Baldor ID15J101-ER, Installation And Operating Manual

Page: 68 / 89

MN715J Troubleshooting 5-9
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 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, 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 ever-present 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 5-4 illustrates noise suppression for AC and DC operated coils.
Figure 5-4 Diode with DC Coil
AC Coil
DC Coil
RC snubber
0.47 m f
Diode
-
+
33 W
Wires between Controls and Motors
Output leads from a typical 460 VAC drive controller contain rapid voltage
rises created by power semiconductors switching 650V in less than a
microsecond, 1,000 to 10,000 times a second. These noise signals can
couple into sensitive drive circuits. If shielded pair cable is used, the coupling
is reduced by nearly 90% compared to unshielded cable.
Even input AC power lines contain noise and can induce noise in adjacent
wires. In some cases, line reactors may be required.
To prevent induced transient noise in signal wires, all motor leads and AC
power lines should be contained in rigid metal conduit, or flexible conduit. Do
not place line conductors and load conductors in same conduit. Use one
conduit for 3 phase input wires and another conduit for the motor leads. The
conduits should be grounded to form a shield to contain the electrical noise
within the conduit path. Signal wires - even ones in shielded cable should
never be placed in the conduit with motor power wires.