Metek 920, Руководство оператора с основными требованиями по охране здоровья и безопасности

Страница: 14 / 278

xiv | Model 920 Multi-Gas Analyzer
Electromagnetic Compatibility (EMC)
Read and follow the recommendations in this section to avoid performance variations or dam-
age to the internal circuits of this equipment when installed in harsh electrical environments.
The various configurations of the Model 920 Multi-Gas Analyzer should not produce, or fall
victim to, electromagnetic disturbances as specified in the European Union’s EMC Directive
(if applicable to your application). 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 prac-
tices to be followed.
In meeting the EMC requirements, the various Analyzer configurations described in this manual
rely heavily on the use of metallic shielded cables used to connect to the customer’s equipment
and power. Foil and braid shielded I/O and DC power cables are recommended for use in other-
wise unprotected situations. In addition, hard conduit, flexible 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 equip-
ment 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 sufficient protection depending on the electronic environment. Connecting one shield
ground via a 0.1 microfarad ceramic capacitor is a technique allowing high frequency shield bond-
ing 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, “Transzorb,” 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 disturbances, do
not allow installation of this Analyzer where its unshielded I/O and DC circuits 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-talkies.
!
CAUTION