Weighing is an essential process for fulfilling quality requirements, so it’s vital to follow best practices. This Weighing Raw Materials SOP Template helps streamline and standardize your work.

Ensure the balance is in thermal and environmental equilibrium before taking any readings. Also, be sure that the weights don’t rub against each other.

Analytical balances

An analytical balance is a precision scale that provides precise measurements for weighing small samples or chemicals. It has a high level of accuracy and is used in various applications, such as research and compounding pharmaceuticals. The accuracy of an analytical laboratory balance depends on how it is set up and maintained. You should follow the guidelines for routine maintenance. You should also use a clean weighing surface. If liquids get inside the weighing mechanism, it can render it useless. To avoid this, tare the container before adding it to the balance.

Analytical balances are designed to detect extremely light increments, so it is important to keep them in an environment where they will not be disturbed. Ensure that it is in an area with little traffic, and avoid breezes or temperature changes. You can also buy anti-vibration tables to further stabilize the balance. Moreover, you should shield it from air currents coming from vents and burners.

Microbalances

When working with incredibly small samples, microbalances are the instrument of choice. Their unparalleled sensitivity allows for precise measurements in the nanogram range, making them essential to critical fields like pharmaceutical research and forensic science.

Due to their extreme sensitivity, micro balances are very susceptible to environmental influences like vibrations and temperature fluctuations. They should be placed in a hood or enclosure to shield them from drafts and other factors that can cause fluctuations. Many Adam Solis, Equinox and Luna models offer a draft shield to decrease interference and ensure accurate readings even when working with the smallest of samples.

It is also important to note that all electronic balances require a certain amount of time to stabilize before they are ready for use. The exact amount of time varies by model, but it is always recommended that you follow manufacturer instructions and allow enough time for the device to reach full functionality before performing any tasks.

Weighing by substitution

In weighing by substitution, the object of interest is replaced with known weights. These weights are added to one arm of the balance and removed from the other. The difference in the two arms’ weights gives the unknown object’s measurement. This method of weighing is popular in the pharmaceutical industry where high precision measurements are required.

The accuracy of a weighing system depends on several factors, including the design and placement of the load cells. A weighing system’s junction box should be waterproof to protect against moisture that can wick into each load cell and reduce the capacitance between the signal lines. Moisture entering the junction box can also affect weighing by increasing noise in the signal lines.

Vibration from process equipment or other sources can affect a weighing system’s accuracy by transmitting to the load cells and disturbing the strain gauges bonded at each point on the load cell. To prevent vibration, a weighing system should be isolated from the surrounding process equipment and the floor should be structurally sound to support the weight of the weigh vessel or platform.

Weighing by difference

In pharmaceutical, jewellery and manufacturing industries where weighing out potent substances or reagents demands accuracy down to the microgram, this method is ideal. It eliminates errors caused by the substance sticking to the container and ensures a clean, efficient and accurate weighing process.

A quality load cell (also known as a strain gauge or transducer) converts a mechanical force into an analog output signal, which is then converted by the controller to a digital weight measurement. A top-quality load cell has high sensitivity and minimal nonlinearity and hysteresis.

Vibration can affect the weighing accuracy by causing the load cells to bend. Using an isolation table or weighing boat for the weighing vessel will help reduce these effects and improve the overall performance of the weighing system.