APPENDIX A
pg. 41
1212 & 1212P Manual - Sep 2019
APPENDIX A
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 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.
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.
Radiated paths are created when the controller circuitry is immersed in an external field. This
coupling can be reduced by placing the controller as far as possible from the noise source or by
enclosing the controller in a metal box. Some Curtis controllers are enclosed by a heatsink that also
provides shielding around the controller circuitry, while others are partially shielded or unshielded.
