Alpha Communications TekTone NC377 Руководство по установке и эксплуатации - Страница 12

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A Word about ESD (Electrostatic Discharge)

What Is It?

Static electricity is a result of triboelectric charging of two

dissimilar non-conductive materials that are rubbed together,

such as rubbing your feet on a carpet on a cold winter day or in

a dry climate. The resulting charge is detected when you reach

out to touch a doorknob or some other metallic object. The

resulting discharge may only be startling or, in severe cases, it

may even be painful. The actual electrical charge is dependant

on the materials being rubbed together, humidity, the rate of

separation, and other factors.

What Can It Do?

While this effect may be disturbing to humans, the effect on

electronic equipment is often more serious, ranging from

operational disruption to actual component damage. These

effects result from the high voltages that may be developed.

The simple act of walking across a carpet may develop as

much as 30,000 volts, and changing a bed sheet may create a

charge of 100,000 volts or more. Such voltages readily cause

arcing (the spark that can be observed when you grab a

doorknob after walking across a carpet, etc.). The arcing is

evidence of the discharge path. Due to the high voltage

involved, the discharge current can jump to any nearby metallic

or non-metallic object. If the discharge is to or through an

electronic device, such as the nurse call system, the operation

of the device may be affected. If the discharge current passes

through internal components, these components may be

damaged or their operation degraded.

What Can We Do About It?

The manufacturer of the nurse call equipment has already taken

steps to protect the equipment from electrostatic discharge

(ESD) effects. Our peripheral equipment has been tested and

listed by ULR to withstand discharges of up to 30K volts.

However, since the cause is not in the equipment, but in the

environment, further measures are required of the installer and

the user to achieve complete protection.

Page 12 • IL871 NC377 Paging Interface Adapter Manual

What The Installer Can Do

In humid climates or in places where the relative humidity is

kept at 65% or greater, there will likely be few problems with

ESD. Where problems may occur the following measures can

be taken.

• Ground all exposed metal surfaces. Grounding should be to

a #16 gauge or larger conductor.

• Install nurse call system wiring in metal conduit. This

conduit may be used to ground panels.

• Use shielded cable for nurse call system station-to-station

wiring. The use of open conductors invites inductive cou-

pling of discharge currents, which can cause the same

problems as direct discharge currents.

• Ground your body before handling system components.

This can be done by using a wrist strap, or simply by

contacting a grounded metal surface. Use caution to avoid

hazardous voltages while grounded.

What The User Can Do

The most common generation of ESD in hospitals is due to

changing linen on hospital beds while the patient call cord or

pillow speaker is still connected to the nurse call system. The

following precautions will help. Remove the call cord or pillow

speaker from the bed before changing the linen. It will be

necessary for the nursing staff to discharge themselves by

contacting a grounded metal object before placing the call

cord or pillow speaker back on the bed; otherwise a spark will

jump to the nurse call equipment, causing the very damage

they are trying to avoid. To avoid a shock while discharging

static electricity on the body, hold a metal object, such as a

key, and use that object to contact the grounded surface.

This information is provided to make you aware of ESD

problems so that precautions may be taken to avoid damage

and disruption of system operation.