the end of experiment the student should be able to: Identify the dierent dierent parts of of weighing scale scale and ow meter. meter. Use the platform platform balance and know know how to read read olume ow meter meter.. !now !now how to to calibr calibrate ate weighi weighing ng scale. scale.
DISCUSSION OF THEORY
"#A$U%#"#&' ( *#I+,' A&- (/U"# *eighing eighing is a primary primary method method of measuri measuring ng forces0 forces0 and olumetric olumetric dei deice ces s are are cali calibr brat ated ed init initia iall lly y by dir direct ect we weig ighi hing ng.. $cal $cales es hae hae been been constructed to weigh a million pounds or more 1testing) machines0 while the chemical balance0 at the opposite extreme0 will easily weigh a millionth of a pound. Platform Scale 2latf 2latfor orm m scale scale is an indu industr strial ial weigh weighing ing instr instrume ument nt consi consisti sting ng of a platform coupled to an automatic system of leers and ad3ustable weights0 used to weigh large or heay ob3ects. 'he common platform platform scale used in the laboratory laboratory consists of a compound leerage system such as the one shown. A series of standard weigh weights ts hung hung on one one end end of the leera leerage ge syste system m sere seres s to balan balance ce an unknown weight at the other end of the system. !nife4edge fulcrums are ordinarily used0 although torsion bands or exure plates are introduced in large scales to eliminate friction. 'he latter construction allows accuracy as great as 5 part in a million.
Triple Beam Balance 'he 'riple 'riple 6eam 6alance 6alance is a typical mechanical mechanical balance. balance. It has a beam beam which is supported by a fulcrum. (n one side is a pan on which the ob3ect is placed. (n the other side0 the beam is split into three parallel beams0 each supporting one weight. In measuring the weight of an ob3ect0 rather than
adding additional weights0 each of the three weights can be slid along the beam to increase their leer arm.
Flow Measurement in History (ur interest in the measurement of air and water ow is timeless. !nowledge of the direction and elocity of air ow was essential information for all ancient naigators0 and the ability to measure water ow was necessary for the fair distribution of water through the a7ueducts of such early communities as the $umerian cities of Ur0 !ish0 and "ari near the 'igris and #uphrates %iers around 80999 6.. Terminology 'he term ow measurement is a general term0 and before selecting a ow meter it is important to be sure what type of ow measurement is actually re7uired. or a uid owing through a pipe0 ow measurement may mean any of six dierent types of measurement.
5. 2oint elocity measurement4 the uid;s elocity at a . "ean ow elocity measurement4 aerage uid elocity across the cross section of the pipe 1m=s) ?. olumetric ow rate measurement4 the rate of change in the olume of uid passing through the pipe with time 1m ?=s) @. 'otal olume measurement4 the total olume of uid which has passed through the pipe 1m ?) 8. "ass ow rate measurement4 the rate of change in the mass of the uid passing through the pipe with time 1kg=s) . 'otal mass measurement4 the total mass of uid passing through the pipe 1kg=s)
Although the most common type of ow measurement is that of a uid through a closed conduit or pipe0 open channel ow measurements are also regularly needed in applications such as sewage and water treatment. What is a Flow Meter? A deice that measures the ow rate i.e. the 7uantity of a uid owing in unit time in an open or closed conduit. low meter is identi
'he ob3ect of installing a ow meter is to obtain a measure of the ow rate0 usually in the form of an electrical signal0 which is ambiguous and with a speci
Volume Tanks 'anks are used for the collection of uid that has passed through a ow meter being calibrated and can be used to dispense li7uid through a ow meter for calibration. 'he dierential pressure 1-2) between two points or leels in a li7uid depends on the density 1C)0 the acceleration due to graity 1g)0 and the ertical separation between the two points or leels. 'herefore0 in a simple system0 if one could determine the -2 between the bottom of a tank containing li7uid and the surface of the li7uid0 the height of the li7uid could be inferred from C and g. If the mean cross4sectional area of the tank were known or could be inferred0 the olume of the li7uid in the tank could be determined. hanges in the height 1and therefore olume) of the li7uid could be determined from -2 measurements before and after collection or discharge of li7uid.
III.
SET-UP
IV.
APPARATUS
5. >. ?. @. 8. . V.
2latform scale 1set of counter weights) $teel tape alibrated tank *ater meter 'riple beam balance 'hermometer
omputations: Aerage: E .>8 kg Aerage F 1.?9 G .?9 G .?9 G .?9 G .58)=8 F .>D kg E .89 kg AerageF 1.89 G .89 G .89 G .89 G .89)=8 F .89 kg E 5.99 kg Aerage F 15.99 G 5.99 G 5.99 G 5.99 G 5.99)=8 F 5.99 kg E 5.89 kg Aerage F 15.89 G 5.89 G 5.89 G 5.89 G 5.89)=8 F 5.89 kg 6) $ensitiity of 2latform $cale 'rial 5. 2aper >. #raser ?. %ing @. +uitar pick 8. 'issue
/oad 1grams) 5.D 9.@ 5.H 5.?8 9.?
'rial . 2en cap D. lash -rie H. andy wrapper . 'ooth pick 59. 6all chain
) alibration of water meter and olume tank
/oad 1grams) ?.9 5.8 9.58 9.58 5.59
'rial s
Initial reading of water meter
inal readin g of water meter
5
DD.@5 > DD.D> DD.H9 ?
DD.D> DD.H9 ? DD.? 9
> ?
olume based on water meter 1m?)
$cale olum readin e g 1kg) based on mass 1m?) 9.8 8H.@ 88
ross section al Area of tank 1m>)
. ?9>8 . ?9>8 . ?9>8
,eig olum ht of e wate 6ased r 1m) on water leel 1m?) 9.9 9.98 8 9.9@
VI. OBSERVATION VII. CONCLUSION VIII. RESEARCH QUESTIONS
5. -iscuss how heay loads like ten wheeler trucks are weigh. 'rucks are weighed by driing them onto metal roadways called weighbridges0 which are supported by hydraulic rams. 'he heaier the truck0 the greater the force on the rams and the harder they hae to push upward to balance the truckJs weight exactly. Kou can calculate the truckJs weight from the hydraulic pressure of the rams. If you know the truckJs curb weight 1kerb weight or unladen weight)0 which is often painted on the side of the ehicle0 you can easily calculate the weight of its cargo by subtraction. >. *hat are the sources of error in weighingL a. %eading the weight from dierent angles b. hange in temperature c. &on4leel surface under weighing machine or scale d. Additional weight of some unwanted things like dust or absorbed moisture e. Internal fault f. Incorrectly ad3usted balance g. Inuence of the operator 1parallax errors when reading a display that has a pointer0 change in the mass of an ob3ect being weighed when the operator touches it with his or her hands) h. luctuations in the displayed weight0 for instance0 caused by wind. i. A balance with incorrectly ad3usted sensitiity
?. *ith the aid of drawing discuss the operation of the following instruments used to measure olumetric ow: a. %otary disk meter (2#%A'I(& 2%I&I2/#
'he motion of the disk is guided by two half balls mounted upon it0 and with each complete reolution a
It measures the gas ow by trapping it between two impellers that rotate in opposite directions. 'he bottom impeller turns counterclockwise0 allowing the gas to enter the space between the
impeller and the casing. As the impeller reaches the horiBontal position the measured 7uantity of gas is contained between the impeller and case wall. 'he gas discharges through to the outlet0 as the impeller continues to turn. c. %eoling drum condensate meter (2#%A'I(& 2%I&I2/#
'he drum consists of six scroll4shaped sections. /i7uid enters the drum through an axially mounted inlet lowing "eter spout at the center of the meter. As each section
/i7uid enters into a precision machined chamber which contains an oscillating piston. 'he position of the piston diides the chamber into compartments containing an exact olume. 'he li7uid pressure causes the piston to oscillate and rotate its centre hub. 'he moements of the hub are sensed through the meter wall by a series of magnets. #ach reolution of the piston hub is e7uialent to a
minimum slippage of the li7uid for highly accurate and repeatable measurement of each olume cycle. d.>) %eciprocating 2iston "eter 2%I&I2/# ( (2#%A'I(&
$uppose the piston is at the bottom of its stroke. 'he ale is so arranged that inlet li7uid is admitted below the piston0 causing it to trael upward and the li7uid aboe the piston to be discharged to the outlet pipe. *hen the piston has reached the limits of its trael0 the top of the cylinder is cut o from the outlet side and opened to the inlet li7uid supply. At the same time the bottom of the cylinder is opened to the outlet side but cut o from the inlet li7uid. 'he pressure of the incoming li7uid will therefore drie the piston downward0 discharging the li7uid from below the piston to the outlet pipe. 'he process repeats. As the piston reciprocates0 a ratchet attached to the piston rod proides an actuating force for an incremental counter0 each count representing a predetermined 7uantity of li7uid. e. 6ellow +as meter (2#%A'I(& 2%I&I2/#
6ellows gas meters measure the 7uantity of gas passing through them by
'hus the alue of coeNcient of discharge aries with the alues of and . An aerage of coeNcient of discharge aries from 9.9 to 9.@. b. oeNcient of elocity 'he ratio of actual elocity of the 3et0 at ena4contracta0 to the theoretical elocity is known as coecient of !elocity . 'he theoretical elocity of 3et at ena4contracta is gien by the relation0 0 where h is the head of water at ena4contracta. "athematically coeNcient of elocity0
'he dierence between the elocities is due to friction of the ori
'he alue of oeNcient of contraction aries slightly with the aailable head of the li7uid0 siBe and shape of the ori
uel gauge -" has three4dimension ring type measuring chamber. -O generates an impulse0 when the olume of fuel 1which is e7ual to olume of the measuring chamber) passes through it.
