Indian Patents. 230904:"APPARATUS FOR MEASURING LOW GAUGE PRESSURE AND LOW DIFFERENTIAL PRESSURE WITH RESOLUTION APPROACHING ONE MICRON WC (10mP)"

Title of Invention	"APPARATUS FOR MEASURING LOW GAUGE PRESSURE AND LOW DIFFERENTIAL PRESSURE WITH RESOLUTION APPROACHING ONE MICRON WC (10mP)"
Abstract	An apparatus for measuring low gauge pressure and low differential pressure with resolution approaching one micron WC, said apparatus comprising: means to hold the liquid for sealing the pressure; at least one means for measuring pressure located within the means to hold the liquid; and means for transferring force connected to the means for measuring pressure for calibrating balance therein.

Full Text	Field of Invention The present invention relates to an apparatus for measuring low gauge pressure and low differential pressure with resolution approaching one micron WC (10 mP). The measurement of low AP or low gauge pressure with high resolution and accuracy is required both in industrial as well as scientific work. Low AP is generated in low flows (mass / (unit area) (unit time)) e.g., flows in big ducts, furnaces, structured packing, capillary tubes etc. These gauge pressures or differential pressures can be around fraction of mmWC and these should be measured with a system which has a resolution and accuracy at least one or two orders better than 0.1 mmWC. The usual apparatus employed are 1. Micromanometefs 2. Low range differential pressure transmitters Micromanometers are manometers with some modification to sense the small changes in the height of liquid. These modifications can be optical, two liquids with density very close to each other or inclined tube or electromagnetic type. In all such apparatus going below 0.1 mmWC is not very easy. Low range differential pressure transmitters are very common in industrial use but their resolution is also limited to 0.1 mm WC. But these instruments need calibration with instruments that have better accuracy and resolution down to 0.01 or 0.001 mmWC. Neither of the above mentioned high quality instruments is available indigenously and cost of the imported instruments can easily go to a few lacs. A similar instrument from DEBRO, Germany costs Rs.3.5 Lac. Resolution of the instrument is 0. 1 rnmWC for general measurements. Description of the related art: The usual apparatuses employed to measure low differential pressure are: 1. MICROMANOMETERS BASED ON LIQUID LEVELS: These instruments basically use displacement of liquid level and differential pressure. This displacement is amplified using several techniques, e.g., inclined tube, dual liquid and more sensitivity deflection are used to measure the change in level. These techniques can be optical, electronic or based upon acoustic or Laser interferometry. Such an apparatus becomes costlier and costlier as the techniques become more and more sensitive and specific. 2. LOW RANGE PRESSURE TRANSDUCERS: These instruments are not primary instruments. They work on change of some physical parameter with pressure. This can be resistance, capacitance, inductance or piezo electric effect. Pressure is converted to force and force is measured by the change in these parameters. Once again instrument needs calibration and its cost is high due to specific and important application. Sophistication e.g., 'Smart' or 'Intelligent' also increase the cost with relatively less benefit to the user. Accordingly, there is provided an apparatus for measuring low gauge pressure and low differential pressure with resolution approaching one micron WC, said apparatus comprising: means to hold the liquid for sealing the pressure; at least one means for measuring pressure located within the means to hold the liquid; and means for transferring force connected to the means for measuring pressure for calibrating balance therein. The apparatus tested and described measures force generated by differential pressure on an area, Force is measured using a good quality laboratory balance. A liquid is used to provide seal between the two pressures. As XF = A x AP Where A is the area on which AP is effective. Increase in area 'A results in larger force. 'A' can be considered as Amplifier's gain. The benefits of the present invention is as follows:- 1. Much higher sensitivity than the usual instruments used for the same purpose. 2. Ease of fabrication. Anybody can assemble it using plastics in a few hours time without requiring sophisticated tools. 3. Extremely low cost. 4. Linear response. 5. Calibration of the balance with standard weights is easier as compared to generating low value standard pressure. The subject invention relates to an apparatus for measuring low gauge pressure and low differential pressure with resolution approaching one micron WC, said apparatus comprising holding means to hold the liquid for sealing the pressure; at least one pressure measuring means for measuring pressure located within the means to hold the liquid; and force transferring means for transferring force connected to the said pressure measuring means for calibrating balance therein. Brief description of the accompanying drawings; - The Apparatus of the present invention consists of three vessels A, B, C of diameters DA> DB > DC. Vessel A holds the liquid for sealing the pressures. Vessel B and C make two chambers to which pressures to be measured are connected. Force is generated due to differential pressure across vessel C. This force F = n Dc2 x (Pb - PC) This force is transferred to the balance through suitable links. If only gauge pressure is to be measured then vessel B is redundant. The factors, which can affect the accuracy and resolution, are 1. Changes in the calibration of balance. 2. Effect of ambient temperature on 'Dc' diameter of the measuring vessel. It will affect the calibration. 3. Sticking of liquid to surface of measuring vessel C when liquid moves in or out. It will affect the zero adjustment. 4. Effect of buoyancy changes due to changes in the liquid height in the measuring vessel. It will affect the linearity. 5. Changes in the surface tension and contact angle of the surface, of vessel 'C', which comes in contact with liquid. It will affect the zero adjustment. 6. Condensation of sealing liquid on vessel C. It will affect zero of the instrument. A high quality balance with built in calibration and master weights are required to avoid problems due to changes in the calibration of balance as mentioned 'in '1' above. Measuring vessel should be thin walled and of material for which co- efficient of Thermal Expansion is very small e.g., Invar. The surface of this vessel, which is to come in contact with the sealing liquid, should be coated with Teflon. These changes will reduce the effects mentioned in 3,4 and 5 above. For higher AP mercury can be used as a sealing liquid. The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. WE CLAIM;- 1. An apparatus for measuring low gauge pressure and low differential pressure with resolution approaching one micron WC, said apparatus comprising: holding means to hold the liquid for sealing the pressure; at least one pressure measuring means for measuring pressure located within the means to hold the liquid; and force transferring means for transferring force connected to the said pressure measuring means for calibrating balance therein. 2. An apparatus as claimed in claim 1, wherein said pressure measuring means for measuring pressure is connected to another pressure measuring means thereby making two chambers. 3. An apparatus as claimed in claim 1 or 2, wherein said pressure measuring means is located on a supporting means which inturn is connected to a balancing means to avoid problems due to changes in the calibration of balance. 4. An apparatus as claimed in claim 3, wherein said balancing means has built in calibration and master weights. 5. An apparatus as claimed in claim 3, wherein said pressure measuring means is thin walled having thickness of O.lmm to 0.5mm and is made up of material selected from glass, low thermal Co-efficient stainless steel. 6. An apparatus as claimed in claim 5, wherein said material is Invar. 7. An apparatus as claimed in claim 6, wherein surface of the said pressure measuring means is coated with Teflon. 8. An apparatus as claimed in claim 1, wherein said liquid is mercury. 9. An apparatus for measuring low gauge pressure and low differential pressure with resolution approaching one micron WC, substantially as herein described with reference to the accompanying drawings.

Full Text

Field of Invention
The present invention relates to an apparatus for measuring low gauge pressure and low differential pressure with resolution approaching one micron WC (10 mP). The measurement of low AP or low gauge pressure with high resolution and accuracy is required both in industrial as well as scientific work. Low AP is generated in low flows (mass / (unit area) (unit time)) e.g., flows in big ducts, furnaces, structured packing, capillary tubes etc. These gauge pressures or differential pressures can be around fraction of mmWC and these should be measured with a system which has a resolution and accuracy at least one or two orders better than 0.1 mmWC.
The usual apparatus employed are
1. Micromanometefs
2. Low range differential pressure transmitters
Micromanometers are manometers with some modification to sense the small changes in the height of liquid. These modifications can be optical, two liquids with density very close to each other or inclined tube or electromagnetic type. In all such apparatus going below 0.1 mmWC is not very easy. Low range differential pressure transmitters are very common in industrial use but their resolution is also limited to 0.1 mm WC. But these instruments need calibration with instruments that have better accuracy and resolution down to 0.01 or 0.001 mmWC.
Neither of the above mentioned high quality instruments is available indigenously and cost of the imported instruments can easily go to a few lacs. A similar instrument from DEBRO, Germany costs Rs.3.5 Lac. Resolution of the instrument is 0. 1 rnmWC for general measurements.
Description of the related art:
The usual apparatuses employed to measure low differential pressure are:
1. MICROMANOMETERS BASED ON LIQUID LEVELS:
These instruments basically use displacement of liquid level and differential pressure. This displacement is amplified using several techniques, e.g., inclined tube, dual liquid and more sensitivity deflection are used to measure the change in level. These techniques can be optical, electronic or based upon acoustic or Laser interferometry.
Such an apparatus becomes costlier and costlier as the techniques become more and more sensitive and specific.
2. LOW RANGE PRESSURE TRANSDUCERS:
These instruments are not primary instruments. They work on change of some physical parameter with pressure. This can be resistance, capacitance, inductance or piezo electric effect. Pressure is converted to force and force is measured by the change in these parameters. Once again instrument needs calibration and its cost is high due to specific and important application. Sophistication e.g., 'Smart' or 'Intelligent' also increase the cost with relatively less benefit to the user.
Accordingly, there is provided an apparatus for measuring low gauge pressure and low differential pressure with resolution approaching one micron WC, said apparatus comprising:
means to hold the liquid for sealing the pressure;
at least one means for measuring pressure located within the means to hold the
liquid; and
means for transferring force connected to the means for measuring pressure for calibrating balance therein.
The apparatus tested and described measures force generated by differential pressure on an area, Force is measured using a good quality laboratory balance. A

liquid is used to provide seal between the two pressures.
As XF = A x AP Where A is the area on which AP is effective. Increase
in area 'A results in larger force. 'A' can be considered as Amplifier's gain.
The benefits of the present invention is as follows:-
1. Much higher sensitivity than the usual instruments used for the same purpose.
2. Ease of fabrication. Anybody can assemble it using plastics in a few hours time
without requiring sophisticated tools.
3. Extremely low cost.
4. Linear response.
5. Calibration of the balance with standard weights is easier as compared to
generating low value standard pressure.
The subject invention relates to an apparatus for measuring low gauge pressure and low differential pressure with resolution approaching one micron WC, said apparatus comprising holding means to hold the liquid for sealing the pressure; at least one pressure measuring means for measuring pressure located within the means to hold the liquid; and force transferring means for transferring force connected to the said pressure measuring means for calibrating balance therein.
Brief description of the accompanying drawings; -
The Apparatus of the present invention consists of three vessels A, B, C of diameters DA> DB > DC. Vessel A holds the liquid for sealing the pressures. Vessel B and C make two chambers to which pressures to be measured are connected.
Force is generated due to differential pressure across vessel C. This force F = n Dc2 x (Pb - PC)
This force is transferred to the balance through suitable links.
If only gauge pressure is to be measured then vessel B is redundant.
The factors, which can affect the accuracy and resolution, are
1. Changes in the calibration of balance.
2. Effect of ambient temperature on 'Dc' diameter of the measuring vessel. It will
affect the calibration.
3. Sticking of liquid to surface of measuring vessel C when liquid moves in or out.
It will affect the zero adjustment.
4. Effect of buoyancy changes due to changes in the liquid height in the
measuring vessel. It will affect the linearity.
5. Changes in the surface tension and contact angle of the surface, of vessel 'C',
which comes in contact with liquid. It will affect the zero adjustment.
6. Condensation of sealing liquid on vessel C. It will affect zero of the instrument.
A high quality balance with built in calibration and master weights are required to avoid problems due to changes in the calibration of balance as mentioned 'in '1' above.
Measuring vessel should be thin walled and of material for which co-
efficient of Thermal Expansion is very small e.g., Invar. The surface of this vessel, which is to come in contact with the sealing liquid, should be coated with Teflon. These changes will reduce the effects mentioned in 3,4 and 5 above. For higher AP mercury can be used as a sealing liquid.
The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

WE CLAIM;-
1. An apparatus for measuring low gauge pressure and low differential
pressure with resolution approaching one micron WC, said apparatus
comprising:
holding means to hold the liquid for sealing the pressure;
at least one pressure measuring means for measuring pressure located
within the means to hold the liquid; and
force transferring means for transferring force connected to the said
pressure measuring means for calibrating balance therein.
2. An apparatus as claimed in claim 1, wherein said pressure measuring
means for measuring pressure is connected to another pressure
measuring means thereby making two chambers.
3. An apparatus as claimed in claim 1 or 2, wherein said pressure
measuring means is located on a supporting means which inturn is
connected to a balancing means to avoid problems due to changes in the
calibration of balance.
4. An apparatus as claimed in claim 3, wherein said balancing means has
built in calibration and master weights.
5. An apparatus as claimed in claim 3, wherein said pressure measuring
means is thin walled having thickness of O.lmm to 0.5mm and is made
up of material selected from glass, low thermal Co-efficient stainless
steel.
6. An apparatus as claimed in claim 5, wherein said material is Invar.
7. An apparatus as claimed in claim 6, wherein surface of the said pressure
measuring means is coated with Teflon.
8. An apparatus as claimed in claim 1, wherein said liquid is mercury.
9. An apparatus for measuring low gauge pressure and low differential
pressure with resolution approaching one micron WC, substantially as
herein described with reference to the accompanying drawings.

Documents:

598-del-2000-abstract.pdf

598-del-2000-claims.pdf

598-del-2000-correspondence-others.pdf

598-del-2000-correspondence-po.pdf

598-del-2000-description (complete).pdf

598-del-2000-drawings.pdf

598-del-2000-form-1.pdf

598-del-2000-form-13.pdf

598-del-2000-form-19.pdf

598-del-2000-form-2.pdf

598-del-2000-form-3.pdf

598-del-2000-gpa.pdf

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Patent Number

230904

Indian Patent Application Number

598/DEL/2000

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

28-Feb-2009

Date of Filing

16-Jun-2000

Name of Patentee

ENGINEERS INDIA LIMITED

Applicant Address

ENGINEERS INDIA BHAWAN, 1, BHIKAJI CAMA PLACE, NEW DELHI, 110066, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	HAR SUKHDEEP SINGH	ENGINEERS INDIA LIMITED, ENGINEERS INDIA BHAWAN, 1, BHIKAJI CAMA PLACE, NEW DELHI, 110066, INDIA.
2	DR. BHUPINDER SINGH GILL	ENGINEERS INDIA LIMITED, ENGINEERS INDIA BHAWAN, 1, BHIKAJI CAMA PLACE, NEW DELHI, 110066, INDIA.

PCT International Classification Number

G01F 1/34

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA