LIKE MOST TECHNOLOGY, aircraft electrical components have changed dramatically over the past 20 years. With the invention of the transistor came the electronic revolution and miniaturization of electrical components. As transistors shrank even smaller, some became sensitive to the discharge of static electricity. Today we commonly find hundreds of transistors packaged together to form an integrated circuit or chip. The semiconductor material used to produce chips is often several millionths of an inch thick. Miniaturization has created electronic circuits which are extremely fast; however, they are also extremely vulnerable to static electricity. Components which are Electrostatic Discharge Sensitive are commonly referred to as ESDS parts. Since these components are becoming popular on all types of aircraft, maintenance technicians must be aware of the potential dangers from static electricity. What Is

By Thomas K. Eismin Professor of Aviation Technology Hangar 1 Purdue University Airport West Lafayette, IN 47906

mainly a function of the type of materials making contact, the amount of friction between the two and the relative humidity of the surrounding air. Static electricity can also be generated on some materials, such as plastic, by subjecting them to heat or pressure. Most everyone has experienced the production of a static charge while walking across a nylon carpet with plastic sole shoes. In this situation, approximately 35,000 volts can be generated if the relative humidity is 20% or less. Normally, you do not notice the static tf arge until you come in contact with another object, such as a door knob. At that time you are experiencing the discharge of the static electricity which was previously (before touching the door knob) stored on your body. This type of discharge will damage ESDS parts. The minimum perception level of a static electrical discharge is typically 3,000 volts. For a discharge to be seen

or heard it requires approximately 12,000 volts. The current produced during discharge is extremely low and produces only minor discomfort to humans; however, a static discharge of as little as 100 volts can damage certain electronic components. Figure 1 shows an example of the voltage generated by common materials found in a maintenance facility. How Are ESDS Components Identified?

In order to protect components from static electrical discharge you must first identify ESDS parts and then take the necessary precautions. Several labels have been designed to help identify sensitive components. The most common labels are shown in Figure 2. One or more of these labels should be placed on all ESDS parts. The label should be easily visible to anyone who might come in contact with the component. The identification labels must be used on components installed in the aircraft, as well as components found in shipping, storage or in a repair facility.

ElectrostaJc Discharge?

It is the discharge (movement of electrons) created when any material containing a static charge comes in contact with a material containing a different or neutral charge. A static charge is present when a material possesses an excess or deficiency of electrons. A neutral charge is present when a material possesses an equal number of electrons and protons. Any time two components of different static charge get close together, a static discharge will occur. Typically, a distance of 10mm or less is required to produce a discharge of static electricity which was generated due to normal maintenance activities.

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