Title of Invention

A DIGITAL MICRO MANOMETER TO MEASURE VERY LOW DIFFERENTIAL PRESSURE HEADS

Abstract

ABSTRACT Disclosed herein is a digital micro manometer (Fig.l) to measure very low differential pressure heads with high accuracy. The micro manometer of the present invention has digital display along with a provision of continuous monitoring and recording data on to a computer. Further the micro manometer of the present invention has inbuilt calibration facility and the same is quick in responding.

Full Text

This invention relates to a Digital Micro Manometer to measure very low differential pressure heads. Present state of the art: Digital micro manometers are highly essential in experimental research or other wise in laboratories, industries or in field. Such measuring equipments which are economical, reliable, accurate with a high resolution, quick responsive, inbuilt calibration facility, easy to use and maintain, as well as with a digital display along with a provision of continuous monitoring and recording data on to a computer are not available at present in the market. As such there is no micro manometer which will simultaneously satisfy all the requirements, Therefore, micro manometers have to be developed to meet all such qualities/requirements to a great extent and particularly useful for the measurement of low differential heads in research laboratories and in industries. Limitations: Low pressure measurements tire generally tough but they are very essential in experimental research. As such micro manometers are not available at an affordable cost, researchers are adopting less accurate and less reliable manometers such as inclined manometers, differential density (manometric fluids) manometers etc., even to measure low differential pressure heads. The micro manometers claimed here is useful to measure low differential pressure heads in the range of few millimeters of Hg, but with a resolution ofeither 0.01mm or 0.001 mmofHg. Proposed solutions: In experimental investigations either in hydraulic or aerodynamic laboratories measurement of small pressure variations with high accuracy is extremely important. Hence micro manometers are needed to measure such small pressure heads. A product is designed and developed to meet such requirements. This invention will now be described with reference to the accompanying drawmgs, wherein: Fig. 1 is a schematic diagram of the digital micro manometer of the present invention; and Fig. 2 is a block schematic diagram of signal processing of the capacitive transducer circuit. hi Fig.l, Si. Sj, S3 and S4 are the four cylindrical glass sumps. Sump Si is connected with a higher pressure P| through cock Ci while sump S4 is connected with a lower pressure of P2 through cock C2. Cock C3 controls S3. The applied differential pressure head AH is obtained by (PrPiVy where y is the unit weight of the experimental fluid in the sump. 1,2,3 and 4 represent the distances AZi, AZ2, AZ3 and AZ4 respectively where AZi is the distance by which the level of manometric fluid (of weight Ymi) in S| is lowered and AZ2 is the distance by which level in S2 rises due to the application of differential pressure, hi S3 and S4, level of manometric fluid (of weight yni2) is respectively lowered by AZ3 and rises by AZ4. Probe M on top of S2 measures the air gap AR between the mercury meniscus in S2 and itself. G provides the grounding for the merciuy meniscus. In Fig.2, the signal input is provided to a fixed capacitor in a detector circuit. The output of the detector is fed to an AC-DC converter circuit. The signal then passes through several filter-amplifier stages to obtain a stable DC output in the final stage. Objects of the present invention: Accordingly, the primary object of the invention is to design and develop a micro manometer, which will measure very small pressure variations with high accuracy. Such pressure variations are either termed as instantaneous values like turbulent fluctuations or as quasi-steady state (time averaged) values. It is a further object of the present invention to design a micro manometer, which is economical, reliable and accurate with high resolution as well as easy to use and maintain. Yet another object of the present invention is to provide a micro manometer, which has digital display along with a provision of continuous monitoring and recording data on to a computer. Further the micro manometer of the present invention has inbuilt calibration facility and the same is quick in respondmg. This invention thus provides a Digital Micro Manometer shown schematically in Figure 1, comprising: (a) a manometer circuit consisting of four interconnected cylindrical sumps Si, S2, S3 and S4 for holding experimental fluids through which differential pressures are applied; the said sumps are being provided with suitable means to induct sufficient quantities of manometric fluids; a probe M is provided at the top of sump S2 for measuring the air gap between the mercury meniscus and itself; and (b) a capacitive transducer means to measure accurately and display digitally the air gap AR in terms of AZ2, from which the differential head, AH is determined. The differential head, AH is determined by the following 'eoveming equation': AH=AZ2[(Y™i-Ya)/7w+(A2/Ai)(yn.i-y)/Yw+(A2/A3)(Yn^-Ya)/Yw+(A2/A4)(Y«2-yVYw] in which y^ is the unit weight of water, ymi, Ym2. are the unit weight of the manometric fluid in sumps Si & S2 and S3 & S4 respectively, y^ is the unit weight of air, and y is the unit weight of the experimental fluid and AZi is the change in distance which is consequent to the application of the differential pressure. DETAILED DESCRIPTION OF THE PRODUCT: CompoDent-I: Manometer Circuit: The micro-manometer consists of four cylindrical glass sumps, Sj, S2, S3 and 84 as shown in Fig. 1. All the sunqjs are of uniform cross-sectional areas of Ai, A2, A3 and A4 respectively. The sumps S| and S2 as well as S4 and S3 are connected at their bottom where as the sumps S2 and S3 are connected at the top as shown in Fig. 1. The Sump Si is connected with a higher pressure Pi, where as the sump S4 is connected with a lower pressure of P2. Thus the applied differential pressure head is, AH = Hi-H2 = (Pi-P2)/7 (1) Where, y is the unit weight of the experimental fluid. The micro-manometer is expected to measure and display the differential pressure head, AH with highest possible accuracy. Before supplying the differential pressure, the sumps S\ and S2 are filled with a heavier liquid (mercury) of unit weight ymu where as the sumps S3 and S4 are filled with another heavier liquid of unit weight Ym2- Air, of unit weight ya, is trapped on the top of the sumps S2 and S3. Let the levels of manometric fluids stand at a datum of 0-0, before the application of differential pressure as shown in Fig. 1. The cocks Ci.Cj and C3 can be used appropriately to induct sufficient quantities of manometric fluids and to apply differential pressures as well as to remove any air bubbles in the experimental fluids. A probe, M, which measures the air gap between the mercury meniscus and itself, is rigidly fixed at the top of the sump S2 such that there is fi^e communication of pressure through £ur in the sumps S2 and S3. However, sufficient gap is provided between the level O-O and the probe M to facilitate a free vertical movement of mercury level as per the applied differential pressure intensity. In the present arrangement the maximum gap provided is ranging from 2 mm to about 10 mm, thus the range of differential head that can be measured is about 2mm to 10mm of Hg. Component-II: Capacitive Transducer: A precise displacement measuring device based on variable capacitance principle with a non-contact type transducer is developed and used to measure the air gap, AR between probe, M and the mercury level in sump S2. In some cases mercury is avoided (to reduce cost of the product) and it is replaced by water (in place of mercury in sumps Sj and S2) and in such a situation a metallic float is used as a moving plate in the capacitance circuit. Thus either mercury or metallic float serve as a moving plate and probe M as a fixed plate of a capacitor. The capacitance between two paraUel conductive plates in an electrical circuit varies with the distance between the plates in a fixed relation to the change in distance. In the present micro-manometer the mercury meniscus acts as one plate (grounded through G for the purpose) and the probe, M as the other plate, which is kept parallel to the meniscus. If float is used same grounding procedure is adopted. The capacitance between the transducer probe, M and the mercury meniscus is detected and compared with a fixed capacitor in a detector circuit. The output of the detector circuit is fed to an AC-DC converter circuit, and then passes through several filter stages. A stable DC output is obtained at the last stage. This DC voltage is fed to a digital display, which displays the distance between the transducer and mercury meniscus directly in mm. Block schematic diagram of the mstrument is shown in Fig. 2. Turbulent fluctuations in the experimental fluid flow are expected to transmit through the manometric circuit and finally in to the signal output. Provisions are made for coimecting the signal output to a recorder, oscilloscope or data acquisition system. Thus it is possible to record the turbulent fluctuations in the experimental fluid flow. On the other hand, for recording the quasi-steady state (time averaged) pressure changes, provisions are made in the circuit to suppress such minor and continuous fluctuations in the signal to get a stable readable display. The instrument has a range of about 2 mm to lOtnm and a resolution of about either 0.01 or 0.001 mm. It may be noted that the range of measurement can be increased by increasing the cross sectional area of the probe, M as well as the cross- sectional area of the sump, S2 according to capacitance principle. The operating range of temperature is about 8°C to 40°C. Componeot-ni: Working Principle: Due to the application of differential pressure, the level of manometric fluid (of unit weight Ymi) in sump Si lowers by a distance of AZ|, where as its level in sump S2 rises by AZ2 compared the datum 0~0. As a consequence, the levels of the manometric fluid (of unit weight yra2) in sumps S3 and S4 have to under go a change such that it lowers by AZ3 and rises by AZ4 in the respective sumps. As the volumetric displacement in each of the sumps is the same, the following expression is valid. AiAZ|= A2AZ2= A3AZ3= A4AZ4= a constant (2) Where, Ai, A2, A3 and A4 are the cross-sectional areas of the sumps Si, S2, S3 and 84 respectively. The following general expression can be derived for the differential pressure head, AH in terms of water, while balancing the pressures at various levels in the manometer circuit. AH=AZ2[(Y™I -ya)/Y*+(A2/A,)(Ym. -Y)/Yw+(A2/A3)(y^-Ya)/rw+(A2/A4)(Y„^-Y)/Yw] (3) Above equation is the general working principle, may also be called as general governing equation of the micro manometer. hi Eq.3, Yw is the unit weight of water. (One may prefer to express the differential pressure head, AH in terms of mercury then unit weight of mercury, Ym, has to be used in place of Yw)- The value of terms inside the square brackets is called as the 'manometer constant', CM and hence Eq.3 can be expressed as follows. AH = CM AZ2 (3a) The probe M measures the air gap, AR, between the mercury meniscus (or a metallic float) and itself, as shown in Fig. 1. The capacitive transducers developed at present, covers the range of AR from about 2mm to 10 mm with a resolution of about either 0.01mm or 0.001 mm. It may be noted that as AR reduces there is an increase in AZ2 and vice versa and thus there exists a direct relation between AZi and AR. Therefore, one may say that the capacitive transduces measures indirectly the relative changes in AZ2. Variety of Models: By making use of the working principle or governing Eq.3, a good variety of micro manometers can be designed to cater or satisfy various needs- in terms of instrument's resolution/accuracy, range of measurement, and even to consider the economy and maintenance etc. Only some of them are presented in the Table 1 with illustrations for their use either in water or air as experimental fluid under the following assumed conditions: In all such models, the cross-sectional area of all the sumps, except S2, are the same and is equal to A, where as the sump S2 is of area equal to a. Thus the conditions, A]= A3 = A4 =A and A2 = a, are considered along with the imit weights of manometric fluids used (as shown in the Table) while obtaining the equations given in the last column. Illustration of First Model: Model-IA and IB; In this model mercury is used as manometric liquid in all the sumps, thus ya,i = Ym2 = Ym, the unit weight of mercury. Also the cross-sectional areas of the sumps S], S3 and S4are equal to A i.e., A| = A3 = A4 = A, where as the sump S2, containing the probe M, is of a relatively smaller cross sectional area, A2 = a. The unit weight of air in sump S2 and S3, at their top, is ya. In this model both water and air can be used as experimental or working fluid. If water is taken as the experimental fluid, then y =YW, unit weight of water, and a governing equation for this model can be deduced from Eq. 3, as AH = AZ2 [(l+a/A)(y„ -Ya)/yw + (2a/A)(ywy* -I)] (4) The usefulness of the above equation can best be illustrated by using certain numerical values. Thus, by taking values of a/AsO.l, yn^l3.6 ^nfcm^, yw^l gmi/cm^ and ya si .2x10"^ gmficm the value of manometer constant. CM = 17.5. Let AZ2 is measured with an accuracy of 0.001mm, then the differential head, AH can be measured with an accuracy of 0.0175 mm of water head, or about 1.69 microbar. This is reasonably a sufficient accuracy of measurement for most problems {with low pressure heads) in pipe and open-channel flow experiments. Let the design value of AZ2 is up to a maximum of lOmm, ^e rsuige of the differential head AH that can be measured in this model is up to 175 mm of water head with an accuracy of 0.0175 mm. In general, the measurement accuracy of AH can be increased, by decreasing the value of a/A; where as the range of AH decreases. It may be noted here that air can be used as experimental fluid (y = ya) instead of water. An appropriate equation similar to Eq. 4 (by substituting ymi = ym2 = Ym ; Y = Ya; Ai = A3 = A4 = A and A2 = a in Eq.3) can be derived from the general Eq. 3, as AH = AZi [(l+3a/A)(y« -ya)/yw] (4a) Where AH is the differential head in terms of water. The major advantage of the furst model (models lA&B) is such that the turbulent fluctuations in the experimental fluid are significantly dampened due to the presence of heavier manometric fluid of mercury in all die four sumps and hence the signal output (as seen in the digital display) is stable. The major disadvantage is the increased cost of the manometer due to large amounts of expensive mercury in all the foui sumps. In the next models attempts are made to reduce or totally avoid the use of mercury in the sumps there by reducing the cost of making the micro-manometers. Illustration of Second Model: Model-2A and 2B: In this model the usage of mercury is reduced to half when compared to the first model and water is used as the experimental fluid. Here, mercury is avoided in the sumps, Sj and S4 by allowing the experimental fluid to fill in those two sumps. Except this change, all are kept identical to thefirstmodel. Hence by making use ofYnii = ym,Yni2 = Yw, and 7 = 7w following governing equation for this second model, for water as the experimental fluid, is obtained as, AH = AZ2 [(l+a/A)(y„ -yaVYw] (5) The usefuhiess of the above equation can best be illustrated by using certain numerical values. Thus by taking values of a/AsO.l, YmSl3.6 gmfcm^, YWSI gmfi'cm^ and ya Sl.2xl0'^ gmfcm^ the value of manometer constant is, CM = 15. The accuracy of AH measurement is s0.015 ram of water head and its range is up to a maximum of 150mm, if AZ2 measured with an accuracy of O.OOlmra and its range is up to 10mm. The second model is more economical than the first model because of the reduced quantities of mercury. Also there is a slight improvement in the measurement accuracy of AH. In this model too air can be used as an experimental fluid (Y=/a) instead of water and in such a case the following governing equation, similar to Eq.5 is derived from Eq.3. AH = AZ2 [(l+a/A)(Y„ -Ya)/Yw -K2a/A)(yw -Ya)/Yw] (5a) Illustration of Third Model: Modcl-3A and 3B: This is a very interesting model because the mercury is totally avoided in all the sumps. It contains only water and air, and one can consider it as an inverted air manometer. however with a difference that a metallic float is used in Sump 82- The probe M and the metallic float forms a capacitance in which M is a fixed plate where as the float is a movable plate and its movement is due to the pressure changes m the system. Thus in this model, Ymi = yra2 = y = Vw and substituting them in Eq. 3, the governing equation for the third model, for water as the experimental fluid, is obtained as follows. AH = AZ2 [{l+a/A){l VYW)] (6) By taking the usual values of a/A = 0.1 and ya/y* ^ 1.02x10 ^ the manometer constant. CM = 1.1. Hence the sensitivity of the instrument is 0.0011 mm of water head (because, like in all the models, AZ2 is measured with an accuracy of O.OOI mm.). Even though it has remarkably a very high accuracy but the range of AH is limited only to 11mm of water head because the maximum range of AZ2 is only 10mm. It is of importance to note that, in this model while using water as the experimental fluid, cross-sectional areas of the sumps S\ and S4 have no consequence (as they are filled completely with water); however, cross sectional areas of the sumps, S2 and S3 can effect significantly the accuracy and range of AH measurement. Also, on many times a higher range of AH is desirable at the expense of a lower accuracy. This can be achieved by increasing the value of a/A i.e., the ratio of cross-sectional areas of sumps S2 and S3 such that a»A (It may be noted that A»a in the previous models). For an example, if a/A =10, the manometer constant CM becomes 11 and thus the accuracy of measurement of AH is now reduced to 0.011mm and its range is increased to 110mm of water head. This model is the most economical when compared to all other models because mercury is totally avoided. However, pressure fluctuations are relatively more in this model and some special techniques have to be adopted in the manometer-circuit to suppress such fluctuations. In this model too air can be used as the experimental fluid instead of water. Hence by making use of the conditions ymi = ym2 = yw! y = ya and as usual A| = A3 = A4 = A and A2 = a in Eq. 3, the following equation can be obtained for air as the experimental fluid for the third model. AH = AZ2 [(l+3a/A)(l -yAw)] (6a) We Claim: 1. A Digital Micro Manometer comprising: (a) a manometer circuit consisting of four interconnected cylindrical sumps Si, S2, S3 and S4 for holding experimental fluids through which differential pressures arc applied: the said sumps are being provided with suitable means to induct sufficient quantities of manometric fluids: a probe M is provided at the top of sump S^^ for measuring the air gap between the mercury meniscus and itself; and (b) a capacitive transducer means to measure accurately and display digitally the air gap AR in terms of AZj, from which the differential head, AH is determined. 2. A Digital Micro Manometer of claim 1, wherein the suitable means to induct sufficient quantities of manometnc fluids are cocks (CI, C2, C3). 3. The Digital Micro Manometer as claimed in claim 1, whcrcm the fluids used are air, water or any other suitable liquid. 4. The Digital Micro Manometer as claimed in claim I and 3, wherein the said sumps have uniform cross-scctional areas A|, A2, A^and A4, 5. The Digital Micro Manometer as claimed in any one of clauns 1 to 4, wherein the capacitive transducer means comprises of an input means including signal input to input the capacitance to a detector circuit with a fixed capacitor so as to detect the difference in capacitance, the output of the detector circuit being fed to an AC-DC converter circuit and a filler amplifier to obtam a stable DC output, a second known input means to feed the DC voltage to a digital display which displays the distance between the transducer and mercurj' meniscus directly m mm. 6. The Digital Micro Manometer as claimed in claim 5, wherem the signal output is connected to a recorder, oscilloscope or a data acquisition s\stem.

Documents:

0052-che-2004 abstract duplicate.pdf

0052-che-2004 abstract.pdf

0052-che-2004 claims duplicate.pdf

0052-che-2004 claims.pdf

0052-che-2004 correspondence-others.pdf

0052-che-2004 correspondence-po.pdf

0052-che-2004 description (complete) duplicate.pdf

0052-che-2004 description (complete).pdf

0052-che-2004 drawings duplicate.pdf

0052-che-2004 drawings.pdf

0052-che-2004 form-1.pdf

0052-che-2004 form-18.pdf

0052-che-2004 form-26.pdf

0052-che-2004 form-5.pdf