KERN & Sohn GmbH Ziegelei 1 D-72336 Balingen email: info@kern-sohn.com 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.
KERN PBS-A03/A04 GB Version 1.3 01/2012 Operating instructions Set for density determination for precision balances KERN PBJ/PBS Contents: 1 INTRODUCTION ............................................................................................................................ 3 1.1 1.2 SCOPE OF SUPPLY .................................................................................................................... 3 DIMENSIONS..........................................................................
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.
1. Weighing tray holder 2. Combination weighing tray 3. Container table 4. Container 5. Weighing tray carrier, 4 items 6.
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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.
5. Place the container table in a way that it does not touch the balance tray holder. B A 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.
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 ]. ρ= m 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.
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.
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.
4.2 Input „Density measuring liquid“ TARE / Press , 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. UNIT Use to increase the numeric value of the flashing cipher. PRINT Use to move the number selection to the right, the respective active position flashes.
4.3 Measurement „Density solid material“ UNIT 1. Repeatedly press 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. TARE / 2. Press (no change of the display). 3. Place sample in the upper sample dish. 4. Wait for stability display, then press CAL MENU . May be that „dSP pL“ can be displayed, but in that step this isn’t any error message and can be ignored. 5.
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 UNIT Switch-on balance, repeatedly press the key until the balance is in weighing mode.. Place sinker in the upper sample dish.
The volume of the sinker is computed by applying the following formula. V A B ρW = volume of sinker = weight of the sinker in air = 99.998 g = weight of the sinker in water = 87.607 g = 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.
UNIT Switch-on balance, repeatedly press the 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.
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.
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.
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.
7 Density Table for Fluids Temperatur Density p [g/cm3] e [°C] Water 10 0.9997 11 0.9996 12 0.9995 13 0.9994 14 0.9993 15 0.9991 16 0.9990 17 0.9988 18 0.9986 19 0.9984 20 0.9982 21 0.9980 22 0.9978 23 0.9976 24 0.9973 25 0.9971 26 0.9968 27 0.9965 28 0.9963 29 0.9960 30 0.9957 31 0.9954 32 0.9951 33 0.9947 34 0.9944 35 0.9941 PBS-A03/A04-BA-e-1213 Ethyl alcohol 0.7978 0.7969 0.7961 0.7953 0.7944 0.7935 0.7927 0.7918 0.7909 0.7901 0.7893 0.7884 0.7876 0.7867 0.7859 0.7851 0.7842 0.7833 0.7824 0.7816 0.
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) 1 10 50 100 500 1000 2000 3000 4000 0.0003 0.001 0.
9 User Instructions • To form a reproducible mean value several density measurement are necessary • Remove fat from solvent-resistant sample / sinker /beaker. • Regularly clean sample dishes/ sinker/beaker, do not touch immersed part with your hands • Dry sample/ sinker/pincers after each measurement. • Adjust sample size to sample dish (ideal sample size > 5 g). • Only use distilled water.
