Laboratory Balances

Scales and balances have become a must-have instrument which finds its application almost in all spheres of life: at the enterprise, at the store or market, at home, variety of manufacturing companies – anywhere where the goods / materials / substances should be weighed. Since there are numerous fields of application, there are lots of types of balances which may be better and more suitable for this or another purpose. Mostly all laboratory scales used today are electronical, possessing sensors and lighted display for convenience.

When it goes about laboratory, it is clear that approximation does not count and all the measurements should be as precise and accurate as possible. The first thing to remember is that it goes about accuracy and this should not be underestimated. Connected with this point is also specialization of the laboratory, because depending on what kind of tests and experiments are carried out there, the laboratory balances applied may also differ. In general, the laboratory balances may be analytical (with the highest precision class 1, 2), technical, microbalances, top loading balances and others. There is simply no point to take the highest precision analytical balances for weighing materials where the highest accuracy is not necessary. Thus, for example, in metallurgical, heavy industries, agriculture, partly chemical and food industries, the laboratory balances weighing is often carried out not in the perfect ideal conditions (dust, vibration, wind) and the analytical balances may just be not the best choice. More robust models providing smaller accuracy, but provided with additional auxiliary equipment (weighing platform, windscreen, removable weighing pans) may serve for weighing samples of hot substances, oil, coal products without being damaged or broken. They are easy to maintain, clean and calibrate due to the automatic calibration function.

In their turn, analytical balances are mostly used for especially precise measurements, where not only gram, but hundreds of a gram count. This applies mostly to pharmaceutical and medical sphere (preparation of solutions, testing of new substances, mixing of various component), jewelry production, chemical laboratories, food / beverages production (creation of new tastes and flavors), criminalistics etc. The requirements to this type of balances are very high and that is why these analytical devices should fully comply with the regulations of ISO and GLP. Depending on the accuracy a certain laboratory is certified for, the equipment used in this laboratory is strictly controlled. Compliance with all the requirements is important not only for the laboratory where the experiments are carried out, but at all the further stages the product goes through: developing, processing, manufacturing, packaging, storage… The main goal is – the final product which in this or another way reaches the customer should correspond to the existing required standards. That is why GMP (Good Manufacturing Practice) or BRC Global Standards, which, principally, monitor and control that the producer observed all the rules at any stage the product goes through, in order the customer / consumer received qualitative product, set very high requirements which are obligatory for fulfillment.

To use these balances, the perfect conditions must be provided: absolutely clean air, no contaminants, like dust or particles of other substances, cleanness, absence of vibration, air flow, draft. If some of the parameters cannot be fulfilled, like very clean environment, the balances need to have a special protection class, which correspondingly prevents contaminants from getting inside and influencing the measurements. It mostly goes about weighing samples of bulk or liquid test reagent, chemical agents with the purpose to determine very precise weight, up to 5th decimal place. This type of balances may be used only be the trained personnel and the equipment should be installed on a special anti-vibration laboratory table, so that any possible influence on the measuring process was excluded.

Nowadays, the latest models of the laboratory scales possess a special interface – this feature provides the connection to the computer and a very good possibility to process and analyze the results of the measurement at once. All the data are stored and the influence of the human factor is almost brought to zero. Due to the software, the data cannot be confused, misread or lost, and almost all necessary calculations are carried out automatically. Laboratory balances must be calibrated regularly, especially the analytical ones, in compliance with the directives concerning quality control. The slightest changes in the environment (temperature, humidity, air moves, pressure) are likely to affect the weighing equipment and thus, to ensure perfect measurement results. Calibration may be external and internal, can be carried out manually by the trained operator or automatically, if there is such a function available. Laboratories that comply with ISO/GLP or GMP are recommended to carry out external calibration daily to avoid measurement errors of any kind and to ensure high precision.

So, when choosing an equipment for the laboratory one of the most important issues to make clear is the necessary accuracy and the field of application. After making it clear what the minimal weighing limit of the scales should be and what types of substances should be weighed and under which conditions, the suitable type of the balances should be selected.

One more point to remember is that accuracy and precision of the balances are not synonyms and accurate not always means precise. Though accuracy is very important since it shows the correspondence to the real value, it is also vital for the laboratory scales to be precise (which means the measurements are repeatable), because it is much easier to adjust the balances in case of an error.

High accuracy is a feature that any customer expects from their weighing equipment. Depending on the function of the laboratory balance, the required accuracy levels may differ from the expectations of the user. There is no place for measurement errors in the lab since the tests and experiments must be carried out with high precision. Weighing is one of the most fundamental procedures performed at any medical or scientific laboratory. For many modern laboratory scales, precision is vital and they must additionally possess features such as averaging, control weighing, piece-counting, and percentage weighing that makine them indispensable devices for researchers.

Laboratory research is often performed using small weights as well as various ingredient mixtures and materials. Therefore, the laboratory balance must be able to offer the smallest readability with numerical precision to the required decimal digits. Each laboratory must determine the minimum requirements and capacity needed for their application as accuracy and readability is one of the influencing price factors with laboratory balances. Precision lab equipment should be protected from any possible harmful elements including dust, wind, and vibration. Certain laboratory balances and weighing platforms,, are equipped with various auxiliary enclosures to provide full dust, wind, and vibration protection for the device and the material being weighed.

A modern, digital laboratory balance allows you to switch between different measuring units as well as utilize connectivity through a PC or other devices. Connectivity allows the user to see readings in real time, the capability of keeping a record of weighings or experiment logs, as well as easy preparation for detailed reporting. Depending on the type of laboratory and its required equipment, the scales may feature components such as an internal calibration function and overload protection. These functions are designed not only for continuous accuracy, but to protect the units internal systems. If a laboratory operates in compliance with the ISO or NIST requirements, government regulations, and specific industry standards, the operator must exercise particular care and observe specific rules to guarantee the scales and balances operate as designed. Laboratory equipment requires periodic care and maintenance due to its high sensitivity and precision accuracy.

A laboratory without laboratory balances is hard to imagine. Laboratory balances are a very important tool for reproducing, checking and improving experiments. Depending on the laboratory and its specialization, special requirements for the laboratory balances to be used are defined. Thus, both heavy duty and microbalances are used as laboratory equipment in many laboratories worldwide. The term "laboratory balances" applies more not to a specific type of balances, but rather to the environment in which they are applied.

In order to find the right laboratory balances, the first thing to do is to define the experimental setup.

In this phase, the decision is made as to whether laboratory balances are used and what requirements they should meet. In the first step, the user gets a clear idea about the design of the laboratory balances. There is a wide variety here, presented by every conceivable option, from the bench scales, floor scales and hanging scales to individual load cells.

Once the design issue has been settled, the required accuracy and maximum load of the laboratory balance must be defined. These two parameters are directly related.

Especially when it goes about the measurement accuracy, some things have to be considered. Thus, the specified accuracies connected with such factors as e.g. working temperature range, platform size, application time and minimum weight.

Depending on the requirements, different measuring methods with their strong and weak points are used. The most widely used measuring method is the strain gauge method, but also the other measuring methods such as electromagnetic force compensation cells, piezoelectric force transducers, vibration side sensors and mechanical laboratory balances, e.g. spring scales can meet the requirements.

Here, the regulations, such as any ATEX approvals or the calibration requirement, must also be taken into account.

At this stage, the metrological possibilities and the connected with that financial expenses become clear. If there is no agreement here, the experimental set-up and the measuring technology used must be re-examined. If the user comes to an agreement, it may be proceeded further to the evaluation and processing of the measurement data.

For some applications, just the weight indication on the display of the laboratory balances is quite sufficient. These laboratory balances are standard and are very quickly available.

But even some of these laboratory balances also have special functions that are intended to facilitate the work for the user. Here, the data evaluation happened via the laboratory balances.

Especially in the international comparison, different measuring units must be brought to a common denominator. The laboratory balances can represent the measurement values in different units, e.g. g / lb / mg / grain / ct / uvm. represent. Some laboratory balances also offer the option of entering a freely adjustable conversion factor. This facilitates the work immensely and prevents conversion errors.

The determination of the grammage (g / m²) also belongs to this functional range and is often required by the laboratory in the textile industry.

A widely used function in the field of the laboratory scales is the animal weighing function. The problems with the animal weighing are the dynamic measuring tips, which are measured when the animal is active. The animal weighing function evaluates the measurements according to a certain algorithm so that the influence of the movements of the animal on the measurement results was minimized.

With this function, the weight can be stored as a 100% value in the laboratory balances. All the subsequent weighing actions are then set in a percentage ratio. With this function, the recipes for a certain final quantity can be mixed quickly and safely from many individual components.

With this function, the laboratory balances hold the highest measured value on the display. In fracture tests, a force that increases continuously is built up and then discharges abruptly when it breaks. With this function, the user has the opportunity to see the force required for the break on the display.

For fracture tests, however, the sampling rate should also be taken into account. The laboratory balances are designed for accurate results and not for achieving high sampling rates. For such applications, a force gauge should be tested. The scales have a sampling rate of about 10Hz, while a force measuring device can reach the sampling rates of up to 10kHz. Thus, the force curve can be better evaluated.

The laboratory balances are able to collect the measured values of the individual weighings and evaluate them for the user. The user can immediately see the information, such as the lowest or highest determined weight, the average weight and the standard deviation, on the laboratory balances, log the data as a printout or transfer them to a PC.

For the PC-independent logging, laboratory balances can be provided with a date and time module in order to be able to better allocate the measured data.

During many laboratory tests, however, special attention is paid to the collection of the raw data.

Most laboratory balances have an interface that allows data transfer to the PC.

This interface may be executed as e.g. RS-232, USB, LAN or W-LAN. The requirements for the laboratory balances depend on the already existing systems. Thus, also laboratory balances with an analogue signal 4-20mA or 0-10V are possible. The PC-independent data recording on internal data carriers can also be found in the laboratory balances.

A common problem that is often reported by different laboratories relates to the laboratory balances, which show no weight difference on the display when small or slow changes in weight take place. The problem is based on the fact that the laboratory balances record the collected values, evaluate them and then show them to the user on the display. Depending on the laboratory balance, small or slow weight changes can be declared in the evaluation as possible interference signals which the balances must neutralize. As a result, the user cannot follow this weight change. With the help of the laboratory balances with a higher resolution the problem can be counteracted. The second possibility is the laboratory balances with a zero tracking, which can be deactivated, as well as the function that can influence the evaluation, such, for example, as adjustable filters. Especially during the warm-up phase of the laboratory balances, the automatic zero tracking is used until the measuring electronics reaches the operating temperature.

Even if the laboratory balances can show a value on the display from the first resolution step, the weighing should be carried out through the minimum load of the respective laboratory balances in order to achieve the declared accuracy of the measurement. Depending on the application, some possible safety factors should be additionally used to ensure the accuracy of the process.

Due to the technical specifications, each model of the laboratory balances can be tested for the suitability for the respective test setup. If there are any doubts or open questions, our technicians will be glad to provide you with an expert advice and assistance.