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The Weighing is always Inaccurate?

November 17, 2020

When the 0.01g lab electronic balance used, the weighing is always inaccurate? Do you have a good analysis of what caused it? In general, there are many reasons for the inaccurate weighing of samples in laboratory analysis, which can be roughly divided into several reasons such as analytical balance calibration, installation, environmental and physical factors of the sample, and improper operation.

1.The Analytical Balance Has not Been Calibrated Before Use

Before using an analytical balance, you must first confirm its correctness, otherwise the correctness of the balance cannot be guaranteed. Analytical balances should be calibrated regularly from the first use. Balances that are used continuously are calibrated approximately once a week. Calibration should be carried out in accordance with the specified procedures, and standard weights must be used for calibration, otherwise the calibration will not be effective.

2.Incorrect Installation of Analytical Balance

When installing the analytical balance, first choose a room with dust, moisture, shock, wind, sun, and constant temperature as the balance room. Secondly, the balance should be placed on a firm and reliable workbench and placed in an appropriate location. Before installing the balance, check the packing list to see if all parts are complete and in good condition, and carefully clean all parts of the balance. When installing, the balance should be assembled correctly according to the manual of the balance. After installation, check whether the installation of each part is normal, and then check whether the power supply voltage meets the requirements of the balance, and turn on the balance to check whether it is normal.

3.Environmental and Sample Physical Factors

In the process of weighing with an analytical balance, environmental and physical factors will interfere with the weighing results, such as temperature, sample volatilization, moisture absorption, magnetism, static electricity, etc.

The Influence of Temperature Changes on the Analytical Balance

If the displayed value drifts in one direction during the weighing process, it may be affected by temperature changes. If there is a difference in temperature between the sample and the surrounding environment, this temperature difference will cause airflow along the weighing container. The air flowing along the outside of the container produces an upward force, which leads to an error in the weighing result: the sample weighs lighter than the actual weight under the dynamic buoyancy. This effect will not stop until the temperature equilibrium is formed. After taking the sample out of the drying oven or refrigerator, wait until the temperature of the sample is consistent with the temperature of the laboratory or weighing room before weighing. The sample should be placed in a tare container with the smallest possible surface area, and tweezers should be used to pick and place the weighing container, instead of putting your hands in the weighing chamber.

The Influence of Sample Moisture Absorption or Volatilization Measurement Results

If the displayed value continues to drift in one direction during the weighing process, it may be a volatile or hygroscopic sample being measured. If the sample is highly hygroscopic, the weight will increase; if the measured sample is a volatile substance, the weight will decrease. For hygroscopic or volatile samples, use a narrow-necked container, cover or stopper the container, use a clean and dry weighing container, and keep the weighing pan free from dust, contaminants and water droplets.

The Influence of Static Electricity on the Sample or Container

If each weighing shows a different weighing result or the displayed value is unstable, or the repeatability of the weighing result is poor, it may be considered that the weighing container or the sample is electrostatically charged. The effect of static electricity will cause the weighing container to display a different weight each time it is weighed, and the repeatability of the result is very poor. Materials with high insulation, such as glass and plastic weighing containers, are prone to static electricity. This charging phenomenon is mainly caused by stirring or friction during the handling of the sample or container, and once it is charged, the charge will be removed very slowly. The chance of static electricity on the sample or container in dry air with a relative humidity of less than 40% increase. Usually, you can turn on the humidifier or properly adjust the air conditioning system to increase the air humidity, put the weighing container in a metal container for weighing, try to ground the analytical balance and other measures to remove or shield the static electricity on the weighing sample.

Improper User Operation Causes Inaccurate Weighing

Weigh blindly without checking before weighing. Before weighing, check whether the balance is normal, whether the balance is level, whether the weighing pan is clean, whether the display is reset to zero, etc. To solve this problem, it is necessary to operate strictly according to the requirements of the balance. Speaking of weighing, we have to mention the increment method and decrement method.

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