Analytical Balances

An analysis is generally a detailed study and investigation. If this analysis includes the determination of weights, the balances used are called the analytical balances. The term “analytical balances” is also used for scales with a particularly high resolution.
Depending on the application, the analytical balances can offer additional functions. These include, for example, piece counting, percentage- and recipe weighing and density determination. If the analytical balances are used permanently, a short stabilization time (settling time) should be taken into account when making the choice.
If the values determined with the analytical balances are saved in the PC or processed further, it is advantageous if the analytical balances have an interface for data transmission. Via such interfaces, even the label printers can be connected to the analytical balances.
Special requirements must be met when it goes about the positioning of the analytical balances. The higher the resolution of the analytical balances is, the less the ambient conditions may fluctuate. This affects temperature and humidity as well as air movements. Also vibrations as well as static or magnetic charging of the analytical balances may cause an undesirable influence on the weighing results.
Analytical balances with a higher resolution usually have a draft shield in order to minimize the effects on the weighing sample caused by the ambient air. When the demands on weighing accuracy are extremely high or the frequent disturbances due to vibrations occur, the analytical balances are also placed on a special anti-vibration table. This well-damped weighing table can be precisely leveled and absorbs vibrations.

Instructions for using the analytical balances:

- observe the warm-up time for the analytical balances (usually approx. 30 minutes after switching on)
- observe the ambient temperature, see nameplate on the analytical balances
- adjust the temperature of the goods to be weighed to the temperature in the weighing room so that the weight did not increase because of the condensate from the room air
- align the analytical balances with the adjustable feet, the air bubble of the level control must be in the center of the marked circle
- do not operate other electrical devices close to the analytical balances in order to avoid magnetic interference
- use wind protection to exclude the impact occurring from the air movements
- pay attention to the residues on the weighing vessel, wear gloves if necessary
- place the goods in the middle
- calibrate the analytical balances regularly

A special form of the analytical balances is the moisture analyzer scales. The water content of the samples can be determined with these analytical balances. For this purpose, a heatable drying chamber is integrated in the compact scales. The sample is first weighed wet and then heated so that the water it contains evaporated. The weight is under constant monitoring. The analytical balances can stop the heating automatically when there is no more weight loss. Due to drying the small amounts of sample until the constant weight is achieved directly in the analytical balances, moisture analyses become faster and easier. The weight and dimensions of the sample are limited because of the compact design of the analytical balances.
According to the Measuring and Verification Ordinance, the scales for certain applications must be verified.
Among other things, this affects:

1 the analytical balances used for business or official purposes.
2 the analytical balances with which the mass is determined during
(a) the manufacture of the medicinal products in the pharmacies on the basis of a medical prescription or
(b) the analyses in the medical and pharmaceutical laboratories
3 the analytical balances for weighing patients for medical monitoring, examination and treatment.

The obligation to verify also applies to all analytical balances used for weighing such products as tea or spices for sale and any analytical balances used to determine fees, duties or penalties based on weight.

Before making a decision on the analytical balances, accuracy and resolution, depending on the application, must be determined. Here is an overview of accuracy classes and calibration values



Calibration values (e), less than 1 milligram, are not possible. The resolution (d) of the analytical balances can be equal to the calibration value, but can also be 10-fold or 100-fold for fine scales.
The official minimum load (min) for the analytical balances is the calibration technical lower limit of the weighing range and should not be confused with the minimum initial weight. The minimum or minimum weight implies to be the smallest mass that can be weighed with the analytical balances at a specified accuracy (e.g. 1% accuracy for medical drugs).
Calibrated analytical balances of accuracy class I or II can be used for pharmaceutical production. The Deutsche Apothekerzeitung [DAZ 39/2016] (German Pharmacist Newspaper) gives the following examples for the selection of the resolution in the analytical balances:

a) to weigh out 10.0 g of the medical substance. The required accuracy of 1% corresponds to 0.1 g
The drug can be weighed in with an analytical balance with a resolution of 0.1 g.
b) the drug mass to be weighed is 0.05 g, the 1% accuracy is 0.0005 g.
Here, the analytical balances that can display 0.5 mg steps must be used.

Due to the location-specific gravity, the weighing results of the analytical balances also depend on the geographic location of the installation site. The corresponding information may be found in a technical paper of the Physikalisch-Technische Bundesanstalt Braunschweig: "Above all, modern electronic scales ... are sensitive to changes in gravity depending on the geographical latitude φ and the height above sea level h. Both precision balances ... as well as commercial balances ... must therefore be adjusted at their place of use. ”With a defined gravitational zone, the analytical balances can also be finally adjusted by the manufacturer and used within the defined zone.

Analytical balances of accuracy class 1 always have an internal adjustment function that adjusts the analytical balances precisely to the respective site conditions, independent of the user. The analytical balances of accuracy class II can be adjusted either via an internal automatic adjustment or externally, i.e. by placing the tested external weights. If the analytical balances are not calibrated, the user can carry out the adjustment. The calibrated analytical balances may only be adjusted by the authorized persons (calibration officers or approved repairers).