Analytical Balances

Analytical balance, as suggested by the name is an instrument used for analysis of mass. It determines the mass of the matter accurately and precisely. It is designed to measure small masses in milligram range, usually for experiment purposes. It is very sensitive so it can measure even the smallest of changes. It is basically used in chemical experiments, especially quantitative analysis. As we all know in quantitative analysis, accuracy is the key. In almost all analytical experiments, weighing the sample is always important for the reagents to be used in the preparation of the solution. The smallest of the masses have to be measured correctly otherwise large variations may be produced in the result. Now, as an analytical balance is so accurate, precise and sensitive, it is also pretty expensive. The most common type of analytical balance has a capacity of 100g and a sensitivity of 0.1mg. At All Scale Shop we have plenty of analytical balances and today we’d like to discuss how they work and what sets them apart from other balances.

Here’s how the parts of an analytical balance work:

Analytical Balances 

It consists of: An enclosed glass fitted case, a base plate, Beam Balance, and Stirrups. The working part, that is, the beam balance is actually enclosed in a glass case with doors. It is kept in such a way so that dust does not collect and so any air currents in the room do not affect the balance's operation. This enclosure is often called a draft shield.  The base plate is generally of black slate or black glass. The knife edges of the beam balance support the stirrups from which the pans are suspended. There is another knife edge in the middle (facing downwards) to support the beam balance on the bottom. When the balance is not in use and the pans are loading or unloading, the balance should be arrested.

Principle of working:

The working principle comes from the old arm balance. We used to balance both sides of the pan by

adding or taking out weights. The torque exerted by an unknown mass on one side of a pivot opposes the torque on the other side. The position of the pointer is noted. When it returns to the center, the torques are equal and weight can be calculated. Electronic analytical scales measure the force needed to counter the mass being measured rather than using actual masses. As such they must have calibration adjustments made to compensate for gravitational differences. They use an electromagnet to generate a force to counter the sample being measured and outputs the result by measuring the force needed to achieve balance. Such measurement device is called electromagnetic force restoration sensor.  Modern electronic laboratory balances work on the principle of magnetic force restoration. The force exerted by the object being weighed is lifted by an electromagnet. A detector measures the current required to oppose the downward motion of the weight in the magnetic field.

There are a few factors that affect an analytical balance:

Temperature: Slight change in temperature causes large variation in results. A constant temperature should be maintained while using an analytical balance. Also, the temperature should not be too hot or too cold as it may result in expansion or contraction.

Vibrations and air currents also tend to disturb the balance. It should be kept in a disturbance free environment to get error free results.

Always calibrate the equipment, it ensures an accurate reading. Some balances have internal calibration feature while labs conduct their own calibrations in some. It is recommended that you test your balance every few months and calibrate if needed.

If you have any questions about analytical scales, please contact us at All Scale Shop at 201-475-9184. A scales and balances expert will be happy to assist you.