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Electromagnetic compatibility (EMC)
EMI SUSCEPTIBILITY - The governor system can be adversely affected by large inter- fering
signals that are conducted through the cabling or through direct radiation into the control circuits.
All DWC-2000 speed control units contain filters and shielding designed to protect the units
sensitive circuits from moderate external interfering sources.
Although it is difficult to predict levels of interference, applications that include magnetos, solid state
ignition systems, radio transmitters, voltage regulators or battery chargers should be considered
suspect as possible interfering sources.
If it is suspected that external fields, either those that are radiated or conducted, are or will affect
the governor systems operation, it is recommended to use shielded cable for all including the speed
sensor shield, is connected to a single point on the case of the speed control unit. Mount the speed
control unit to a grounded metal back plate or place it in a sealed metal box.
Conduction is when the interfering signal is conducted through the interconnecting wiring to the
governor system electronics. Shielded cables and installing filters are common remedies.
As an aid to help reduce the levels of EMI of a conductive nature, a battery line filter and shielded
cables are conveniently supplied by DWC.
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Instability
Instability in a closed loop speed control system can be categorized into two general types.
PERIODIC appears to be sinusoidal and at a regular rate. NON-PERIODIC is a random wandering
or an occasional deviation from a steady state band for no apparent reason.
Switch D1 controls the Differential function. When the position of switch D1 is "ON", the function is
operated. Move the switch to the "OFF" position if there is fast instability in the system.
The PERIODIC type can be further classified as fast or slow instability. Fast instability is a 3Hz. or
faster irregularity of the speed and is usually a jitter. Slow periodic instability is below 3Hz., can be
very slow, and is sometimes violent.
If fast instability occurs, this is typically the governor responding to engine firings. Raising the
engine speed increases the frequency of instability and vice versa. In this case, placing switch D1
in the "OFF" position will reduce the speed control unit's sensitivity to high frequency signals.
Should instability still be present, placing switch D2 to the "OFF" position may help stabilize the
engine. Again, readjust the GAIN and STABILITY for optimum control. Interference from powerful
electrical signals can also be the cause. Turn off the battery chargers or other electrical equipment
to see if the system disappears.
Slow instability can have many causes. Adjustment of the GAIN and STABILITY usually cures most
situations by matching the speed control unit dynamics. If slow instability is unaffected by this
procedure, evaluate the fuel system and engine performance. Check the fuel system linkage for
binding, high friction, or poor linkage. Be sure to check linkage during engine operation. Also look
at the engine fuel system. Irregularities with carburetion or fuel injection systems can change engine
power with a constant throttle setting. This can result in speed deviations beyond the control of the
governor system. Adding a small amount of droop can help stabilize the system for troubleshooting.
NON-PERIODIC instability should respond to the GAIN control. If increasing the gain reduces the
instability, then the problem is probably with the engine. Higher gain allows the governor to respond
faster and correct for disturbance. Look for engine mis-firings, an erratic fuel system, or load
changes on the engine generator set voltage regulator. If the throttle is slightly erratic, but
performance is fast, move switch D1 to the "OFF" position. This will tend to steady the system.
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