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Kind of Noise Generated and What Kind of Noise Affects Operation of Servo System

FAQ No. FAQ02557

Primary Contents

Question

What kind of noise is generated when the Servo System is used? Also what kind of noise affects the operation of the Servo System?

Answer

1. What Is Noise?

Noise is an unexpected random signal. Some noise originates from natural phenomena, such as lightening, but most noise that actually affects the operation of a device is created artificially inside or external to the device. Think of noise as an artificially created signal that travels through a transmission path to another signal line.

2. Types of Noises

Noise Sources

Devices that cause rapid changes in voltage or current are noise sources.

The more rapid the changes, the higher the voltage, and the higher the current, the stronger the noise source becomes.

Coil surgeAn electrical surge is generated when the voltage applied to the coil is switched ON/OFF.Relay
Solenoid
Contactor
Capacitor charge currentWhen voltage is applied to the capacitor it causes a large charge current flow.Internal power source
Power source
Discharge device
Pulse voltagePulse voltage from PWM (See note.)Servo Driver
Inverter
Switching power
Arc dischargeRapid change in voltage when there is dischargeWelding machine
Discharge tube

Note:PWM (pulse width modulation) is a method used to alter the voltage. By switching the voltage ON/OFF at a fast switching frequency, the average voltage can be modified.

3. Transmission Path of Noise

There are the following four noise transmission paths.

(1) Electrostatic Coupling Line

Signals that change rapidly are transmitted through a capacitor between other signal lines that cannot be seen (an electrical field). The more rapid the signal change, and the closer the signal line, the easier it is to transmit the signal.

Effects

Noise transmission between signal cables

Leakage current of the motor

Malfunction of Sensors in mechanical system

(2) Conductive Coupling Line

Signals that change rapidly are transmitted through a conductor (such as cables and frame grounds (FG)) to signal lines and control devices.
Noise may be transmitted through the power lines, or pass through other noise transmission paths before being transmitted by conduction.

Effects

Malfunction of control devices

Noise from power system

(3) Electromagnetic Induction Line

Signals that change rapidly create magnetic fields that change rapidly in the surrounding. A magnetic field generates electromotive force in other signal lines. The more rapid the signal changes, and the closer the signal line, the larger the electromotive force.

Effects

Noise transmission between signal cables

Noise from the motor power lines

(4) Electromagnetic Wave Line

Signals that change rapidly create magnetic waves that are emitted using the signal lines as antennas. In a Servo System, noise may be come from the sections shown in the diagram on the right.

Effects

Noise from radio or television

Malfunction of Sensors that use electromagnetic waves