Laboratory scales - equipment designed to measure the mass of various objects and substances. Such devices can work, for example, from the network or from the battery. At the same time, modern equipment of this type is accurate. But the use of such scales, unlike conventional mechanical ones, is nevertheless laid exclusively in conjunction with special calibration weights.
What accuracy of indications can depend on
Scales of any kind are necessarily calibrated at the production site - at the last stage of manufacture. However, actually in laboratories or, for example, at home, such equipment may still be inaccurate. And this is often connected not at all with the fact that the defective product was sold to the consumer. The point in this case consists primarily in the fact that the accuracy of the readings of the scales can vary significantly depending on the area where they are used. The factors that influence this characteristic of devices include the following:
latitude of the area;
elevation above sea level;
power surges in the electric network;
changes in air temperature.
In order for the scales to give the most accurate readings, they need to be calibrated separately. Most often, a similar procedure is needed when buying a new device. Laboratory scales often need adjustment as well when changing a workplace. In some cases, this procedure is required even every time you turn it on. After all, laboratory measurements, of course, should be as accurate as possible.
Actually, to set up the scales, special elements are used - calibration weights . As already mentioned, they usually come complete with the measuring device itself. However, in some cases, these elements have to be purchased separately.
What are
Calibration weights are made in strict accordance with the requirements of GOST 7328 - 2001. Standards for their production must be followed. Externally, calibration weights are no different from ordinary ones.
According to the requirements of GOST, weights of this type are necessarily packed in individual cases. They are called either gauge or alignment proper.
What weights are used
Such weights are usually used with devices devoid of special internal calibration devices. This is the widest scope of their use. However, the internal calibration to ensure maximum accuracy of adjustment of the scales allows, unfortunately, not always. Therefore , if even such modern functional devices are available in the laboratory, it is still recommended to use calibration weights complete with them.
Main types
Calibration weights may vary:
If we talk about the form, then, as already mentioned, weights can be supplied to the modern market with or without a head. Heavy calibration elements of the first type in some cases have a channel in the upper part. This is how weights of 5 to 10 kg are made.
Denominations
According to clause 4.1 of GOST 7328-2001, the exact weight of the calibration elements should be 1x10n, 2x10n or 5x10n. The value of n in these formulas should be an integer from - 6 to +3, inclusive. Thus, the values of the calibration weights can be as follows: 1, 2 , 5, 10, 20, 50, 100, 500, 1000, 2000, 5000 , etc. milligrams, grams or kilograms.
GOST requirements in relation to the nominal weight of such elements, however, are not always observed in their production. Some enterprises make calibration weights for scales, guided by the recommendations of TU. Such elements can have any face value.
In any case, with each weight packed in a case, a certificate must be supplied confirming its compliance with the requirements of GOST or TU. In this document, among other things, the exact weight of the element is indicated.
Actually, the very requirements for the required weight of the calibration weights are indicated in the passport of the laboratory balance.
Production material
Weights of this variety are made, of course, exclusively from metal. This material is durable and easy to clean. Indeed, by definition, there should be no dirt or dust on such elements in any case. The following types of metals can be used for the manufacture of weights:
aluminum;
stainless steel;
nickel silver;
non-magnetic steel.
Stainless steel is usually used for the manufacture of weights without heads, non-magnetic - with heads. Aluminum is most often used in the production of very small calibration elements, the mass of which ranges from 1 to 5 mg. Neisilber is used for the manufacture of weights of 10 - 500 mg. If the weight of the calibration weight is 1 kg, 5, 10 kg, etc. , most likely it will be made of steel. It is this material in this case that requires the use of GOST.
Accuracy classes
On this basis, calibration weights are divided according to the values of metrological characteristics. There are only seven accuracy classes for such elements:
E 1 . Weights of this class are used to check laboratory weights of the first class.
E 2 . E2 calibration weights are used in conjunction with weights of accuracy classes F1, the first and second special.
F1. Weights of this type are usually used to check the weight of other weights - F2, as well as laboratory scales of the second accuracy class.
F2 . Such weights are used to check the scales of the second high and third middle accuracy classes.
M 1 . These elements are used in conjunction with scales of technical accuracy class or when weighing medicines.
M 2 and M 3 - weights used in trade scales when balancing the mass of the cargo.
Calibration weights 200 g , 1 kg, 5 mg and other nominal weights assigned to classes E and F in our country today are made mainly according to German technology and in compliance with not only GOST, but also international standards R111 OIML.
Ways to use
On this basis, ordinary calibration weights and reference weights are distinguished. The latter variety of elements is used to test model electronic or mechanical scales. Reference weights, in contrast to conventional calibration weights, are supplied to the market not with certificates, but with a special inspection certificate.
Calibration Kits
Similar elements can be delivered to the market, including in sets. Such products on the modern market are also quite in demand. Sets differ primarily in accuracy class. Also, weights of different nominal weights may be included in the kits. That is why using them is usually very convenient.
The set may include calibration weights of 20 kg, 200 g, 1 mg, etc. But in any case they fit, like individual elements, into special cases. This helps to prevent damage to weights, and consequently, their complete loss of operational properties.
Consumer Reviews
According to most experts who use high-precision scales in their work, weights made using modern technologies almost always have excellent quality. After all, it is not for nothing that such elements are delivered to the market with certificates.
On the sets of weights from experts, there are basically only good reviews. Using such kits, as already mentioned, is almost always very convenient. Moreover , the sets of calibration weights can also include instruments designed to work with them. This can be, for example, tweezers, cotton gloves, brushes, etc.
How to calibrate the balance
The actual procedure for setting up a laboratory measuring device using weights is called external. There is also an internal calibration. However, this operation is carried out using not weights, but special internal reference weights.
Calibration technology is selected primarily taking into account the design of the balance and the instructions for use attached to them. But in any case, most often this procedure looks like this:
scales are included in the network;
the display is reset;
by pressing a special key, the balance is transferred to calibration mode;
after the zero point is highlighted, it is confirmed by pressing the key;
after highlighting the maximum load indicator, a calibration weight is placed on the weighing platform ;
zero point is confirmed.
After the inscription confirming the accuracy of calibration is displayed on the screen, the weight is removed from the platform. Immediately after this, the laboratory balance automatically switches to standard operating mode.
If necessary, after calibration, the balance can be additionally checked for accuracy. To do this, you need to put the adjustment weight on the platform again. If the scale shows its nominal weight, marked in the certificate - then everything is in order. Scales can be used in work.