Other Dimensions: Build Your Own Cal Lab

November 1, 2004
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Controlling the environment is critical to successful in-house calibration.

Editor's note

This installment in a multipart series focuses on manufacturers doing their own calibration. The series looks at the reasons why a manufacturer might make this choice, as well as some of the considerations that must be taken into account when embarking on this course of action.

Where will a manufacturer, who has decided to bring calibration in house, actually perform the duties associated with that job? The answer to this question may seem obvious. Many manufacturers who need to answer this question might assume that an already existing inspection department, with some degree of air conditioning, will suffice. This answer may seem to be the most logical, until a close examination is made of the requirements and the realities of everyday work.

In dimensional measurement, temperature is the most important environmental consideration for a calibration facility. The basic requirement is to have a stable temperature at 68 F. The key word here is "stable." Many manufacturers start scheming how they'll get the temperature in their lab to where they want it only to discover there are wide fluctuations. They forget that people come and go, and if there is no air lock at the laboratory entry and exit point, the swoosh of air that accompanies every door opening will cause the temperature to rise or drop.

Another factor that contributes to an unstable environment is a window to the outside that allows the sun to shine in. This problem can be eliminated by using shades or blinds of course, but when people are stuck in a closed room for most of their working day, a shuttered window may not remain that way for long.

The biggest factor in maintaining the working environment of a calibration facility is the air conditioning equipment. The selection of the equipment is determined by the volume of air to be handled, the heat loads involved and how near to standard requirement the temperature will be held. If the lab has many computers, they will add to the heat load and air flow problems. The closer to the standard requirement the temperature will be held, the higher the capabilities must be, and ultimately the cost, of the equipment.

The details of what type of environment to create and how to go about that, is best sorted out by a specialist. A manufacturer moving calibration in house must have realistic requirements and have them spelled out. The National Conference of Standards Laboratories International can provide help and recommended practices in the form of technical papers that cover what is needed for calibration lab. These papers are available at nominal cost.

The lab environment is critical to calibration. An average temperature that is close to the standard is good, but not so if there are "hot spots" where the calibration is done. If nothing else, manufacturers should know that sticking a typical air conditioner in a window or a hole in the wall isn't enough except for all but the coarsest requirements.

Cleanliness is an important consideration in creating a calibration lab. In the best labs, shoe covers must be used when entering the facility so outside dust and dirt are not tracked into it. This may be more stringent than what most manufacturers do, but at minimum, there should be replaceable or washable doormats at the entrance to make it possible for those entering to clean the dirt from their shoes.

Because most manufacturers will locate their calibration lab inside a larger facility with production equipment, extra precautions may be needed to prevent the vibrations from punch presses, etc., from making the calibration processes unstable. Similarly, if calibration devices require a clean, stable electrical supply, it may be necessary to isolate the calibration lab from the plant electrical supply. And if air-operated instruments or a coordinate measuring machine with air bearings are being used, the plant air supply may need to be cleaned up or better filtration may need to be installed before that air is used in the lab.

Decent illumination and uncluttered work areas in a lab are also requirements to correctly calibrate. In ISO 17025, the standard that covers calibration, similar requirements to those I have noted must be taken into account when evaluating current or future calibration operations. This is particularly important if the manufacturer intends to obtain accreditation for his lab.

Now that we've covered the playpen, it's time to consider who will be in it. The next column in this series will deal with this topic.

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