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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.
2.2.1.4 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 the sensor, transmitter or transducer.
2.2.1.5 NOISE SUPPRESSION AT THE SOURCE
Usually when good wiring practices are followed no further noise protection is necessary.
Sometimes in severe electrical environments, the amount of noise is so great that it has to be
suppressed at the source. Many manufacturers of relays, contactors, etc. supply "surge
suppressors" which mount on the noise source.
For those devices that do not have surge suppressors supplied, RC (resistance-capacitance)
networks and/or MOV (metal oxide varistors) may be added.
Inductive Coils - MOV's are recommended for transient suppression in inductive coils con-
nected in parallel and as close a possible to the coil. See Figure 2-2. Additional protection
may be provided by adding an RC network across the MOV.
FIGURE 2-2
(Continued on next page)
0.5
mfd
1000V
220
ohms
115V 1/4W
230V 1W
A.C.
MOV
Inductive
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