Contents | 11
Electromagnetic Compatibility (EMC)
Read and follow the recommendations in this section to avoid perfor-
mance variations or damage to the internal circuits of this equipment
when installed in harsh electrical environments.
The various congurations of the Model 888 should not produce, or fall victim to, elec-
tromagnetic disturbances as specied in the European Union’s EMC Directive. Strict
compliance to the EMC Directive requires that certain installation techniques and wiring
practices are used to prevent or minimize erratic behavior of the Analyzer or its electronic
neighbors. Below are examples of the techniques and wiring practices to be followed.
In meeting the EMC requirements , the various Analyzer congurations described in this
manual rely heavily on the use of metallic shielded cables used to connect to the custom-
er’s equipment and power. Foil and braid shielded I/O and DC power cables are recom-
mended for use in otherwise unprotected situations. In addition, hard conduit, exible
conduit, and armor around non-shielded wiring also provides excellent control of radio
frequency disturbances. However, use of these shielding techniques is effective only
when the shielding element is connected to the equipment chassis/earth ground at both
ends of the cable run. This may cause ground loop problems in some cases. These should
be treated on a case-by-case basis. Disconnecting one shield ground may not provide suf-
cient protection depending on the electronic environment. Connecting one shield ground
via a 0.1 microfarad ceramic capacitor is a technique allowing high frequency shield
bonding while avoiding the AC-ground metal connection. In the case of shielded cables
the drain wire or braid connection must be kept short. A two-inch connection distance
between the shield’s end and the nearest grounded chassis point, ground bar or terminal
is highly recommended. An even greater degree of shield performance can be achieved
by using metallic glands for shielded cable entry into metal enclosures. Expose enough of
the braid/foil/drain where it passes through the gland so that the shield materials can be
wrapped backwards onto the cable jacket and captured inside the gland, and tightened up
against the metal interior.
Inductive loads connected to the low voltage “Alarm Contacts” are not recommended.
However, if this becomes a necessity, adhere to proper techniques and wiring practices.
Install an appropriate transient voltage suppression device (low voltage MOV, “Tran-
szorb,” or R/C) as close as possible to the inductive device to reduce the generation of
transients. Do not run this type of signal wiring along with other I/O or DC in the same
shielded cable. Inductive load wiring must be separated from other circuits in conduit by
using an additional cable shield on the offending cable.
In general, for optimum protection against high frequency transients and other distur-
bances, do not allow installation of this Analyzer where its unshielded I/O and DC cir-
cuits are physically mixed with AC mains or any other circuit that could induce transients
into the Analyzer or the overall system. Examples of electrical events and devices known
for the generation of harmful electromagnetic disturbances include motors, capacitor
bank switching, storm related transients, RF welding equipment, static, and walkie-talk-
ies.
!
CAUTION
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