Partlow MIC 6000, Инструкция по установке, монтажу и эксплуатации., Страница: 9 / 82

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2. If possible, eliminate mechanical contact relay(s) and replace with solid state relays. If a
mechanical relay being powered by an instrument output device cannot be replaced, a
solid state relay can be used to isolate the instrument.
3. A separate isolation transformer to feed only instrumentation should be considered. The
transformer can isolate the instrument from noise found on the AC power input.
4. If the instrument is being installed on existing equipment, the wiring in the area should be
checked to insure that good wiring practicies have been followed.
2.5.1.2 AC POWER WIRING
Earth Ground
The instrument includes noise suppression components that require an earth ground connec-
tion to function. To verify that a good earth ground is being attached, make a resistance
check from the instrument chassis to the nearest metal water pipe or proven earth ground.
This reading should not exceed 100 ohms.
Neutral (For 115VAC)
It is good practice to assure that the AC neutral is at or near ground potential. To verify this, a
voltmeter check between neutral and ground should be done. On the AC range, the reading
should not be more than 50 millivolts. If it is greater than this amount, the secondary of this
AC transformer supplying the instrument should be checked by an electrician. A proper
neutral will help ensure maximum performance from the instrument.
2.5.1.3 WIRE ISOLATION
Four voltage levels of input and output wiring may be used with the unit:
* Analog input or output (i.e. thermocouple, RTD, VDC, mVDC or mADC)
* SPST Relays
* SSR driver outputs
* AC power
The only wires that should be run together are those of the same category. If they need to
be run parallel with any of the other lines, maintain a minimum 6 inch space between the
wires. If wires must cross each other, do so at 90 degrees. This will minimize the contact with
each other and reduces "cross talk".
"Cross talk" is due to the EMF (Electro Magnetic Flux)
emitted by a wire as current passes through it. This EMF can be picked up by other wires
running in the same bundle or conduit.
In applications where a High Voltage Transformer is used, (i.e. ignition systems) the secon-
dary of the transformer should be isolated from all other cables.
This instrument has been designed to operate in noisy environments, however, in some cases
even with proper wiring it may be necessary to suppress the noise at its source.
2.5.1.4 USE OF SHIELDED CABLE
Shielded cable helps eliminate electrical noise being induced on the wires. All analog signals
should be run with shielded cable. Connection lead length should be kept as short as
possible, keeping the wires protected by the shielding. The shield should be grounded at one
end only. The preferred grounding location is at the sensor, transmitter or transducer.