KERN PBS-A03 User manual

KERN & Sohn GmbH
Ziegelei 1
D-72336 Balingen
email: [e-mail]
Phone: +49-[0]7433- 9933-0
Fax: +49-[0]7433-9933-149
Internet: www.kern-sohn.com
Operating instructions
Density Determination Set
KERN PBS-A03/A04
Version 1.3
01/2012
GB
PBS-A03/A04-BA-e-1213

2 PBS-A03/A04-BA-e-1213
GB
KERN PBS-A03/A04
Version 1.301/2012
Operating instructions
Set for density determination for precision balances
KERN PBJ/PBS
Contents:
1INTRODUCTION ............................................................................................................................ 3
1.1 SCOPE OF SUPPLY.................................................................................................................... 3
1.2 DIMENSIONS............................................................................................................................. 5
2INSTALLING THE DENSITY DETERMINATION SET.................................................................. 6
3PRINCIPLE OF DENSITY DETERMINATION............................................................................... 8
3.1 INFLUENCING MAGNITUDES AND ERROR SOURCES...................................................................... 9
4DENSITY DETERMINATION OF SOLIDS................................................................................... 10
4.1 ACTIVATE FUNCTION............................................................................................................... 10
4.2 INPUT „DENSITY MEASURING LIQUID“ ....................................................................................... 11
4.3 MEASUREMENT „DENSITY SOLID MATERIAL“............................................................................. 12
5DETERMINING DENSITY OF LIQUIDS ...................................................................................... 13
5.1 VOLUME DETERMINATION OF THE SINKER................................................................................. 13
5.2 DENSITY DETERMINATION AT KNOWN VOLUME OF THE SINKER................................................... 14
6PRECONDITIONS FOR PRECISE MEASUREMENTS............................................................... 16
6.1 CALCULATION OF RESULTS..................................................................................................... 16
6.2 INFLUENCE FACTORS FOR MEASUREMENT ERRORS ................................................................. 17
6.2.1 Air bubbles....................................................................................................................... 17
6.2.2 Solid body sample ........................................................................................................... 17
6.2.3 Liquids.............................................................................................................................. 17
6.2.4 Surface............................................................................................................................. 17
6.2.5 Sinker for liquid density measurement ............................................................................ 17
6.3 GENERAL INFORMATION.......................................................................................................... 18
6.3.1 Density / Relative Density................................................................................................ 18
6.3.2 Drift of Balance Display ................................................................................................... 18
7DENSITY TABLE FOR FLUIDS................................................................................................... 19
8UNCERTAINTY OF MEASUREMENT FOR DENSITY DETERMINATION OF SOLIDS............ 20
9USER INSTRUCTIONS................................................................................................................ 21

PBS-A03/A04-BA-e-1213 3
1 Introduction
KERN PBS-A03 KERN PBS-A04
•Set for density determination for
precision balances of the series
KERN PBJ/PBS with big weighing
plate (180 x 170 mm).
•Set for density determination for
precision balances of the series
KERN PBJ/PBS with small
weighing plate (105 x 105 mm).
•When using the density set, the
capacity of the balance is reduces
by approx. 100 g.
•When using the density set, the
capacity of the balance is reduces
by approx. 290 g.
•In order to guarantee a safe and trouble-free operation, please
read carefully the operating instructions.
•These operating instructions only describe the operation of the
density determination set. For further information on how to
operate your balance please refer to the operating instructions
supplied with each balance.
1.1 Scope of supply
Fig. 1: Installed density set KERN PBS-A04

4 PBS-A03/A04-BA-e-1213
1. Weighing tray holder
2. Combination weighing tray
3. Container table
4. Container
5. Weighing tray carrier,
4 items
6. Glass sinker

PBS-A03/A04-BA-e-1213 5
1.2 Dimensions

6 PBS-A03/A04-BA-e-1213
2 Installing the density determination set
•If necessary, carry out necessary adjustment before installation of the density
set.
•When the density set is installed, correct adjustment is not possible.
•For reasons of adjustment, take away the density set and place the standard
weighing plate.
•The following pictures show the density set KERN PBS-A03 at a balance with
big weighing plate. The density set KERN PBS-A04 must be installed at the
same way.
1. Switch off balance and separate it from the power supply.
2. Remove standard weighing plate.
3. Remove carrier of the standard
weighing plate and replace by
weighing tray carrier of the density
set.
4. Put balance tray holder according to
fig. into the four balance tray carriers.
Thereby observe the right position,
the openings on the upper side must
point forwards.

PBS-A03/A04-BA-e-1213 7
A
B
5. Place the container table in a way
that it does not touch the balance tray
holder.
6. Put the containers in the center of the
container table
7. Hook up the combination balance
tray according to illustration; ensure
that it does not touch the container.

8 PBS-A03/A04-BA-e-1213
ρ = A
A-B o
ρ
ρ =
m
V
3 Principle of Density Determination
Three physical magnitudes are the volume and the mass of bodies as well as the
density of matter. In density mass and volume are related.
Density [ ρ] is the relation of mass [ m ] to volume [ V ].
SI-unit of density is kilogram divided by cubic meter (kg/m³). 1 kg/m³ equals the density of
a homogenous body that, for a mass of 1 kg, has the volume of 1 m³.
Additional frequently applied units include:
1g
cm
3
,
1kg
m3
,
1g
l
The application of this density determination set in combination with the KERN PBS/PBJ
balances provides fast and safe determination of solids and fluids. Our set uses the
"Principle of Archimedes" to determine density:
BUOYANCY IS A FORCE. IT AFFECTS A BODY THAT IS IMMERSED INTO A FLUID. THE BUOYANCY
OF THE BODY EQUALS THE WEIGHT FORCE OF THE DISPLACED FLUID. THE FORCE OF
BUOYANCY ACTS VERTICALLY UPWARDS.
Thus, density is calculated according to the formulae below:
Determining density of solid bodies
Our balances enable weighing of solids in air [ A ] as well as water [ B ]. If the density of
the buoyancy medium is known [ ρo ] the density of the solid [ ρ] is calculated as follows:
ρ= density of sample
A = weight of the sample in air
B = weight of sample in measuring fluid
ρo = density of measuring fluid

PBS-A03/A04-BA-e-1213 9
ρ =
V
A-B L
ρ
+
Determining density of liquids
The density of a fluid is determined with the help of a sinker providing a known volume [ V
]. The sinker is weighed in air [ A ] as well as in the test fluid [ B ].
According to the Archimedes’ Principle a body immersed in a fluid experiences a force of
buoyancy. [ G ]. This force equals the weight force of the fluid displaced by the volume of
the body.
The volume [ V ] of the immersed body equals the volume of the displaced fluid.
G = buoyancy of sinker
Buoyancy of sinker =
Weight of the sinker in air [ A ] -weight sinker in test liquid [ B ]
From this follows:
ρ= Density of test liquid
A = weight of sinker in air
B = weight of sinker in sample fluid
V = volume of sinker*
ρL = Air density (0.0012 g/cm³)
* If the volume of the sinker is unknown, this can be determined e.g. in water and be
calculated as follows, see chap. 5.1.
V = volume of sinker
A = weight of sinker in air
B = weight of sinker in water
ρW = density of water
3.1 Influencing magnitudes and error sources
Air pressure
temperature
Volume deviance of the sinker (±0,005 cm3)
Surface tension of the liquid
Air bubbles
Immersion depth of the sample dish of sinker
Porosity of the solid

10 PBS-A03/A04-BA-e-1213
4 Density determination of solids
For the density determination of solid material, the solid is weighed first in air and
then in the measuring liquid. From the weight difference results the buoyancy from
where the software calculates the density.
Prepare balance as described in chapter 2 "Installation of density determination
set".
Fill measuring liquid into the container. Filling height should be approx. ¾ of the
capacity. Heat measuring liquid until temperature is constant.
4.1 Activate function
Switch on balance
In weighing mode press repeatedly
MENU
CAL
until
„U“ flashes.
Press
TARE/
Press repeatedly
MENU
CAL
until „U-

d“ is
displayed.
From now on the balance is in density
determining mode for solids.

PBS-A03/A04-BA-e-1213 11
4.2 Input „Density measuring liquid“
Press
TARE/
, the density saved as last of the
measuring liquid is displayed. When changing by
the arrow keys, enter first the numeric value of
the density considering the current temperature
(see chap. 7), then set the decimal place.
Use
UNIT
to increase the numeric value of the
flashing cipher.
Use
PRINT
to move the number selection to the
right, the respective active position flashes.
Set decimal place
Take the last place using
PRINT
, when this place
dot is flashing, press
PRINT
anew . The decimal
place represented as „

“ appears.
Use
UNIT
to define the position of the decimal
place.
Acknowledge with
TARE/
.
Observe that the stability mark is displayed, if
not, the entry has not been accepted.
Press
ESC
ON/OFF
repeatedly or keep pressed for 3
sec until the gram display will appear.

12 PBS-A03/A04-BA-e-1213
4.3 Measurement „Density solid material“
1. Repeatedly press
UNIT
until the balance
is in density determination mode for solids.
May be that „dSP pL“ can be displayed, but
in that step this isn’t any error message
and can be ignored.

2. Press
TARE/
(no change of the display).
3. Place sample in the upper sample dish.
4. Wait for stability display, then press
MENU
CAL
.
May be that „dSP pL“ can be displayed, but
in that step this isn’t any error message
and can be ignored.
5. Place sample in the lower sample dish.
6. The density of the sample is shown.
To start the next measurement press
MENU
CAL
, before the current sample is removed
from the lower sample dish. For the new measurement start at step 2.
When using an other measuring liquid, start at the entry „Density measuring liquid“,
see chapter 4.2.
Using
UNIT
the balance returns into the weighing mode.

PBS-A03/A04-BA-e-1213 13
5 Determining density of liquids
5.1 Volume determination of the sinker
Prepare balance as described in chapter 2 "Installation of density determination set".
Fill water into the container. Filling height should be approx. ¾ of the capacity. Heat
sample liquid until temperature is constant.
Keep the sinker ready
Switch-on balance, repeatedly press the
UNIT
key until the balance is in weighing mode..
Place sinker in the upper sample dish. Wait for
stability display to appear; write down the
displayed weighing value.
Place sinker in the lower sample dish. Wait for
stability display to appear; write down the
displayed weighing value.

14 PBS-A03/A04-BA-e-1213
The volume of the sinker is computed by applying the following formula.
V = volume of sinker
A = weight of the sinker in air = 99.998 g
B = weight of the sinker in water = 87.607 g
ρW = density of water (see chap. 7) at 20°C = 0.9982 g/cm³
5.2 Density determination at known volume of the sinker
Prepare balance as described in chapter 2 "Installation of density determination set".
Fill test liquid in the container. Filling height should be approx. ¾ of the capacity. Heat
sample liquid until temperature is constant.
Keep the sinker ready

PBS-A03/A04-BA-e-1213 15
ρ = V
A-B
Switch-on balance, repeatedly press the
UNIT
key until the balance is in weighing mode..
Place sinker in the upper sample dish. Wait for
stability display to appear; write down the
displayed weighing value.
Place sinker in the lower sample dish. Wait for
stability display to appear; write down the
displayed weighing value.
The density of the test liquid is computed by applying the following formula.
G = buoyancy of sinker
Buoyancy of sinker =
Weight of the sinker in air [ A ] -weight sinker in test liquid [ B ]
From this follows:
ρ= density of sample fluid
A = weight of sinker in air
B = weight of the sinkers in test liquid
V = volume of sinker

16 PBS-A03/A04-BA-e-1213
ρ = A
A-B
o
ρ
6 Preconditions for Precise Measurements
There are numerous error possibilities during density determination.
Accurate knowledge and caution are required to achieve precise results when
applying this density set in combination with the balance.
6.1 Calculation of Results
The balance displays results for density determination by giving four decimal places.
However, this does not mean that the results are accurate down to the last decimal
place as this would be the case for a calculated value. Therefore all weighing results
used for calculations have to be examined closely.
Example for density determination of solids:
To ensure high-grade results, numerators as well as common denominators of the
formula below must show the desired accuracy. If either of them is instable or flawed,
the result, too, will be instable or flawed.
ρ= density of sample
A = weight of the sample in air
B = weight of sample in measuring fluid
ρo = density of measuring fluid
The use of a heavy sample contributes to the accuracy of a result. this increases the
numerical value. The use of a light-weight sample, too, contributes to the accuracy of
a result because this increases buoyancy (A-B). As a consequence, the result of the
common denominator increases. Bear also in mind that the accuracy of the density of
the measuring fluid ρoenters into the common denominator and, thus, has
considerable influence on the accuracy of the result.
The result for the density of the sample cannot be more accurate than the least
accurate of the aforementioned individual entities.

PBS-A03/A04-BA-e-1213 17
6.2 Influence Factors for Measurement Errors
6.2.1 Air bubbles
A small bubble of, for example, 1mm3 will have a considerable influence on the
measurement if the sample is small. Buoyancy will be increased by approximately 1mg
resulting immediately in an error of 2 digits. Hence, it has to be ensured that no air
bubbles cling to the solid immersed in the fluid. The same applies to the sinker that is
immersed in the test fluid.
Take great care when removing air bubbles by swirling, to prevent the fluid from spurting
out and splashing onto the sifting bowl or from water splashing. Moisture on the
suspension bracket of the sifting bowl results in increased weight.
Do not touch the solid sample or sinker with bare fingers. An oily surface causes air
bubbles when immersing the specimen in fluids.
Do not place solid samples (in particular flat objects) in the sifting bowls outside the liquid
as this would result in air bubbles when immersed together. For this reason examine the
bottom of the sifting bowl for air bubbles after the specimen had been immersed in fluid.
6.2.2 Solid body sample
A sample possessing too great a volume that is immersed in fluid will result in an increase
in fluid level inside the glass pitcher. As a result, part of the suspension bracket of the
sifting bowl will also be immersed causing buoyancy to increase. As a consequence the
weight of the specimen in the fluid will drop.
Samples that change the volume or assimilate fluid are unsuitable for measurement.
6.2.3 Liquids
Water temperature is another factor to be taken into consideration. The density of water
changes by c. 0.01% per degree Celsius. A temperature measurement showing an error
of 1 degree Celsius results in an inaccurate fourth decimal place.
6.2.4 Surface
The suspension bracket of the sifting bowl penetrates the surface of the fluid. This state
undergoes continuous change. If the sample or the sinker is relatively small, the surface
tension will impair repeatability. The addition of a small amount of detergent makes the
surface tension negligible and increases repeatability.
6.2.5 Sinker for liquid density measurement
To save precious specimen liquid, a small beaker and a sinker that fits such a beaker
are usually used to measure liquid density. However, note that a larger sinker will
bring higher accuracy.
Both the buoyancy and the sinker volume are desired to have as many significant
figures as possible for precise results. Because they are the numerator and
denominator of the expression to compute the liquid. Seeking accurate volume of the
sinker is also important.

18 PBS-A03/A04-BA-e-1213
6.3 General information
6.3.1 Density / Relative Density
Relative density follows from the weight of a specimen divided by the weight of water (at
4° Celsius) of the same volume. For this reason relative density does not have a unit.
Density equals mass divided by volume.
The application of the relative density instead of the density of a fluid in a formula
produces an incorrect result. In the case of fluids only their density is
physically meaningful.
6.3.2 Drift of Balance Display
The drifting of a balance does not influence the final result of the density determination
although the shown weight of weighing in air is affected. Accurate values are merely
required if the density of fluids is determined by means of a sinker.
When changing the ambient temperature or location, an adjustment of the balance is
necessary. For this purpose remove the density set and carry out adjustment using the
standard weighing tray (see operating instructions supplied with the balance).
.

PBS-A03/A04-BA-e-1213 19
7 Density Table for Fluids
Temperatur
e [°C]
Density p [g/cm3]
Water
Ethyl alcohol
Methyl alcohol
10
0.9997
0.7978
0.8009
11
0.9996
0.7969
0.8000
12
0.9995
0.7961
0.7991
13
0.9994
0.7953
0.7982
14
0.9993
0.7944
0.7972
15
0.9991
0.7935
0.7963
16
0.9990
0.7927
0.7954
17
0.9988
0.7918
0.7945
18
0.9986
0.7909
0.7935
19
0.9984
0.7901
0.7926
20
0.9982
0.7893
0.7917
21
0.9980
0.7884
0.7907
22
0.9978
0.7876
0.7898
23
0.9976
0.7867
0.7880
24
0.9973
0.7859
0.7870
25
0.9971
0.7851
0.7870
26
0.9968
0.7842
0.7861
27
0.9965
0.7833
0.7852
28
0.9963
0.7824
0.7842
29
0.9960
0.7816
0.7833
30
0.9957
0.7808
0.7824
31
0.9954
0.7800
0.7814
32
0.9951
0.7791
0.7805
33
0.9947
0.7783
0.7896
34
0.9944
0.7774
0.7886
35
0.9941
0.7766
0.7877

20 PBS-A03/A04-BA-e-1213
8 Uncertainty of Measurement for Density
Determination of Solids
This table shows the approximate readability of the balance in connection with the
density set. Observe that these values have only been determined by calculation and
that influent parameters such as described in chapter 6 have not been taken into
consideration.
Approximate display at density measurements
(when using a balance with a readability of 0.01g*)
Weight of sample
(g)
Density of sample
[g/cm
3
]
1 10 50 100 500 1000 2000 3000 4000
1
0.1
0.01
0.003
0.002
0.0005
0.0003
0.0003
0.0002
0.0002
3
0.4
0.04
0.01
0.005
0.001
0.001
0.0005
0.0004
0.0004
5
0.7
0.07
0.01
0.008
0.002
0.001
0.001
0.001
0.0006
8
1.2
0.1
0.02
0.01
0.003
0.002
0.001
0.001
0.001
10
1.5
0.1
0.03
0.02
0.004
0.002
0.001
0.001
0.001
12
1.7
0.2
0.04
0.02
0.004
0.002
0.002
0.001
0.001
20
2.9
0.3
0.06
0.03
0.01
0.004
0.003
0.002
0.002
*when using a balance with a readability of 0.1 g, the numbers in this table have to be
multiplied with 10. When using a balance with a readability of 0.001 g, divide the numbers
through 10.
Reading example for table:
In a balance with a resolution of 0.001 g and a sample with a weight of 10 g, whose
density is 5 g/cm3, the display graduation is at 0.007 g/cm3.