PMAC Product Guide WIRING GUIDELINES Proper wiring, grounding and shielding are essential to prevent unwanted electrical noise and to assure proper servo operation and performance. The most common symptoms resulting from improper wiring are inaccurate positioning, poor servo control and, in the worst case, will damage parts of the controller’s hardware. These are some known noise sources:
• Switches operating inductive loads such as relays and solenoids • Solid state relays or PWM servo amplifiers • Arc welding and plasma torch machines • Heavy current carrying wires • Fluorescent lights • Neon lights The following sections illustrate the most common wiring problems and methods for reducing electromagnetic noise. Ground Loops Ground is an equipotential circuit reference point. A ground loop can be defined as electrical grounds that are not at the same electrical potential, namely zero volts AC and DC. As a result, a ground loop generates a potential difference along the ground line connecting two electrical devices. This originates the following important consequences: 1.
An electrical current will circulate along the ground wire, dissipating power and generating heat. Wire insulators will be degraded and eventually damaged. 2. The ground electric potential will change resulting in a wrong signal reference. Some electrical signals in PMAC will change state above 0.7V against ground. If the ground reference rises above 1V an evident unreliable behavior will result. 3. In some cases the ground line is used as a safety mechanism against electric shocks. Therefore, the ground line must be kept as a zero volts reference point.
Star Ground Connection All component chassis ground points and signal ground or common points should be tied together at a single point (star connection). This point should then be tied with a single conductor to an earth ground point. This form of grounding prevents ground loops and ensures that all components are properly grounded against shock hazard. This configuration applies only for common ground connections and it does not apply for devices with opto-isolation circuits. If PMAC is powered with separate analog and digital power supplies (the recommended method) do not tie the PMAC analog and digital grounds together. Wiring Guidelines 23