APPENDIX A – DESIGN CONSIDER ATIONS
APPENDIX A - Design Considerations
ELECTROMAGNETIC COMPATIBILITY (EMC)
Electromagnetic compatibility (EMC) encompasses two areas: emissions and immunity.
Emissions are radio frequency (RF) energy generated by a product. This energy has the potential
to interfere with communications systems such as radio, television, cellular phones, dispatching,
aircraft, etc. Immunity is the ability of a product to operate normally in the presence of RF energy.
EMC is ultimately a system design issue. Part of the EMC performance is designed into or
inherent in each component; another part is designed into or inherent in end product
characteristics such as shielding, wiring, and layout; and, finally, a portion is a function of the
interactions between all these parts. The design techniques presented below can enhance EMC
performance in products that use Curtis control products.
Emissions
Signals with high frequency content can produce significant emissions if connected to a large
enough radiating area (created by long wires spaced far apart). PWM drivers can contribute to
RF emissions. Pulse width modulated square waves with fast rise and fall times are rich in
harmonics. (Note: PWM drivers are 100% not contribute to emissions.) The impact of these
switching waveforms can be minimized by making the wires from the controller to the load as
short as possible and by placing the load drive and return wires near each other.
For applications requiring very low emissions, the solution may involve enclosing the system,
interconnect wires and loads together in one shielded box. Emissions can also couple to battery
supply leads and circuit wires outside the box, so ferrite beads near the controller may also be
required on these unshielded wires in some applications. It is best to keep the noisy signals as far
as possible from sensitive wires.
Immunity
Immunity to radiated electric fields can be improved either by reducing overall circuit sensitivity
or by keeping undesired signals away from this circuitry. The controller circuitry itself cannot be
made less sensitive, since it must accurately detect and process low level signals from sensors
such as the throttle potentiometer. Thus immunity is generally achieved by preventing the
external RF energy from coupling into sensitive circuitry. This RF energy can get into the
controller circuitry via conducted paths and radiated paths. Conducted paths are created by the
wires connected to the controller. These wires act as antennas and the amount of RF energy
coupled into them is generally proportional to their length. The RF voltages and currents
induced in each wire are applied to the controller pin to which the wire is connected.
The Curtis 1310 includes bypass capacitors on the printed circuit board’s sensitive input signals
to reduce the impact of this RF energy on the internal circuitry. In some applications, additional
filtering in the form of ferrite beads may also be required on various wires to achieve desired
performance levels. A full metal enclosure can also improve immunity by shielding the 1310
from outside RF energy.
1310 Vehicle Control System Users Manual Release Rev B Page 47 of 51
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