LAB Scales / Laboratory Scales

A laboratory without laboratory balances is hardly imaginable. Laboratory balances are a very important tool to reproduce, check and improve experiments. Very different tests and series of experiments can be carried out in the laboratory. The accents vary, depending on whether it is assigned to the product development or quality assurance in the pharmaceutical industry or in special machine construction. Therefore, heavy-duty scales as well as precision scales and fine balances are used as laboratory balances. The term "laboratory balances" is thus not limited to a specific type of the balances, but rather describes the environment in which the balances operate.
To find the right laboratory balances, the first step is to clarify for which applications the balances are to be used. Already at this stage, it becomes clear whether separate laboratory balances are sufficient for all the measurements in the laboratory or whether it makes sense to purchase several balances with different functionality or design. Once the requirements for the laboratory balances have been determined for all the measurement tasks, in most cases, the user can then decide on the design of the laboratory balances. From the bench scales as compact or platform scales, floor scales and suspended scales up to individual load cells with separate display unit, there are many variants in different sizes and with different capacities. The load capacity, i.e. the maximum load, the resolution and the required accuracy are more directly related to the scales of one series. Because the load cell signals for the applied load can only differentiate within a limited range, the number of the display options is limited. Laboratory balances with 3,000 divisions have a resolution of 1 g at a maximum load of 3 kg and 20 g at a maximum load of 60 kg.

In many laboratories special regulations have to be considered. These can be, for example, hygiene regulations, specifications for the use of equipment in potentially explosive atmospheres, but also specifications for verification or calibration. On the one hand, the specifications serve to protect life and health and on the other hand – to ensure the accuracy of the measured values.

Depending on the specific requirements to the laboratory balances, different measuring principles, which have both strong and weak points, can be used. Most balances work with strain gauges (DMS), but also other measuring methods such as electromagnetic force compensation cells, piezoelectric force transducers, vibrating side sensors as well as mechanical measuring principles e.g. of spring balances can be suitable for the special requirements. If the operating conditions of your laboratory balances deviate greatly from the usual values, for example if the measurements are made under very high or very low temperatures, the choice is limited. Special solutions must be developed in this case, if necessary. The financial costs depend mainly on the metrological possibilities and the possibility of application with standard or special components. If no solution can be implemented with the intended measuring principle, the test setup and the measuring technique used must be re-examined.

The following criteria should be taken into account when preselecting the laboratory balances:

Accuracy: For certain experiments, very small quantities often have to be weighed in on the laboratory balances or very small differences have to be measured reliably with the laboratory balances. Depending on the effects of the incorrect measured values, safety factors are defined for many areas of application in order to minimize the measuring errors and to ensure that the values are sufficiently correct.

Minimum load: For verified balances, the minimum load refers to the lowest weight the correctness of which is checked during the official monitoring. This minimum load is also indicated on the type label of the verified laboratory balances. Even though the balances can show a value on the display from the first resolution step onwards, only the weighing values above the minimum load may be used. This is the only way to ensure that the declared measuring accuracy is achieved.

Minimum sample quantity or minimum weight: The minimum sample quantity can be higher than the minimum load of the verified laboratory balances. For some purposes, for example when weighing the ingredients for pharmaceuticals, very high accuracy is required. For pharmaceutical ingredients, for example, the deviation should not exceed one percent. This means that for weighing 1 g of active ingredient, the laboratory balance used should have the accuracy of 0.01 g. If the desired masses can no longer be weighed directly, according to the recommendations of the DAC/NRF these are the masses less than 0.020 g, the concentrates can be used or a higher quantity of the total formulation can be selected.

Due to the technical specifications, each laboratory balances can be tested for suitability for the respective test setup. If your requirements are so special, that the information in the specifications is not sufficient or that you need special adaptations, please contact us. Our technicians will be happy to provide you with an expert advice.

For some applications, just the weight indication on the display of the laboratory balances is completely sufficient. For many applications, however, it is necessary to store and evaluate the measured data. In addition to the storage and transmission options, many laboratory balances also have additional functions that make the user's work easier. For this purpose, special calculation functions are stored in the laboratory balances, which can be called up via the control panel.

Data storage and data transmission: Most laboratory balances already have an interface as standard, which enables data transfer to a PC. This interface can be designed as, for example, RS-232, USB, LAN or W-LAN. If the interface of the balances is not compatible with the data transfer system already existing in the laboratory, an additional interface can be optionally installed on some models. The RS-232 interface can also be connected to the USB port of the PC using an additional adapter. In some cases, direct data transfer to a PC at the location of the laboratory balances is not possible or not desired. In this case, the data can be stored on an attached data carrier and later read out to the PC at another workstation. Such data carriers are available, for example, to match the RS-232 and the often installed USB interfaces.

For special experiments where the measured data are to be further processed as an analog signal, the laboratory balances can be equipped with an analog interface with output signals of 4 to 20 mA or 0 to 10 V.

Different units: In international trade and for special applications, the units of measurement are used that differ from the SI unit gram. For these cases, the values can either be converted or the laboratory balances in which a conversion function is already integrated can be used. For this purpose, one simply selects the required unit from different units, such as g / lb / mg / grain / ct /…, in the function menu of the balances. Some laboratory balances additionally offer the possibility to enter a freely adjustable conversion factor. The device-internal conversion of the values into the required unit makes work easier and prevents conversion and transmission errors.
Also the unit gram per square meter for weight per unit area can be selected among the units of measurement. The weight per unit area is often required in the laboratories in the textile industry. The sample must be cut to the correct size with a sample cutter.

Animal weighing function: In research laboratories with movable measuring material the animal weighing function is often used. The measured values, which fluctuate in the case of the living animals and other unstable measuring goods because of the movement, are evaluated with a specific algorithm. After a short evaluation time a stable measured value is displayed.

Percent weighing function: For this function, a reference weight can be stored as a 100% value in the laboratory balances. All subsequent weighings are then compared with the reference weight. This allows mixing many individual components for certain recipes quickly and reliably in order to reach a specific final quantity.

PEAK Hold function: With the help of the suspended scales that can be loaded in tension, force measurements can also be carried out in the laboratory. Due to the PEAK Hold function, the laboratory balances record the highest measured value on the display. In tensile and fracture tests, a force is built up which increases continuously, drops from a certain range, depending on the material, and then suddenly decreases when the sample is destroyed. However, the highest force remains in the display as an additional indication value. For such tests the sampling rate should be considered. The laboratory balances are usually designed for accurate measurement results and not for achieving high sampling rates, i.e. measurements in close succession. For such material tests, the use of a force gauge should be preferred for a better evaluation of the force curve. The laboratory balances have a sampling rate of about 10 Hz, whereas a force gauge can achieve sampling rates of up to 10,000 Hz.

Statistic function: The laboratory balances with statistic function are able to collect the measured values of the individual weighings and evaluate them for the user. Information such as the lowest or highest determined weight, the average weight and the standard deviation can be immediately viewed by the user on the laboratory balances and the data can be logged as a printout or transferred to a PC.

Time / Date function: In order to link the measured data with date and time already in the laboratory balance, a date and time module is built into many balances. This means that even if there is a time delay in the transmission of measurement data, the date and time of the measurement is assigned to each value.

Automatic zero tracking: A common problem is that the balances that do not show any weight difference on the display when small or slow weight changes occur. The problem is often due to the fact that the scales record and evaluate the values and only then show them to the user on the display. Small or slow weight changes can be classified by the laboratory balances as possible interfering signals in the evaluation, which is why they are not shown as weight. Then the user cannot follow this weight change. The laboratory balances with a higher resolution can often solve this problem. Another possibility is the laboratory balances with zero tracking, which can be deactivated. There are also some balances where adjustable filters can be used to influence the evaluation of the measurement results.

For many manufacturing processes it is advantageous if necessary tests of raw material or product quantities can be standardized and automated. The laboratory balances with an interface for data transmission can also be used for automated series of measurements in the product manufacturing. The measured data are transmitted with date and time as soon as the weighing result is stable and can be stored and evaluated and assigned to the respective batch at any time .

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

Laboratory research is often performed using small weights as well as various ingredient mixtures and materials. Therefore, the lab scales 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, since accuracy and readability are among the influencing price factors with the laboratory scales. Precision lab equipment should be protected from any possible harmful elements including dust, wind and vibration. Certain laboratory scales and weighing platforms are equipped with various auxiliary enclosures to provide full dust, wind, and vibration protection for the device and material being weighed.

Modern laboratory scales allow 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 lab 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 lab scales and balances operate as designed. Laboratory equipment requires periodic care and maintenance due to its high sensitivity and precision accuracy.

When it goes about a 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 scales applied may also differ. In general, the laboratory scales may be analytical (with the highest precision class 1, 2), technical, microbalances, top loading weighung scales 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 scales 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 laboratory scales and balances are mostly used for especially precise measurements, where not only gram / pounds, but hundreds of a gram/lbs 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 scales and 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 lab scales 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 laboratory scales and 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 / lab 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 scales / lab scales 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.

Laboratory Scales with an Interface to an ERP system (e.g. SAP)
The direct transfer of weighing data from the electronic laboratory scales to the company's ERP system offers many advantages. It is considerably faster than entering data via the keyboard and less error-prone. The computer on which the ERP system runs does not have to be in the immediate vicinity of the scales. One of the basic requirements for direct transmission is that the laboratory scales send the weighing results in electronic form and that the ERP software can receive and correctly understand this data. The laboratory scales must therefore have an interface for sending the weighing data. RS232 and USB interfaces are widely used for the balances. Interfaces for Ethernet, Wifi or Bluetooth are rarely built into the balances as standard. However, some types of the laboratory scales can be equipped with one of these interfaces in addition to or instead of the RS232 interface at the customer's request. The existing or new balances with an RS232 interface can also be integrated into a network via an RS232/Ethernet interface converter or send the data wirelessly to mobile devices or PCs with Bluetooth with the help of the RS232/Bluetooth adapter.

However, to transmit the weight from the laboratory scales to a specific location in the ERP application, it is not sufficient to connect the balances and the computer via the interfaces. In order to have the sent data inserted at the active location instead of a keyboard entry, additional software is usually required. This can be integrated into an additional module of the ERP programme or be a separate software for integrating the balances that runs in the background. These software solutions are used, for example, to adjust the interface parameters such as bit rate and parity for the connected laboratory scales. Despite the same interface type and the same interface parameters, the data can be sent in different formats, as there is no generally binding communication standard for this. Therefore, some of the solutions only work for the balances that send the data in the same format; the others can work with different data formats. Some software solutions for connecting the balances make it possible for one computer to receive the data from several balances in parallel and process them.

Legal-for-trade / verified laboratory scales
For some applications, it is specified that legal-for-trade laboratory scales must be used for weighing. In principle, the verification of the measuring instruments always serves to protect the consumer. In trade, it is primarily a matter of ensuring that prices can be correctly determined when buying or selling products or materials. No matter whether food, spices, precious metals or something else is being sold, if the price depends directly on the weight, it must be weighed with the verified balances. But verification is also mandatory for other uses. For example, legal metrology applies to all laboratory scales used in pharmacies or other places to weigh the ingredients of mixed medicines. Even when masses have to be determined in medical and pharmaceutical laboratories for qualitative analyses, the laboratory scales used for this purpose must be verified. Independently of this, the verified balances must also be used for weighing when the weights are determined for legal opinions or in connection with the implementation of the legal regulations. Whether the verified laboratory scales is required for a specific application is determined by the laws and regulations of the states. In the case of doubt, it helps to consult the competent verification authority. If there is an obligation to use the verified balances, the user must also register these verifiable or already verified balances with the local verification authority and apply there 10 weeks before the end of the calendar year in which the verification period ends for an appointment for the first or renewed verification by the verification officials.

In order for the laboratory scales to be verified, it must meet certain requirements. For the scales of a certain design that have been tested and confirmed to meet the requirements, the manufacturer may issue a corresponding declaration of conformity. In addition, the manufacturer may affix the CE mark and the special marking for legal-for-trade measuring instruments to the scales. Although these legal-for-trade scales must be registered with the local weights and measures office, they are considered legal-for-trade until the end of the verification period. With any gravity-dependent scale, care must also be taken to ensure that the setting matches the gravity of the place of installation. Since legal-for-trade and verified scales may not be adjusted subsequently, the region for which the verification is valid is noted. The higher the accuracy class of the laboratory scales, the smaller the spatial area of validity for which the verification applies. In the case of the legal-for-trade or verified laboratory scales of accuracy class M III, for example, the verification is valid for any place of installation in the Federal Republic of Germany; though, in the case of the balances of accuracy class II, for example, it is only valid within one federal state. The laboratory scales of accuracy class II verified for the Hamburg location may therefore not be used in Frankfurt or Nuremberg without further ado. For this reason, the customer is usually asked at which location the verified balances are to be used. For digital scales of accuracy class M I with internal automatic calibration, this is usually not necessary. These scales have an internal test weight and perform an adjustment with this weight every time they are started and can thus adapt to the gravitational value of the place of installation without any intervention by the user.