2005 Articles

Does your process generate a charge? There’s only one way to know for sure.

One question often asked is: Does my process generate an electrostatic charge and if so, how much? If the ESD program manager is looking for a simple yes or no, the answer may be disappointing. If, however, the program manager is making an argument for the complexity of ESD, then the answer proves the point.

Static control would be much easier if a yes or no question led to a successful ESD control program. But oversimplification often creates more problems than it solves. In ESD control situations this is more the rule than the exception. While ESDA standards such as ANSI/ESD S20.20-1999 provide guidance and starting points, each process and facility is unique. Therefore successful ESD control relies not on guessing but measuring.

Why take the time to measure your processes or materials? Measurements will aid in ESD control from the outset of a control program through to program maintenance.

First, measurement allows you to define problems accurately. From an ESD perspective, most environments are unique. What might cause an ESD problem in one environment may not cause one in another. Measurement helps identify whether or not a problem exists in your environment. Those measurements then provide concrete documentation for obtaining the financial and personnel resources needed to solve the problem.

You can arrive at more accurate solutions through measurement. For example, if the insulators in your environment are not producing electrostatic fields, why purchase ionizers to solve a problem that does not exist? Once measurement has allowed you to accurately identify the problem, you can prioritize those areas that require the most attention and select the appropriate solutions. The more specific your knowledge of the problem, the more successful your solution will be. For example, knowing that a material has a resistance of 10⁶-10⁹ helps prevent confusion that can occur with the imprecise use of terms such as conductive or dissipative.

Once ESD control measures have been selected and put in place, you can assess progress and results through measurements. If your solution reduces electrostatic potentials on personnel from 1,000 to 50 V, you know that the solution has been effective and you can check regularly to ensure that the program continues to work.

Where to start. What do you measure in your facility? Generally, measure those processes and materials that you suspect of generating electrostatic potentials or charge: personnel moving in the area, conveyor systems, monitors, insulators, carts, etc. After ESD control processes and materials have been selected, they should also be measured to ensure the items function properly and continue to do so.

Measurement equipment. Generally, two types of measurements should be considered: electrostatic fields or potentials and resistance or resistivity. Some relatively inexpensive equipment options are resistivity meters, resistance test kits and electrostatic field meters. For process and facility evaluation, your primary interest is an indication of whether a material or process generates high or low levels of electrostatic charge. Frequently, you simply want an indication of whether a material is insulative or conductive.

For material evaluation and qualification you may need to conduct laboratory level tests, which may require more precise instrumentation.

ESD control does not often fit into a simple yes or no framework. When observations and intuition are supported with data, surprises and guesswork can be eliminated. By making a practice of measuring, implemented ESD control measures are more likely to be effective – and successful.

This column is a regular contribution of the ESD Association, Rome, NY; (315) 339-6937; email: info@esda.org.

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