Appendix A Vehicle Design Considerations - Curtis 1212 Manual

Curtis 1212 Manual
VEHICLE DESIGN CONSIDERATIONS
REGARDING 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 motor controllers.
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). Contactor drivers and the motor drive output from Curtis controllers
can contribute to RF emissions. Both types of output are pulse width modulated
square waves with fast rise and fall times that are rich in harmonics. (Note:
contactor drivers that are not modulated will not contribute to emissions.)
The impact of these switching waveforms can be minimized by making the
wires from the controller to the contactor or motor as short as possible and by
placing the wires near each other (bundle contactor wires with Coil Return;
bundle motor wires separately).
For applications requiring very low emissions, the solution may involve
enclosing the controller, interconnect wires, contactors, and motor together in
one shielded box. Emissions can also couple to battery supply leads and throttle
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 potenti-ometer. 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.
Curtis controllers include bypass capacitors on the printed circuit board's
throttle wires 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.
APPENDIX A: EMC DESIGN CONSIDERATIONS
APPENDIX A
A-1