Calibration is the process of comparing the measuring or output capabilities of a piece of equipment to a known standard. This allows for one of two basic actions that make sure that the equipment can be used effectively.

You can apply a correction factor to the instrument, much like “Kentucky Windage.”

Or you can actually adjust the machine to remove the gap between the reference standard and the item being calibrated.

In the common vernacular, calibration is thought to include adjustment as well. In reality, calibration and adjustment are two separate processes.

Calibration is most often done with measuring devices but can also be done with output devices.

Calibration can be a simple comparison, or a formal, documented process complete with statistical analysis. High end calibration services even trace back to extremely precise physical standards when generating their known value.

Some of these standards are arbitrary, such as how long a foot is or how heavy a pound is. Others, such as voltage, can be generated through a knowledge of physics and the right equipment. In either case, there is a hierarchy of standards that are used for calibration. The highest level standards are called primary standards and are developed using extremely sophisticated methods. Secondary standards trace back to the primary standards. The secondary standards are then used to create working standards that are used for actual calibration of test equipment.

Traceable calibration also includes some high-level statistics and multiple comparisons to be sure of the relationship between the test measurement and the known standard. For that reason, calibration of sophisticated equipment can be quite expensive.

Obviously, if the measuring device is determined to be too far from standard, it must also be adjusted and recalibrated.

The benefit of calibration is that your production processes will be done accurately and precisely. Imagine you are producing multimeters and want to test your equipment. For the accuracy you would need, you can’t simply test the meter using the voltage coming out of a wall socket. You would need a piece of equipment that generates a known voltage extremely accurately and test that output with the multimeter.

Those extremely sophisticated calibrations, however, are generally managed by a quality department. For the typical Lean practitioner or frontline employee, calibration is much simpler. Imagine you have a marking on a bench and a cutting device bolted 18 inches away to cut cable. You may produce a single piece cut to a precise length to use as a standard for comparison. Over time, the bolts may loosen up or the markings may be re-applied as they wear. Whenever there is a potential for a shift in a measuring device, it is good to calibrate against a known length.

You may also go beyond simple calibration and use gauge R&R to ensure precise measurements.

Calibration Intervals

Calibration intervals can be dictated by the manufacturer or can be managed by a calibration lab with a variable interval. The group measuring the device can calculate the drift of the machine and estimate how long the unit can be used until the next calibration.

Finally, some application may be subject to regulatory calibration requirements. This might apply to devices that are used in the testing of medical equipment, or similar applications.

Varying from any prescribed, time-based schedule depends upon the level of tolerance allowed and the risk of the device going out of tolerance. The reason for extending calibration intervals is obvious. Calibrations can be costly, and if you can reduce, safely, the number that you do, it saves significant cash.

But failure during a calibration can have a significant cost too. When a unit is calibrated and is found to have drifted outside acceptable limits, all measurements that came from that device since its last good calibration are suspect.

Lean and Calibration

Lean processes support good calibration practices. First off, efficient processes might reduce the number of devices that require calibration. If a company has 10 stations doing the same task, and gets a 10% productivity bump, one of those stations would no longer be needed.

With all the focus on processes in a Lean operation, it should come as no surprise that they probably would have a better-defined process to make sure equipment is calibrated on time.

Standardization and 5S act to reduce the potential causes of failure. If equipment is not misused, and it is kept clean and protected, it will be less likely to get knocked out of tolerance.