MACAM-MACAM JENIS TIMBANGAN DAN PENGGUNAANNYA.
Timbangan Pocket
Jenis timbangan kecil yang bisa dibawa kemana mana.
Disamping dimensinya kecil juga kapasitas yang disandangnya pun
kecil. Biasanya dengan kapasitas 30 kg kebawah.
Timbangan Portable/ Bench Scale
Timbangan ini terpisah antara tempat timbang dan
penunjukannya ( Indicator ). Biasanya
dihubungkan dengan tiang penyangga.
Kalau dari Pabrikan resmi biasanya ukurannya
sudah tertentu semisal : 30 x 40 cm, 45 x 60 cm
dll.
Sebagian pabrikan timbangan baik dari China,
Jepang, Korea, Eropa dan Amerika mengeluarkan
produk ini. Semisal Cardinal dari Amerika, Avery
dari Eropa mengeluarkan Seri HL nya, Kemudian
Shimadzu dari JEPANG dan UWE buatan
Taiwan.
Ukuran kapasitas timbangan ini biasanya antara
lain : 6 kg, 15 kg, 30 kg, 60 kg, 100 kg, sampai
300 kg. Timbangan model ini juga bisa dibuat
sesuai pesanan sipembeli sendiri dari mulai
ukuran maupun kapasitasnya.
Timbangan Platform/ Floor Scales
Timbangan ini seperti bench scale. Yang
membedakan adalah Kapasitasnya lebih besar
tidak adanya tiang penyangga. Dimensi tempat
timbangpun akan jauh lebih besar.
Biasanya Platform dari floor scale dibuat oleh
pabrikan lokal untuk menekan biaya produksinya.
Disini floor scale akan benar benar membebaskan penggunanya untuk menentukan
ukuran Platform yang cocok. Ukuran yang biasa
dipesan adalah 1 x 1m, 1,2 x 1 m, 1,2 x 1,2 m, 1,5
x 1,5 m dll.
Dinamakan timbangan lantai awal mulanya karena
timbangan ini biasanya ditanam dilantai yang
dibuat kolam, jadinya timbangan tersebut akan
rata dengan lantai.
Biasanya barang yang akan ditimbang di foor
Scale ini adalah barang dengan beban berat.
Barang tersebut dibawa dengan memakai kereta
dorong. Jadi disitu karena timbangan rata dengan
lantai maka kereta tinggal disorong ketempat
timbang kemudian barang ditaruh ditimbang dan
kereta keluar. Timbangan tersebut bisa dibuat
dengan memenuhi permintaan pesanan dari
sipemakai.
Timbangan Gantung/ Crane Scale/ Hanging Scale
Dinamakan timbangan gantung karena system
penimbangannya digantungkan ditimbangan
tersebut.
Jadi Timbangan tersebut tidak mempunyai
platform tempat timbang.
Beban yang akan ditimbang digantung langsung
menarik Loadcell yang sudah menyatu dengan
Indicatornya.
Timbangan Ternak (Live Stock/ Animal Weighing)
Dinamakan timbangan ternak karena kegunaan
timbangan ini untuk menimbang hewan ternak
semisal sapi, kerbau, kambing dll.
Perbedaan timbangan ternak elektronik dengan
timbangan elektronik lain adalah adanya fungsi
HOLD / PEAK HOLD disamping memang tempat
timbangnya yang juga berbeda.
Fungsi HOLD adalah fungsi dimana bila didapat
angka yang sering menunjuk maka angka tersebut
otomatis berhenti dan mengunci.
Sedang fungsi PEAK HOLD adalah sama dengan
HOLD akan tetapi angka berhentinya pada saat
timbangan mendapatkan angka tertingginya.
Fungsi-fungsi ini diterapkan pada timbangan
ternak karena bila hewan ternak ditimbang pasti
akan bergerak-gerak terus. Bergeraknya benda
diatas timbangan akan menyebabkan angka tidak
bisa stabil.
Timbangan Tahan Air (Waterproof)
Seperti timbangan-timbangan elektronik yang
lainnya. Timbangan waterproof memiliki
kelebihan akan adanya ketahanan terhadap
lingkungan yang berair dan lembab.
Timbangan ini biasanya dipakai untuk Industri
Ikan atau hewan yang hidup diair. Lingkungan
yang dingin, lembab dan cenderung basah akan
mengakibatkan timbangan biasa tidak bisa
bertahan.
Pada produk timbangan waterproof tertentu malah
ada yang mengklaim bisa tahan tidak rusak
walaupun direndam dalam air sekalipun.
Timbangan Penghitung Satuan (Counting Scale)
Timbangan ini berfungsi untuk menghitung
barang barang kecil yang bila dilakukan akan memakan waktu. Semisal Baut dan Mur, Kancing,
Tablet obat dll.
Kerja timbangan ini adalah dengan
menimbangkan sample dulu ketimbangan.
Semisal 10 biji kancing. Selanjutnya berat kancing
itu akan disimpan didalam memori timbangan itu
untuk jumlah 10 kancing. Setelah itu berapapun
kancing yang dimasukan kedalam timbangan akan
bisa dihitung berat dan jumlahnya oleh timbangan
tersebut.
Timbangan Harga Retail ( Retail Computing Scale )
Timbangan ini biasanya dipakai untuk menimbang
buah, oleh-oleh, makanan kecil, permen, daging dll.
Biasanya dipakai oleh Toko Buah, Oleh-oleh,
Supermarket, Minimarket dll.
Timbangan tersebut dilengkapi dengan 3 buah display
antara lain : display untuk penunjukan berat, display
untuk harga perkilo barang yang ditimbang dan display
untuk total harga.
Timbangan jenis ini juga ada yang memiliki berbagai
fitur yang lengkap. Antara lain :
Memiliki memory yang besar hingga bisa menyimpan
PLU sampai 3000. Itu artinya timbangan tersebut bisa
memuat data barang dan harganya sampai 3000 item.
Bisa Melakukan Berbagai Jurnal dan Laporan. Barang-
barang yang sudah laku, nama maupun jumlahnya bisa
dibuatkan jurnalnya setiap saat.
Dilengkapi dengan printer yang akan mencetak dari
setiap transaksi yang ada.
Ada Interface yang bisa mengkomunikasi timbangan
tersebut dengan timbangan-timbangan sejenis yang
lain kemudian semuanya bermuara ke komputer Induk.
Jaringan tersebut nanti berbentuk LAN.
Timbangan Laboratorium (Lab. Balance)
Timbangan ini dipakai dilaboratorium. Biasanya
dengan ketelitian yang cukup tinggi. Range yang
dipakai antara 0,01 g sampai 0,0001 g.
Timbangan Kadar Air (Moisture Balance)
Timbangan tersebut sangatlah unik yaitu bisa
mengeluarkan panas.
Jadi kegunaan timbangan tersebut adalah untuk
mengetahui seberapa banyak kadar air yang
tersembunyi dalam setiap barang yang ditest.
Cara kerja timbangan tersebut adalah sebagai
berikut : Barang yang akan ditest kadar airnya
ditimbang terlebih dahulu. Setelah didapat
beratnya kemudian barang tersebut dipanaskan
oleh system pemanas dari timbangan. Setelah
dipanasi kemudian barang tersebut ditimbang lagi.
Perbandingan antara berat barang yang basah /
belum dipanasi dengan barang yang sudah kering
setelah dipanasi itulah yang menjdi pengukuran
kadar airnya
Timbangan Mobil & Truk
(Truck Scele/ Weighbridge/ Jembatan Timbang)
Inilah Jenis timbangan paling besar. Dinamakan
jembatan timbang karena memang bentuknya
seperti jembatan. Timbangan ini dipergunakan
untuk menimbang kendaraan roda 4 atau lebih.
Kapasitas timbangan ini bisa sampai 100 ton
dengan dimensi yang berbeda-beda. Ada ukuran 9
x 3 m, 12 x 3 atau 16 x 3 m.
Jembatan Timbang sekarang sudah bukan
monopoli milik LLAJR saja melainkan sudah
merupakan kebutuhan pokok perusahaan-
perusahaan yang mempunyai kegiatan bongkar
muat barang dengan kendaraan bermotor.
Sumber : http://alat2xukur.wordpress.com/2011/01/04/macam-macam-jenis-timbangan-dan-
penggunaannya/ ( diunduh pada tanggal 12 oktober 2013 pada pukul 12.15 wib).
pH METER
A pH meter is an electronic device used for measuring the pH (acidity or alkalinity) of a liquid
(though special probes are sometimes used to measure the pH of semi-solid substances). A typical
pH meter consists of a special measuring probe (a glass electrode) connected to an electronic meter
that measures and displays the pH reading.
The probe
The probe is an essential part of a pH meter, it is a rod like structure usually made up of glass.
At the bottom of the probe there is a bulb, the bulb is a sensitive part of a probe that contains
the sensor. Never touch the bulb by hand and clean it with the help of an absorbent tissue
paper with very soft hands, being careful not to rub the tissue against the glass bulb in order
to avoid creating static. To measure the pH of a solution, the probe is dipped into the solution.
The probe is fitted in an arm known as the probe arm.
Calibration and use
For very precise work the pH meter should be calibrated before each measurement. For
normal use calibration should be performed at the beginning of each day. The reason for this
is that the glass electrode does not give a reproducible e.m.f. over longer periods of time.
Calibration should be performed with at least two standard buffer solutions that span the
range of pH values to be measured. For general purposes buffers at pH 4.01 and pH 10.00 are
acceptable. The pH meter has one control (calibrate) to set the meter reading equal to the
value of the first standard buffer and a second control (slope) which is used to adjust the
meter reading to the value of the second buffer. A third control allows the temperature to be
set. Standard buffer sachets, which can be obtained from a variety of suppliers, usually state
how the buffer value changes with temperature. For more precise measurements, a three
buffer solution calibration is preferred. As pH 7 is essentially, a "zero point" calibration (akin
to zeroing or taring a scale or balance), calibrating at pH 7 first, calibrating at the pH closest
to the point of interest (e.g. either 4 or 10) second and checking the third point will provide a
more linear accuracy to what is essentially a non-linear problem. Some meters will allow a
three point calibration and that is the preferred scheme for the most accurate work. Higher
quality meters will have a provision to account for temperature coefficient correction, and
high-end pH probes have temperature probes built in. The calibration process correlates the
voltage produced by the probe (approximately 0.06 volts per pH unit) with the pH scale.
After each single measurement, the probe is rinsed with distilled water or deionized water to
remove any traces of the solution being measured, blotted with a scientific wipe to absorb any
remaining water which could dilute the sample and thus alter the reading, and then quickly
immersed in another solution.
Storage conditions of the glass probes
When not in use, the glass probe tip must be kept wet at all times to avoid the pH sensing
membrane dehydration and the subsequent dysfunction of the electrode.
A glass electrode alone without combined reference electrode is typically stored immersed in
an acidic solution of around pH 3.0. In an emergency, acidified tap water can be used, but
distilled or deionised water must never be used for longer-term probe storage as the relatively
ionless water "sucks" ions out of the probe membrane through diffusion, which degrades it.
Combined electrodes (glass membrane + reference electrode) are better stored immersed in
the bridge electrolyte (often KCl 3 M) to avoid the diffusion of the electrolyte (KCl) out of
the liquid junction.
Cleaning and troubleshooting of the glass probes
Occasionally (about once a month), the probe may be cleaned using pH-electrode cleaning
solution; generally a 0.1 M solution of hydrochloric acid (HCl) is used, having a pH of one.
Alternatively a dilute solution of ammonium fluoride (NH4F) can be used. To avoid
unexpected problems, the best practice is however to always refer to the electrode
manufacturer recommendations or to a classical textbook of analytical chemistry.
Types of pH meters
pH meters range from simple and inexpensive pen-like devices to complex and expensive
laboratory instruments with computer interfaces and several inputs for indicator and
temperature measurements to be entered to adjust for the slight variation in pH caused by
temperature. Specialty meters and probes are available for use in special applications, harsh
environments, etc.
History
The first commercial pH meters were built around 1936 by Radiometer in Denmark and by
Arnold Orville Beckman in the United States. While Beckman was an assistant professor of
chemistry at the California Institute of Technology, he was asked to devise a quick and
accurate method for measuring the acidity of lemon juice for the California Fruit Growers
Exchange (Sunkist). Beckman's invention helped him to launch the Beckman Instruments
company (now Beckman Coulter). In 2004 the Beckman pH meter was designated an ACS
National Historic Chemical Landmark in recognition of its significance as the first
commercially successful electronic pH meter.
In the 1970s Jenco Electronics of Taiwan designed and manufactured the first portable digital
pH meter. This meter was sold under Cole-Parmer's label.
Building a pH meter
Because the circuitry of a basic pH meter is quite simple, it is possible to build a serviceable
pH meter or pH controller with parts available at a neighborhood electronics retailer. (pH
probes, however, are not so easily acquired and must usually be ordered from a scientific
instrument supplier.) For a walkthrough of how to build the simplest possible pH meter or a
detailed description of how to build a pH meter/pH controller, see The pH Pages. The
application note for the LM6001 chip at the National Semiconductor web site also has a very
simple demonstration circuit. Although the application note is for a specialty IC, serviceable
pH meters can be built from any operational amplifier with a high input impedance, such as
the common and inexpensive National Semiconductor TL082 or its equivalent.
Sumber : http://en.wikipedia.org/wiki/PH_meter,( diunduh pada tanggal 12 oktober 2013 pada
pukul 12.15 wib).
Viscometer
A viscometer (also called viscosimeter) is an instrument used to measure the viscosity of a fluid. For
liquids with viscosities which vary with flow conditions, an instrument called a rheometer is used.
Viscometers only measure under one flow condition.
In general, either the fluid remains stationary and an object moves through it, or the object is
stationary and the fluid moves past it. The drag caused by relative motion of the fluid and a surface is
a measure of the viscosity. The flow conditions must have a sufficiently small value of Reynolds
number for there to be laminar flow.
At 20.00 degrees Celsius the viscosity of water is 1.002 mPas and its kinematic viscosity (ratio of
viscosity to density) is 1.0038 mm2/s. These values are used for calibrating certain types of
viscometer.
Standard laboratory viscometers for liquids
U-tube viscometers
These devices also are known as glass capillary viscometers or Ostwald viscometers, named
after Wilhelm Ostwald. Another version is the Ubbelohde viscometer, which consists of a U-
shaped glass tube held vertically in a controlled temperature bath. In one arm of the U is a
vertical section of precise narrow bore (the capillary). Above this is a bulb, with it is another
bulb lower down on the other arm. In use, liquid is drawn into the upper bulb by suction, then
allowed to flow down through the capillary into the lower bulb. Two marks (one above and
one below the upper bulb) indicate a known volume. The time taken for the level of the liquid
to pass between these marks is proportional to the kinematic viscosity. Most commercial
units are provided with a conversion factor, or can be calibrated by a fluid of known
properties. The time required for the test liquid to flow through a capillary of a known
diameter of a certain factor between two marked points is measured. By multiplying the time
taken by the factor of the viscometer, the kinematic viscosity is obtained.
Such viscometers are also classified as direct flow or reverse flow. Reverse flow viscometers
have the reservoir above the markings and direct flow are those with the reservoir below the
markings. Such classifications exists so that the level can be determined even when opaque or
staining liquids are measured, otherwise the liquid will cover the markings and make it
impossible to gauge the time the level passes the mark. This also allows the viscometer to
have more than 1 set of marks to allow for an immediate timing of the time it takes to reach
the 3rd mark, therefore yielding 2 timings and allowing for subsequent calculation of
Determinability to ensure accurate results.
Falling sphere viscometers
Stokes' law is the basis of the falling sphere viscometer, in which the fluid is stationary in a
vertical glass tube. A sphere of known size and density is allowed to descend through the
liquid. If correctly selected, it reaches terminal velocity, which can be measured by the time it
takes to pass two marks on the tube. Electronic sensing can be used for opaque fluids.
Knowing the terminal velocity, the size and density of the sphere, and the density of the
liquid, Stokes' law can be used to calculate the viscosity of the fluid. A series of steel ball
bearings of different diameter are normally used in the classic experiment to improve the
accuracy of the calculation. The school experiment uses glycerine as the fluid, and the
technique is used industrially to check the viscosity of fluids used in processes. It includes
many different oils, and polymer liquids such as solutions.
In 1851, George Gabriel Stokes derived an expression for the frictional force (also called
drag force) exerted on spherical objects with very small Reynolds numbers (e.g., very small
particles) in a continuous viscous fluid by changing the small fluid-mass limit of the
generally unsolvable Navier-Stokes equations:
where:
is the frictional force, is the radius of the spherical object, is the fluid viscosity, and is the particle's velocity.
If the particles are falling in the viscous fluid by their own weight, then a terminal velocity,
also known as the settling velocity, is reached when this frictional force combined with the
buoyant force exactly balance the gravitational force. The resulting settling velocity (or
terminal velocity) is given by:
where:
Vs is the particles' settling velocity (m/s) (vertically downwards if ,
upwards if ), is the Stokes radius of the particle (m), g is the gravitational acceleration (m/s2), p is the density of the particles (kg/m
3), f is the density of the fluid (kg/m
3), and is the (dynamic) fluid viscosity (Pa s).
Note that Stokes flow is assumed, so the Reynolds number must be small.
A limiting factor on the validity of this result is the roughness of the sphere being used.
A modification of the straight falling sphere viscometer is a rolling ball viscometer which
times a ball rolling down a slope whilst immersed in the test fluid. This can be further
improved by using a patented V plate which increases the number of rotations to distance
traveled, allowing smaller more portable devices. This type of device is also suitable for ship
board use.
Falling Piston Viscometer
Also known as the Norcross viscometer after its inventor, Austin Norcross. The principle of
viscosity measurement in this rugged and sensitive industrial device is based on a piston and
cylinder assembly. The piston is periodically raised by an air lifting mechanism, drawing the
material being measured down through the clearance (gap) between the piston and the wall of
the cylinder into the space which is formed below the piston as it is raised. The assembly is
then typically held up for a few seconds, then allowed to fall by gravity, expelling the sample
out through the same path that it entered, creating a shearing effect on the measured liquid,
which makes this viscometer particularly sensitive and good for measuring certain thixotropic
liquids. The time of fall is a measure of viscosity, with the clearance between the piston and
inside of the cylinder forming the measuring orifice. The viscosity controller measures the
time of fall (time-of-fall seconds being the measure of viscosity) and displays the resulting
viscosity value. The controller can calibrate the time-of-fall value to cup seconds (known as
efflux cup), Saybolt universal second (SUS) or centipoise.
Industrial use is popular due to simplicity, repeatability, low maintenance and longevity. This
type of measurement is not affected by flow rate or external vibrations. The principle of
operation can be adapted for many different conditions, making it ideal for process control
environments.
Oscillating Piston Viscometer
Sometimes referred to as electromagnetic viscometer or EMV viscometer, was invented at
Cambridge Viscosity (Formally Cambridge Applied Systems) in 1986. The sensor (see figure
below) comprises a measurement chamber and magnetically influenced piston.
Measurements are taken whereby a sample is first introduced into the thermally controlled
measurement chamber where the piston resides. Electronics drive the piston into oscillatory
motion within the measurement chamber with a controlled magnetic field. A shear stress is
imposed on the liquid (or gas) due to the piston travel and the viscosity is determined by
measuring the travel time of the piston. The construction parameters for the annular spacing
between the piston and measurement chamber, the strength of the electromagnetic field, and
the travel distance of the piston are used to calculate the viscosity according to Newtons Law of Viscosity.
The oscillating piston viscometer technology has been adapted for small sample viscosity and
micro-sample viscosity testing in laboratory applications. It has also been adapted to measure
high pressure viscosity and high temperature viscosity measurements in both laboratory and
process environments. The viscosity sensors have been scaled for a wide range of industrial
applications such as small size viscometers for use in compressors and engines, flow-through
viscometers for dip coating processes, in-line viscometers for use in refineries, and hundreds
of other applications. Improvements in sensitivity from modern electronics, is stimulating a
growth in oscillating piston viscometer popularity with academic laboratories exploring gas
viscosity.
Vibrational viscometers
Vibrational viscometers date back to the 1950s Bendix instrument, which is of a class that
operates by measuring the damping of an oscillating electromechanical resonator immersed
in a fluid whose viscosity is to be determined. The resonator generally oscillates in torsion or
transversely (as a cantilever beam or tuning fork). The higher the viscosity, the larger the
damping imposed on the resonator. The resonator's damping may be measured by one of
several methods:
1. Measuring the power input necessary to keep the oscillator vibrating at a constant amplitude. The higher the viscosity, the more power is needed to maintain the amplitude of oscillation.
2. Measuring the decay time of the oscillation once the excitation is switched off. The higher the viscosity, the faster the signal decays.
3. Measuring the frequency of the resonator as a function of phase angle between excitation and response waveforms. The higher the viscosity, the larger the frequency change for a given phase change.
The vibrational instrument also suffers from a lack of a defined shear field, which makes it
unsuited to measuring the viscosity of a fluid whose flow behaviour is not known before
hand.
Vibrating viscometers are rugged industrial systems used to measure viscosity in the process
condition. The active part of the sensor is a vibrating rod. The vibration amplitude varies
according to the viscosity of the fluid in which the rod is immersed. These viscosity meters
are suitable for measuring clogging fluid and high-viscosity fluids, including those with
fibers (up to 1,000 Pas). Currently, many industries around the world consider these
viscometers to be the most efficient system with which to measure the viscosities of a wide
range of fluids; by contrast, rotational viscometers require more maintenance, are unable to
measure clogging fluid, and require frequent calibration after intensive use. Vibrating
viscometers have no moving parts, no weak parts and the sensitive part is very small. Even
very basic or acidic fluids can be measured by adding a protective coating such as enamel, or
by changing the material of the sensor to a material such as 316L stainless steel.
Rotational viscometers
Rotational viscometers use the idea that the torque required to turn an object in a fluid is a
function of the viscosity of that fluid. They measure the torque required to rotate a disk or
bob in a fluid at a known speed.
'Cup and bob' viscometers work by defining the exact volume of a sample which is to be
sheared within a test cell; the torque required to achieve a certain rotational speed is
measured and plotted. There are two classical geometries in "cup and bob" viscometers,
known as either the "Couette" or "Searle" systems - distinguished by whether the cup or bob
rotates. The rotating cup is preferred in some cases because it reduces the onset of Taylor
vortices, but is more difficult to measure accurately.
'Cone and Plate' viscometers use a cone of very shallow angle in bare contact with a flat
plate. With this system the shear rate beneath the plate is constant to a modest degree of
precision and deconvolution of a flow curve; a graph of shear stress (torque) against shear
rate (angular velocity) yields the viscosity in a straightforward manner.
Electromagnetically Spinning Sphere Viscometer (EMS Viscometer)
The EMS Viscometer measures the viscosity of liquids through observation of the rotation of
a sphere which is driven by electromagnetic interaction: Two magnets attached to a rotor
create a rotating magnetic field. The sample to be measured is in a small test tube . Inside the
tube is an aluminium sphere . The tube is located in a temperature controlled chamber and
set such that the sphere is situated in the centre of the two magnets. The rotating magnetic
field induces eddy currents in the sphere. The resulting Lorentz interaction between the
magnetic field and these eddy currents generate torque that rotates the sphere. The rotational
speed of the sphere depends on the rotational velocity of the magnetic field, the magnitude of
the magnetic field and the viscosity of the sample around the sphere. The motion of the
sphere is monitored by a video camera located below the cell. The torque applied to the
sphere is proportional to the difference in the angular velocity of the magnetic field B and the one of the sphere S. There is thus a linear relationship between (BS)/S and the viscosity of the liquid.
This new measuring principle was developed by Sakai et al. at the University of Tokyo. The
EMS viscometer distinguishes itself from other rotational viscometers by three main
characteristics:
All parts of the viscometer which come in direct contact with the sample are disposable and inexpensive.
The measurements are performed in a sealed sample vessel. The EMS Viscometer requires only very small sample quantities (0.3 mL).
Stabinger viscometer
Stabinger Viscometer principle
By modifying the classic Couette type rotational viscometer, it is possible to combine the
accuracy of kinematic viscosity determination with a wide measuring range.
The outer cylinder of the Stabinger Viscometer is a tube that rotates at constant speed in a
temperature-controlled copper housing. The hollow internal cylinder shaped as a conical rotor is specifically lighter than the filled samples and therefore floats freely within them, centered by centrifugal forces. In this way all bearing friction, an inevitable factor in most
rotational devices, is fully avoided. The rotating fluid's shear forces drive the rotor, while a
magnet inside the rotor forms an eddy current brake with the surrounding copper housing. An
equilibrium rotor speed is established between driving and retarding forces, which is an
unambiguous measure of the dynamic viscosity. The speed and torque measurement is
implemented without direct contact by a Hall effect sensor counting the frequency of the
rotating magnetic field. This allows for a highly precise torque resolution of 50 pNm and a
wide measuring range from 0.2 to 20,000 mPas with a single measuring system. A built-in density measurement based on the oscillating U-tube principle allows the determination of
kinematic viscosity from the measured dynamic viscosity employing the relation
where:
is the kinematic viscosity (mm2/s) is the dynamic viscosity (mPa.s) is the density (g/cm3)
Bubble viscometer
Bubble viscometers are used to quickly determine kinematic viscosity of known liquids such
as resins and varnishes. The time required for an air bubble to rise is directly proportional to
the viscosity of the liquid, so the faster the bubble rises, the lower the viscosity. The
Alphabetical Comparison Method uses 4 sets of lettered reference tubes, A5 through Z10, of
known viscosity to cover a viscosity range from 0.005 to 1,000 stokes. The Direct Time
Method uses a single 3-line times tube for determining the "bubble seconds", which may then
be converted to stokes.
This method is considerably accurate, but the measurements can vary due to variances in
buoyancy because of the changing in shape of the bubble in the tube However, this does not
cause any sort of serious miscalculation.
Micro-Slit Viscometers
Viscosity measurement using flow through a slit dates back to 1838 when Jean Lonard
Marie Poiseuille conducted experiments to characterize the liquid flow through a pipe. He
found that a viscous flow through a circular pipe requires pressure to overcome the wall shear
stress. That was the birth of Hagen-Poiseuille flow equation. The slit viscometer geometry
has flows analogous to the cylindrical pipe but has the additional advantage that no entrance
or exit pressure drop corrections are needed. Detailed information regarding the
implementation of this principal with modern MEMS and microfluidic science is further
explained in a paper by RheoSense, Inc.
Generally, the slit viscosity technology offers the following advantages:
Measures true (absolute) viscosity for both Newtonian and non-Newtonian fluids[3] Enclosed system eliminates air interface and sample evaporation effects [4] Measurements can be made using very small sample volumes Laminar flow even at high shear rates due to low Reynolds number[5] Slit flow simulates real application flow conditions like drug injection or inkjetting.
Miscellaneous viscometer types
Other viscometer types use balls or other objects. Viscometers that can characterize non-
Newtonian fluids are usually called rheometers or plastometers.
In the I.C.I "Oscar" viscometer, a sealed can of fluid was oscillated torsionally, and by clever
measurement techniques it was possible to measure both viscosity and elasticity in the
sample.
The Marsh funnel viscometer measures viscosity from the time (efflux time) it takes a known
volume of liquid to flow from the base of a cone through a short tube. This is similar in
principle to the flow cups (efflux cups) like the Ford, Zahn and Shell cups which use different
shapes to the cone and various nozzle sizes. The measurements can be done according to ISO
2431, ASTM D1200 - 10 or DIN 53411.
The Flexible blade rheometer improves the accuracy of measurements for the lower viscosity
range liquids utilizing the subtle changes in the flow field due to the flexibility of the moving
or stationary blade (sometimes called wing or single side clamped cantilever).
Sumber : http://en.wikipedia.org/wiki/Viscometer ,( diunduh pada tanggal 12 oktober 2013 pada
pukul 12.15 wib).
Nama : Irwan jaya
Prodi : teknologi pengolahan pulp and paper
NIM : 012.12.001
