Frequently asked question
Which scale to choose for weighing powdered medications?
It is essential to ask yourself the following questions before purchasing a scale intended for weighing medications to treat aquarium fish:
- What precision are we trying to obtain?
- What maximum weight should it weigh? (maximum load or reach)
- What minimum weight should it weigh? (minimum range)
- In what environment will it be used? (dust and humidity)
Precision classes
The first criterion to take into account is the precision of the balance. There are four classes of precision recognized at European level:
- I (Special): analytical balances (research and development in the food industry, hospitals, etc.)
- II (Fine): precision balances (pharmacies, medical analysis laboratories, etc.)
- III (Medium): industrial scales (industrial production, logistics, etc.), medical (medical scales), commercial (bakery, butchery, fishmonger, greengrocers, market sales, etc.)
- IV (Ordinary): ordinary scales (kitchen, pocket etc.)
The accuracy class is determined by the ratio between the maximum load of the scale (the range) and the scale (directive 2009/23/EC, annex I, paragraph 2.1).
Class Verification scale (e) Minimum rangeNumber of verification steps (n = range / e) n minimum n maximumI Special e ≥ 0.001 g 100 e 50,000 - II Fine 0.001 g ≤ e ≤ 0.05 g e ≥ 0.1 g 20 e 50 e 100 5,000 100,000 100,000 III Average 0.1 g ≤ e ≤ 2 g e ≥ 5 g 20 e 20 e 100 500 10,000 10,000 IV Ordinary e ≥ 5 g 10 e 100 1,000
The maximum range corresponds to the maximum load that the scale can measure.
The scale (e) is the difference between 2 consecutive indications for a digital indicator. This is the smallest value that the instrument is capable of displaying as the mass increases.
The smaller the scale, the more precise the balance. In general, the verification scale corresponds to the display accuracy. This is the case for class II to IV balances.
The range and the scale are closely linked. A scale that accepts a large load will in fact be less accurate than a scale that accepts a very small load.
The graduation (d) (also called reading) is the smallest readable value of the weight in each range on the display.
The meaning of the minimum range is not clear: it may refer to the minimum weight that the scale is capable of displaying or to the minimum weight recommended for precise measurements. For approved scales, they will not operate below this value (the tolerated error is then so significant in relation to the load that use for a regulated application is not permitted). 200 g / 0.1 g = 22,000 scales therefore a class II balance Attention: it will not be able to weigh weights less than 0.5 g (manufacturer data) or even 5 g (50 e) for regulated applications!
Protection index against dust and humidity
The IP protection index is an international standard relating to the waterproofness of weighing instruments. The first number indicates the level of protection against solid bodies and the second against liquid bodies. The higher the number, the better the protection of the balance.
The coding of the IP indices:
Index
1st digit (solid bodies)
2nd digit (liquid bodies)
0
No protection
No protection
1
Protection against higher solid bodies at 50 mm
Protection against vertical falling drops of water
2
Protection against solid bodies greater than 12 mm
Protection against falling water with a maximum inclination of 15°
3
Protection against solid bodies greater than 2.5 mm
Protection against water in rain (max. inclination. 60°)
4
Protection against solid bodies greater than 1 mm
Protection against splashing water
5
Protection against dust
Protection against jets of water
6
Total protection against dust
Protection against strong jets of water
7
Protection against the effects of temporary immersion
8
Protection against the effects of submersion (max. 30 min.)
9
Protection against the effects of submersion and high-pressure cleaning pressure
9K
Protection against high pressure and high temperature cleaning