Why Calibrate?

Some times the goal of an organization is to win wars and at other times the goal of an organization is to win business. Organizational goals are translated into manufacturing/ process requirements. Increasingly individuals and organizations depend on others to meet those requirements, and the tools they use may not all be compatible. The lack of compatibility reduces effectiveness and increases costs because good products are rejected and subjected to unnecessary handling and bad products are accepted leading to output that doesn’t meet the originally designed requirements. The result could be unnecessary loss of business (or worse) at greater than expected cost (see Table 1). Common standards of measurement are required to solve this problem. The process used to assure that thermometers and other measurement standards meet their requirements is called calibration. This involves regular periodic comparison with standards of higher accuracy. A credible unbroken chain of comparisons between thermometers of lower accuracy to thermometers of higher accuracy reaching all the way to national and international standards is called traceability. Those who are responsible for these comparisons are trained in metrology, the science of measurement.

Internationally, the common standard of measurement in temperature is called the Kelvin. A temperature scale known as the ITS-90 (International Temperature Scale of 1990) has been designed to facilitate traceable measurement to the Kelvin. Temperature standards called fixed-point cells and Standard Platinum Resistance Thermometers are used to realize this temperature scale. These devices are expensive and require a great deal of training to use properly. Less expensive easier to implement methods of calibration are used by secondary laboratories as they calibrate other thermometers which may be again used to calibrate other less expensive thermometers until finally they arrive in the hands of manufactures, service professionals or even consumers.

However, even with properly calibrated equipment there is another problem that if ignored will result in the same problems and costs associated with uncalibrated equipment. These thermometers once calibrated deteriorate over time and regular periodic comparison with standards of higher accuracy is necessary in order to maintain the required level of accuracy. Whether you work in a laboratory, plant or factory, following a program with a regular schedule of periodic calibration requires discipline and commitment but will prevent costly mistakes and failures due to inaccurate measurement.

Table 1. Annual cost of energy due to a 1 °F temperature error

Given
Process Fluid	Water
Flow Rate	100 gallons per minute
Control Temp	100 °F
Energy Cost	$0.11 per kW-Hr
Energy Cost	$14,021 per year

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