Electrostatic Discharge Sensitive (ESDS) Devices

Many electronic Line Replaceable Units (LRU's) on aircraft contain printed circuit boards containing components that are susceptible to damage from electrostatic discharges.  Such components are referred to as electrostatic discharge sensitive (ESDS) devices.  Decals installed on ESDS LRU's, indicate that special handling is required  

Static Electricity & Electrostatic Discharge

The most common conception of static electricity and its accompanying discharge, is the miniature lighting shock you receive when you touch a metal door handle having walked across a nylon carpet.  If the door handle is touched with a key first, the discharge will be seen but not felt.

The discharge occurs because different materials receive different levels of charge as materials are rubbed together or pulled apart.  The different charge levels create potential differences between the different materials, and when materials of different electrical potential are brought into close proximity with each other, a discharge occurs as the potentials equalise.

The different levels of charge with respect to cotton (the reference material) are shown on the following page, in what is known as the Triboelectric Series.

The further up or down, the greater the charge and hence the greater the discharge when the two materials are brought together.

Triboelectric Series

                Material

Air	Increasingly Positive
Human Hands
Asbestos
Rabbit Fur
Glass
Mica
Human Hands
Nylon
Wool
Fur
Lead
Silk
Aluminium
Paper
Cotton-----------------------------------------------	Increasingly Negative
Steel
Wood
Amber
Sealing Wax
Hard Rubber
Nickel Copper
Brass Silver
Gold Platinum
Sulphur
Acetate Rayon
Polyester
Celluloid
Orion
Saran
Polyurethane
Polyethylene
Polypropylene
PVC (vinyl)
Kelf (ctfe)
Silicon
Teflon