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.
Precautions & Procedures in Weighing On An Analytical Balance
Analytical measurements are highly important in a lab analysis. Most research and medical labs use electronic balances. There is always a margin of error during the weighing process which can be reduced, if not eliminated, through systematic preparation and by executing required lab practices.
Preparing the necessary tools for the weighing process like spatulas of the suitable size, forceps, weighing containers, pipettes, etc comprise the first phase of the process. Be cautious in choosing the weighing containers, their total weight should not exceed the maximum tolerable load of the balance. The sample to be weighed must be prepared and kept ready beforehand. Sometimes, the material needs to be ground or dried before it is weighed in the analytical balance. If kept in a refrigerator or heated, the sample must first reach the room temperature . Sometimes sample containers contain moisture. They must be opened only after they coincide with the temperature of the electronic balance to avoid condensation.
The second step in the weighing process is checking the balance. Lab personnel must always check the balance before undertaking any weighing activity. Failure to do so will result in wrong analytical data getting recorded. This in turn, will lower the accuracy of the measurements in the experiment. In labs where multiple personnel have access to the same balance, it becomes essential to check the balance carefully and thoroughly to avoid preventable errors. The calibration of the analytical balance must be checked together with the balance uncertainties and the balance environment.
The balance environment must be dust free, have a steady supply of electricity and should have minimum levels of air currents and vibrations. To keep the balance dust free, it is best to use camel hair brushes. It is also important to brush away test particles that settle down on the pan if the balance was used by the previous personnel. The balance should be recalibrated each time it is used, given some time to adjust to the recommended temperature for its correct operation.
It may be frustrating when some analytical balances do not attain equilibrium even after several hours of trying. A prudent way is to switch on the balance an hour before the scheduled weighing to equilibrate it. If the balance gets switched off, for example, during a power interruption, it is mandatory to recalibrate it and then start the weighing procedure all over again even if the balance displays only zeros.
The final step is weighing the substance on the analytical balance. The substance and its container must be removed from the pan immediately after weighing it because weight changes are possible due to the presence of the surrounding environment of carbon dioxide and water vapor. The tolerable load of the balance and the size and weight of the receiver/container should also be considered.
Precautions are highly crucial when lab personnel weigh liquids and toxic and hazardous solids. A mask must be worn to prevent chemical inhalation and gloves should be used to protect the hands.