Top Loading Balance vs Analytical Balance – What’s The Difference
Top loading balances are used for laboratory weighing where a margin of error up to 0.01 grams is acceptable. Analytical balances are more precise and are used in applications where the error margin is 0.0005 grams. The former type is used for knowing the mass of a sample during the process of pre-weighing while the latter helps determine the exact mass after through adjustments and calibrations. Semi-micro and micro balances are also analytical balances with much higher precision.
The sample is placed in a weighing container on the weighing pan of the top loading balance with no protection from air disturbances. The instrument is tared and set to zero grams. Lab personnel get a rough estimate of the weight of the test substance in a few seconds as the weighing isn’t precise. These devices function well when used in weighing substances up to a few kilograms.
Analytical balances need extra care when used. The device is placed in a glass or plastic chamber to protect it from air currents and vibrations. The sample to be weighed must be placed on the weighing pan only after the device is calibrated and displays only zeros. The doors of the chamber are closed. It is advised to record the weight within the first two seconds of its display. After the first two seconds, it is always possible for the weight to change because of environmental disturbances and the intrinsic nature of the test sample. After the substance is weighed and removed from the weighing pan, the doors of the chamber must be closed again and the display of the analytical balance checked. Lab personnel need to repeat the process if the display is not zero, at least twice or thrice to get only zeroes. The reason being any shift from zero shows that the weighing was not done properly and the exact mass of the test sample is not correct.
The top loading balance displays the mass of an object in the standard grams unit. They are usually manufactured along the same lines as industrial scales and are comparatively easy to use. They are digital and display the weight of the object up to three decimal places. Some have a conversion key feature that easily converts into other measurement units like milligrams, ounces and pounds. Laboratories, industries and educational establishments use them. They are compact and portable too. Some models can be battery-operated.
More precise weighing is achieved by analytical balances. They have specific instructions and professional recommendations for their operation. Only trained personnel should have access to them. They need to be regularly calibrated and their corresponding manual lists many tips for proper care and maintenance .
The choice of a top loading balance vs analytical balance depends on the degree of precision required by the experiment in determining the weight of samples. If decimal precision accuracy is not a major concern a top loading balance is appropriate while for those requirements where the test result will be adversely effected by even minor changes in the weight the analytical balance would be a better choice.
This article was written by Dr. Bob Sandor, a Director at Tovatech, a leading North American supplier of analytical balances. When not busy running his company, he explores his fascination with the many aspects of various scientific & industrial devices. For more information on this article visit the Tovatech site from any of the above links.
Understanding The Proper Use of Analytical Balance
Analytical balances are used in experiments where extremely accurate and precise weighing is required. Unlike usual scales that are not easily affected by environmental factors analytical balances are highly sensitive to environmental conditions including things like the strength of the local gravitational field, temperature, pressure, ventilation, relative humidity, air current, etc. They can be used for weighing milligram amounts of test samples as small as 0.01 mg or even smaller.
The entire weighing apparatus is enclosed in a chamber to get rid of environmental disturbance. This transparent chamber prevents potential loss of the sample and enables accurate weighing of substances in microgram quantities. It should be ensured that the sample is weighed at room temperature. A variance in temperature results in the formation of air currents that lessen the accuracy of the analytical balance. Various types of analytical balances are available depending on the requirements and needs of lab experiments. Weighing balances determine the weight and mass of test substances and samples. Top-loading balances are commonly found in all labs, research and development divisions and medical establishments. The loading capacity varies depending on the model type of the balance. They can be categorized as semi-analytical balances. Their readability is up to three decimal places or 0.001 grams. Analytical balances are very accurate and give better reading. They are also better suited to cope with a wide range of environmental conditions when steady readings are required. For a good idea about the features of the analytical balances installed in the lab, lab personnel must refer to the operating manual that has detailed instructions regarding the use of an analytical balance as well as guideline on its care and maintenance.
The auto calibration feature is now common for modern analytical balances. This should not be a point of concern for unsupported models because manual calibration is easy to perform and shouldn't take much time. Once the balance is calibrated using the available test weights, the test sample to be weighed should be put in the tared weighing container or weighing platform before closing the glass chamber. Liquids and pulverized samples must be handled carefully using a spatula and forceps. The weighing pan must be free of dust and other contaminants. Most importantly, the analytical balances must always display a stable zero reading before you begin the process of weighing.
Micro and ultra micro balances have a weighing span of six grams with a readability up to seven decimal places. Using these analytical balances is easy as they also offer a wide range of units in the display screen. Some of these are grains, ounces, kilograms, grams, newtons and pounds.
This article was written by Dr. Bob Sandor, a Director at Tovatech, a leading North American supplier of analytical balances. When not busy running his company, he explores his fascination with the many aspects of various scientific & industrial devices. For more information on this article visit the Tovatech site from any of the above links.
Analytical Balance – Factors Causing Its Uncertainty
Most scientific researches and laboratory tests require weighing, which is a critical task. However a level of measurement uncertainty is unavoidable. In fact, any weighing activity is subject to a degree of uncertainty. This can be neglected when dealing with large measures but takes on a great deal of importance when measuring minute amounts of substances that necessitate weighing as precise as 0.1 mg.
Does your work force you to weigh and measure specimen on a daily basis? How critical is the accuracy of the data for your research or industry? Do you realize the factors that can influence the results obtained from your analytical balance?
An Analytical Balance is a precision instrument that can measure small amounts of substances or samples with the highest accuracy. In spite of this you can still say there is a wide difference between ‘exact’ and ‘most exact’. To put it simply, any measurement is finally tentative. The scientific studies of measurements are based on a lot of theorizing under set parameters. Because of this, any weighing activity also has its uncertainties. To understand the working of an analytical balance, we also need to be aware of the factors that cause its uncertainty.
Comparison between data derived from different instruments is also hard to evaluate because the methods used in field operations differ from manufacturer specifications which are conducted under ‘ideal’ conditions.
There are also several other factors that can influence the accuracy of weighing results obtained. They can be collectively classified into three categories. The first group can come from the analytical balance itself. Different models of analytical balances have a varying degree of susceptibility in non-linearity, repeatability, temperature coefficient and sensitivity accuracy.
The second cluster causing a deviation can occur from actual environmental factors like humidity, temperature, air pressure, exposure to direct sunlight or heat radiation. Analytical Balances, especially the high-end ones are sensitive equipments. Even the whiff of a cold draft can get you pneumonic results!
The third and final group that can cause uncertainty in the results comes from accounting for human influence. The way the sample is loaded; technical errors during the weighing process etc. can all affect the weighed results. Even the accuracy of the calibration of the balance needs to be adjusted according to user-specific actual weighing capacity of the analytical balance in order to get the most precise results. Improved types normally support the option of calibrating the scale of an analytical balance at several predetermined capacities.
How is uncertainty accounted for in weighing results?
Does the obtained result from weighing actually represent the value measured? Although ‘uncertainty’ could mean a broad, general concept – the error from variation of results is generally minimized as ‘standard uncertainty’. ‘Standard Uncertainty’ is an estimation of standard deviation in obtained results owing to a combination of various factors. However, even the combined internal and external factors in ‘standard uncertainty’ holds good only when certain basic ‘ideal’ conditions are preserved. For example, the balance is positioned on a level surface and there are no unnatural variations in STP (Standard Temperature and Pressure).
This article was written by Anindita Biswas, a marketing professional with a streak of geek that just refuses to go away! At Tovatech she indulges in her passion for high precision engineering and scientific equipment. Tovatech is a leading North American supplier of analytical balances. For more information on this article visit the Tovatech site from any of the above links.