Despatch MIC1462 Controller Manual User Manual

Page 13

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 the source.

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.

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
connected in parallel and as close as possible to the coil. See Figure 2-4. Additional
protection may be provided by adding an RC network across the MOV.

FIGURE 2-4