Technical data

40 Theoretical and general applications www.westermo.com
Reducing Interference
In any system, electronic signals are always prone to interference. Analogue signals
tend to be more prone due to the fact that all points on the signal carry information-
i.e. amplitude and frequency. Small disturbance to the signal will cause the receiving
system to interpret the signal differently to that of the original transmitted signal and
give an incorrect output. Digital signals are less prone to interference as there are only
two basic states; high or low. However due to the interaction of the capacitance,
resistance and inductance of the cables used to carry the digital signals and the effects
of external noise, the information contained in the signals can be distorted until the
signal is unrecognisable.
Balanced Signals
Balanced signals are used to transfer pulse signals over long distances with differential
interfaces like RS-422/485 or W1.
When balanced protocols are used on twisted pair cable
the cross talk between the pairs is effectively cancelled
out by the oppositely induced fields caused by the cur-
rent flow.
This effect does not occur in unbalanced systems.
Isolation
In all data communications it is essential to galvanically isolate equipment and networks
from each other to prevent the propagation of transients and other forms of inter-
ference that can cause transmission errors or damage equipment.
There are several methods ensuring isolation for example relays, transformers,
isolation amplifiers and optocouplers. Incoming transients can also be removed using
protective components such as varistors, capacitors, RC filters and zener diodes.
Westermo use optocouplers for isolation in their receivers. Optocouplers provide
better performance than for example differential amplifiers. Transformers provide iso-
lation on the power source and varistors and zener diodes are used to suppress tran-
sients.
Fast balanced
communication
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