The analytical balance has been for many years an important tool in metrology, inspection, and production work in the chemical and pharmaceutical industries.  While its design has changed radically in the two centuries since its introduction, the operating and maintenance principles of the analytical balance have changed but little in that time.

    The analytical balance operates on the principle of torque, or the turning moment exerted by a tangential force acting at a distance from an axis of rotation.  Torque is calculated according to the formula

t = rF sin f

where t symbolizes torque, r the distance from the axis of rotation, F the applied force, and f the angle through which the force is applied.  For example, a force of 45 newtons moving through a 60-degree angle at a distance of five meters from the axis of rotation generates a torque of 194.85 newton-meters.

    In the case of the analytical balance, the mass of the object under examination exerts a force on a balance arm.  This force may be expressed as torque.  In a simple two-pan balance, counterweights are added to an identical pan placed at an equal but opposite distance  from the object until the balance is once again level; i.e., until the torque from the object being examined is negated by an equal and opposite torque.  In a single-pan design, the center of gravity of the balance arm may be changed by the movement of counterweights (known as riders) or chains along a vernier, thus negating the exerted torque.  Verniers are often equipped with a small magnifier for reading fine divisions, thus allowing a greater degree of discrimination.

    In the modern electronic analytical balance, which first made its appearance in the 1950’s, the countering torque is supplied by the magnetic field produced by an inductor.  In early models, the magnetic field was manually adjusted; however, in more recent models the magnetic field is controlled by an internal computer chip.  Readings are taken from an analog gauge or, in newer models, from a digital readout.

    To ensure accuracy in the readings obtained from the analytical balance, working balances are usually encased in a glass or plastic case to isolate the weighing pan or platform from air currents.  Some models may actually be hermetically sealed to permit the taking of readings in a vacuum or for chemical analyses such as the decomposition of a substance through combustion.  Nearly all modern analytical balances contain a leveling bubble and shock-absorbent pads on their bases to ensure that extraneous vibrations or an uneven surface do not affect readings.  Ideally, weighings are performed in a separate weighing room isolated from outside interference.  Of course, proper protocols for the use and care of the balance must be established to ensure accuracy in performing such analyses.

    Proper care of the balance and its attendant weights is essential.  All balances, regardless of their construction or operating principle, should be kept clean and inspected regularly for signs of wear.  Calibration is a matter of using an established standard to ensure that the scale "zeroes out" at the proper position or reading.  Weights, usually made of aluminum or stainless steel, must always be kept in their storage case when not in use, and should always be inspected for mechanical damage or corrosion which may affect the accuracy of readings.  Most manufacturers will periodically revalidate balances and weights to ensure conformity with manufacturing specifications.