Sartorius 2406 User guide

Digital Micro Balances
2406
Instructions for Installation and Operation

2
Unpacking 3
Installation 4
Checking 11
Weighing I 14
Weighing II 15
Checking of Balance Type 2406 16
Accuracy of Weight set 16
Correction of the Weighing Result 17

3
Unpacking
Remove Styropor insert from carton
1
Open Styropor box and lift balance out.
2

4
Installation
Make sure that the floor is level, that you have a sturdy
table, that there is no direct exposure to heat radiation or
sun light, draft or vibrations.
Recommended room temperature: 25°C,
relative humidity 60% ± 5%
Unpack accessories.
3
Weight knob indication: „19,99".
4
Positions of beam release lever:
1. Beam fully arrested
2. Beam in half release position — dial weights
3. Beam fully released
5

5
Remove outer and inner lid.
6
Remove glass plate from weighing compartment.
Check operating voltage:
7
Place the balance with its back-side on the dust cover,
open cover in the base plate, change connecting wires, if
necessary.
8

6
Remove brackets at the ends of the locking bars for the
weight knobs.
9
Pull out bars sideways, be sure that no ring weights
remain in the recess at the end of the bars.
10
Detach tapes from damping pot and remove cover
backwards.
11

7
Loosen nuts, swing aside springs and retighten nuts.
12
Loosen nuts, swing aside springs and retighten nuts.
13
Loosen nut, swing aside spring and retighten nut.
14

8
Remove beam, take off cardboard strip. Inspect knife
edges and arrestment pins for cleanliness.
Place beam on the arrestment pins.
15
Turn cover of damper until it stops.
16
Inspect stirrup plate for cleanliness and install („V" on the
top of the plate faces toward the front of the balance).
17

9
Remove stirrup arrestment bow.
18
Advance stirrups slightly, insert bow. „V" on the top of the
plate faces toward the front of the balance.
19
Place stirrups on stirrup plate.
20
Attach pan bow.

10
Attach pan, swing in pan lifting device. Turn mechanical
weight indicator and micrometer to zero. Level balance by
observing the spirit level.
21
Attach lamp housing. Connect balance to alternating
current line.
22

11
Checking
Arrest balance in half release position (beam release lever up).
Focus scale image on screen.
23
To adjust light intensity: Loosen knuried nut.
Center lamp bracket and retighten nut. Arrest beam.
24

12
For zero point and sensitivity control both lids must be in
place.
Release beam. Adjust zero point.
25
lf the zero point cannot be adjusted by means of this
knob, remove lids:
Direction of rotation if indication is – u
Direction of rotation if indication is – v
26
Control of sensitivity: Place a 10 mg weight on the pan.
Set indication of mechanical weights to „00.01". Release
beam and adjust zero point.
27

13
Set indication of mechanical weights to „00.00".
Scale must indicate exactly .„100".
28
Correction: Take out plug of lid.
Direction of rotation if indication is below „100"
Direction of rotation if indication is above „100"
29
Carry out alternating control of zero point and sensitivity
until both values are correct. Balance should be checked
and if necessary corrected after about one hour.

14
Weighing I
Adjust zero point. Swing pan out, introduce glass-tube and
swing pan back.
30
Arrest balance in half release position. Turn weight knob of
largest weight decade until scale swings back into the minus
area, then dial back one decade.
31
Proceed in the same way with the following smaller weight
decades. Arrest balance, and after a short time, release the
beam. When the optical scale has come to rest, turn micrometer
knob until the reading mark coincides with the center of a
division of the scale.
Weight indication: 12.104452 g
32
Check zero point after each weighing. In case of a
deviation, the weighing result should be determined from
the average value of both zero point readings.

15
Weighing II
Adjust zero point. Place objeet on the pan and return the pan to
the weighing compartment.
33
Move beam to the „half release" position. Turn knob of largest
weight decade until the scale Swings back to the minus area,
then turn weight knob back one decade.
34
Proceed in the same way with the following smaller weight
decades. Arrest balance and after a short time release the
beam. When the optical scale has come to rest, turn micrometer
knob until the reading mark is in the center of a division of the
scale.
Weight indication: 2.142672 g
35
Check zero point after each weighing. In case of a
deviation, the weighing result should be determined from
the average value of both zero point readings.

16
Checking of Balance Type 2406
1. Set mechanical weight indicator to „19.99".
2. Take the pan out.
3. Pull off lamp bracket.
4. Take off outer and inner lids.
5. Lift stirrup bow slightly and take stirrup plate off.
6. Pull off lid of damping pot (towards rear).
7. Carefully take out the beam.
8. Make sure that knife edges and bearings are
clean.
9. For cleaning use chamois or lenspaper. lf
necessary clean all bearing surfaces with alcohol
and wipe after drying.
10. Install balance in reversed order 7—1.
11. Check and adjust balance.
Accuracy of weight set
lt is practically impossible to adjust all weights to a degree
of perfection that errors can be eliminated completely.
Weights can also change due to contamination etc.
For this reason the initial and final weighings should be
carried out with the same weight combinations. Weight
discrepancies can be determined with the highest
possible accuracy by means of the wide range of the
10 mg scale.

17
Correction of the weighing result
The built-in weights above 0.1 g are of non-corrosive non-magnetic steel (density 7.88 g/cm3). The
weights below 0.1 g are made of a special aluminum alloy (density 2.7 g/cm3). For medium air
density of 0.0012 g/cm3they are adjusted to match brass weights of density 8.4 g/ml. Differential
weighings of the same material do not require a correction. In case of absolute weighings the
corrected result in consideration of the accuracy of the weight set (maximum error ± 21 µg) is
determined as follows:
Mp= N1+ N2+ K
vULvULvULvUL
K = N1(9.4 ∙10-6 - vUG1
+
vUP) + N2(3.0 ∙10-4 - vUG2
+
vUP)
MpMass of sample material
N1Indication of mechanical weights 19.9 ... 0.0 g
N2Indication of mechanical weights 0.09 ... 0.00 g
vULDensity of air
vUPDensity of sample material
vUG1 Density of built-in steel weights = 7.88 g/cm3
vUG2 Density of built-in aluminum weights = 2,7 g/cm3

18
The determination of atmospheric pressure and its influence on analytical weighings
The demands in respect to the accuracy of analytical and especially of micro-analytical weighings
are often extreme. Even though the accuracy required for the end result is usually only 1 %, the
requirement of a much higher accuracy is conditioned by the necessity of also having to weigh the
mass of the tare which often exceeds to a considerable degree that of the proper sample.
In Order to improve accuracy, it is necessary to systematically eliminate all sources of errors. One
of the most critical factors in this respect is the elimination of the influence of the air buoyancy. To
what extent it may be necessary to take this factor into account, depends — aside from the
required tolerances - on the specific weight of the sample in relation to that of the weights used.
Felgentraeger1) in “Feine Waagen, Waegungen und Gewichte" draws attention to the fact that
most chemists either are not aware of the significance of air buoyancy or fall to do anything about it
because the procedure seems too complicated.
The tables provided by that author furnish the necessary information for all respective calculations
up to the most exacting requirements. Lately, H. Ulbricht has published two papers on the
significance of air buoyancy2). These publications give information only on the importance of air
buoyancy without furnishing data on how to determine it. It is exactly this point, however, which
causes difficulties.
The tables found in Kohlrausch and D'Ans/Lax3) can be used only for a coarse reduction of mass
relative to vacuum at normal air pressures. They cannot be used for determining changes in
buoyancy caused by variations of atmospheric pressure.
This paper presents an attempt at furnishing to the chemist information which will enable him in a
simple manner to determine atmospheric pressure and to use this information for analytical
weighings. lt is hoped that in this way a contribution is being made towards the full utilization of the
inherent accuracy of modern analytical balances by those who need it.
One must first distinguish between the determination of the absolute mass i.e. the reduction of the
found values to vacuum atmosphere and the determination of the influence of changes of air
buoyancy. The latter are significant also in „relative" weighings.
Usually, only the second case will be of practical interest. Since the required corrections in this
case amount to only 1/10th of those required in the first instance, it may, sometimes, be
unnecessary to apply these corrections at all. This does not mean that one should not be aware of
the magnitude of correction and consider the questions of its application.

19
Calculating variations of atmospheric pressure
The atmospheric pressure is governed by the barometer reading, which in turn depends on
temperature and absolute air humidity. The latter can be determined from the relative humidity and
temperature. The following equation indicates the relation between the change of air pressure UD
in % and these factors. Herein, Ub is the Variation of the barometer reading in mm of mercury, Ut
the change in temperature, t the temperature in °C and Uf the change of the relative humidity in %.
(1) UD = 0,13 Ub - 0,35 Ut – 0,0005 t ∙Uf [%]
Thus, a change of air buoyancy of 0.1 % is caused at t = 20° by a change in air pressure of
Ub = + 0.8 mm Hg or a temperature Variation of Ut = - 0.29° or a change in humidity of
Uf = -10%.
This equation applies in the range from 5 to 30°C. The tables, fig. 1 facilitates the use of this
equation since the three factors can easily be found there.
One can see at first glance that the effect of humidity changes is relatively small for which reason it
can often be disregarded. The following example is indicative of the actually possible conditions:
The temperature in a laboratory may be 17°C in the morning and 21° in the afternoon when a
weighing is repeated which was first made in the morning. lf one assumes that during the same
time, the humidity fell from 50% to 40% and the barometer from 758 to 755, which variations are
not uncommon, then using fig. 1, we obtain:
UD = -0,4 – 1,4 - +0,1 = -1,7%
Fig. 1 Diagram to ascertain variation of air buoyancy. To determine the influence of humidity read from percentage of Variation of
humidity to the left to temperature (not difference of temperature). Read Variation of air buoyancy below. Then add results of
Variation of temperature,
The buoyancy of the air decreased by approx. 2%. The following example shows the effect of this
change on the evaluation of a weighing.

20
Calculating the buoyancy difference
Since the buoyancy is the weight of the replaced
vUL
(2) A = vUS∙M
the change of the buoyancy is
UA UA
(3) M = 12 ∙vUS10-6
wherein UD must be entered as % age. If M is given in grams, UA result from equation (2) by
entering for air buoyancy vULthe median value of 1,2 x 10 –3 g/ml.
Example:
For M = 100 g and vUS= 1 the relative change of mass for the air buoyancy change of - 1,7 % is:
von 1
107112 6
−
−∙,∙= 20 ∙10-6, i.e. for 1 g of
the sample weight the difference is 20 µg, for 100 g. 2.0 mg.