Internal vs External Analytical Balance Calibration

The Kern ABJ analytical balance features automatic calibration. The companion ABS balance is calibrated externally.
The Kern ABJ analytical balance features automatic calibration. The companion ABS balance is calibrated externally.

Calibration is a procedure intimately associated with analytical balances.  Calibration determines the relationship between the displayed value and true mass by comparison with a known mass.  In other words, calibration determines the accuracy of an analytical balance or precision scale.

Suppliers of analytical balances and precision scales such as Tovatech have sources that provide calibration services and certificates for newly purchased equipment.  Good laboratory practices, good manufacturing practices as well as conformance to several published regulations call for regular recalibration of these instruments and adjusting them if required.  To accommodate this manufacturers such as Kern offer analytical balances and precision scales with automatic internal calibration and adjustment (if needed) or external calibration and manual adjustment.

In the former case, the scale’s accuracy is set with an internal motor-driven adjusting weight, in the latter accurately calibrated external weights are placed on the equipment’s weighing pan and compared to the instrument’s readout.  These weights must also be recalibrated on a regular basis.

Internal or External Calibration, Which to Choose?

Just as drivers may argue the benefits of an automatic transmission vs. a stick shift, cases can be made for internal or external calibration.

High-end analytical balances such as the Kern ABT offered by Tovatech provide automatic internal calibration under several scenarios in order to maintain their accuracy.  These occur 4 hours after the previous calibration, when there is a fluctuation in temperature of 0.5oC (0.9oF), when the balance is switched from standby to weighing mode and the first and second conditions are met, and if the balance was disconnected from its power source.  If the analytical balance is out of spec, an automatic internal adjustment is made.

The conditions under which the Kern ABT and other Kern analytical balances such as the AEJ and ABJ automatically recalibrate also apply to externally calibrated instruments such as Kern’s ABS and ALS-A models .  Conditions include excessive vibration, temperature fluctuations, power failures, moving the balance to another location and time in use.   Test weights are used for this process, and if an adjustment is required it is made manually by following the built-in adjustment program.

Externally calibrated scales are generally less costly, and if a laboratory uses several of the same models of analytical balances, checking the accuracy of each is a relatively simple series of the same steps.  This can be performed quickly but requires that calibration is performed in conformance with changing operating conditions.  In other words manual recalibration might be on ongoing process diverting personnel attention from other tasks in the facility. Outside recalibration and adjustment services are available for this activity, but at a cost.

The higher cost of premium analytical balances such as the Kern ABT is justified for operations where precision weighing is a key operating goal.  The cost is somewhat offset by the fact that external calibration weights are not required. When calibration and adjustment is automatic, it does not divert staff from other responsibilities.

Regardless of whether balances are automatically or manually calibrated, record keeping is essential if your lab follows GLP/ISO practices.

Tovatech’s weighing specialists are ready to help you determine whether an internally or externally calibrated analytical balance is best suited to your operations.

What do you consider the advantages and disadvantages of automatic and manual calibration to be? What are analytical balances used for in your operation?

About Rachel Kohn

So how did an MIT Ph.D. end up selling refrigerators? When I figured out that a lot more scientists buy lab refrigerators than innovative leading-edge instruments. I hope that my many years of lab experience will help you find the right equipment for your work. Before co-founding Tovatech I worked in business development and project management at Smiths Detection, Photon-X, Cardinal Health, and Hoechst Celanese. And before that I spent 12 years as an R&D chemist at Hoechst Celanese and Aventis working on advanced drug delivery systems, polymer films and membranes, optical disks, and polysaccharides. Some day, eventually, I’ll make enough money to develop an innovative technology that will change the world. Read More