Baldor MN850 用户手册
5-4 Troubleshooting
MN850
Electrical Noise Considerations
All electronic devices are vulnerable to significant electronic interference signals
(commonly called “Electrical Noise”). At the lowest level, noise can cause intermittent
operating errors or faults. From a circuit standpoint, 5 or 10 millivolts of noise may cause
detrimental operation. For example, analog speed and torque inputs are often scaled at 5
to 10VDC maximum with a typical resolution of one part in 1,000. Thus, noise of only 5
mV represents a substantial error.
(commonly called “Electrical Noise”). At the lowest level, noise can cause intermittent
operating errors or faults. From a circuit standpoint, 5 or 10 millivolts of noise may cause
detrimental operation. For example, analog speed and torque inputs are often scaled at 5
to 10VDC maximum with a typical resolution of one part in 1,000. Thus, noise of only 5
mV represents a substantial error.
At the extreme level, significant noise can cause damage to the drive. Therefore, it is
advisable to prevent noise generation and to follow wiring practices that prevent noise
generated by other devices from reaching sensitive circuits. In a control, such circuits
include inputs for speed, torque, control logic, and speed and position feedback, plus
outputs to some indicators and computers.
advisable to prevent noise generation and to follow wiring practices that prevent noise
generated by other devices from reaching sensitive circuits. In a control, such circuits
include inputs for speed, torque, control logic, and speed and position feedback, plus
outputs to some indicators and computers.
Relay and Contactor Coils
Among the most common sources of noise are the coils of contactors and relays. When
these highly inductive coil circuits are opened, transient conditions often generate spikes
of several hundred volts in the control circuit. These spikes can induce several volts of
noise in an adjacent wire that runs parallel to a control-circuit wire. Figure 5-1 illustrates
noise suppression for AC and DC relay coils.
these highly inductive coil circuits are opened, transient conditions often generate spikes
of several hundred volts in the control circuit. These spikes can induce several volts of
noise in an adjacent wire that runs parallel to a control-circuit wire. Figure 5-1 illustrates
noise suppression for AC and DC relay coils.
Figure 5-1 AC and DC Coil Noise Suppression
AC Coil
DC Coil
RC snubber
0.47
m
f
Diode
-
+
33
W
Control Enclosures
Motor controls mounted in a grounded enclosure should also be connected to earth
ground with a separate conductor to ensure best ground connection. Often grounding
the control to the grounded metallic enclosure is not sufficient. Usually painted surfaces
and seals prevent solid metallic contact between the control and the panel enclosure.
Likewise, conduit should never be used as a ground conductor for motor power wires or
signal conductors.
ground with a separate conductor to ensure best ground connection. Often grounding
the control to the grounded metallic enclosure is not sufficient. Usually painted surfaces
and seals prevent solid metallic contact between the control and the panel enclosure.
Likewise, conduit should never be used as a ground conductor for motor power wires or
signal conductors.
Special Motor Considerations
Motor frames must also be grounded. As with control enclosures, motors must be
grounded directly to the control and plant ground with as short a ground wire as possible.
Capacitive coupling within the motor windings produces transient voltages between the
motor frame and ground. The severity of these voltages increases with the length of the
ground wire. Installations with the motor and control mounted on a common frame, and
with heavy ground wires less than 10 ft. long, rarely have a problem caused by these
motor–generated transient voltages.
grounded directly to the control and plant ground with as short a ground wire as possible.
Capacitive coupling within the motor windings produces transient voltages between the
motor frame and ground. The severity of these voltages increases with the length of the
ground wire. Installations with the motor and control mounted on a common frame, and
with heavy ground wires less than 10 ft. long, rarely have a problem caused by these
motor–generated transient voltages.
Analog Signals
Analog signals generally originate from speed and torque controls, plus DC tachometers
and process controllers. Reliability is often improved by the following noise reduction
techniques:
and process controllers. Reliability is often improved by the following noise reduction
techniques:
•
Use twisted-pair shielded wires with the shield grounded at the drive end only.
•
Route analog signal wires away from power or control wires (all other wiring types).
•
Cross power and control wires at right angles (90
°
) to minimize inductive noise
coupling.