurement.

The apparatus is operated in an identical manner to the apparatus depicted in Figure 1, except that only one calibration curve is needed to convert voltages into volume measurements, provided that the volumes of each side of the apparatus remain matched.

Once the volume of a grain kernel has been determined, its density may be found by dividing the mass of the kernel by its volume.

Claims

1. A gas displacement volume measurement apparatus comprising a differential pressure transducer, a first chamber in communication with a first input to the transducer for receiving an object the volume of which is to be measured, a second chamber in communication with a second input to the transducer, means for simultaneously modifying the volumes of the first and second chambers by predetermined amounts, and means for calculating the volume of the object from an output of the transducer representative of the differential pressure between the first and second inputs.

2. A volume measurement apparatus according to claim 1, wherein the volume modifying means comprises a piston located in a cylinder, each chamber being defined by the space defined within the cylinder.

3. A volume measurement apparatus according to claim 1 or 2, wherein the volume modifying means is arranged to allow each volume to be modified by a fixed amount only.

4. A volume measuring apparatus according to any previous claim, wherein the combined volume of the first chamber and the first input to the transducer is equal to the combined volume of the second chamber and the second input to the transducer, the volume modifying means being arranged to modify the volumes of the first and second chambers by equal amounts.

5. A volume measuring apparatus according to claim 4, wherein a cavity of variable volume is provided adjacent one of the chambers to allow the combined volumes of the apparatus at either side of the transducer to be equalised.

6. A method of gas displacement volume measurement comprising inserting an object the volume of which is to be measured into a first chamber in communication with a first input to a differential pressure transducer, connecting a second input to the transducer to a second chamber, simultaneously modifying the volumes of the first and second chambers by predetermined amounts, and calculating the volume of the object from an output of the transducer representative of the differential pressure between the first and second inputs.

7. A method of volume measurement according to claim 6, wherein the volumes of the first and second chambers are modified by inserting pistons into cylinders defining the chambers.

8. A method of volume measurement according to claim 6 or 7, wherein the volumes of the first and second chambers are each modified by fixed amounts.

9. A method of volume measurement according to any of claims 6 to 8, wherein a calibration curve is obtained by performing the volume measurement on objects of known volume.

10. A method of volume measurement according to any of claims 6 to 9, wherein the combined volume of the first chamber and the first input to the transducer is equal to the combined volume of the second chamber and the second input to the transducer, and a measurement is performed by modifying the volumes of the first and second chambers by equal amounts.

11. A gas displacement volume measurement apparatus substantially as hereinbefore described with reference to the accompanying drawings.

12. A method of gas displacement volume measurement substantially as hereinbefore described with reference to the accompanying drawings.