PMAC Product Guide Basic Rules for Proper Wiring 1. Take the time to sketch the system out before installing. This graphic representation of the installation will help avoid introducing ground loops and will serve as a road map for eliminating noise if it is present. 2. Do not introduce ground loops. Ground loops are created whenever a ground reference is established at more than one location. 3. Never run signal wires alongside power cables. This is true especially in installations where high- powered amplifiers are used. Large amplifiers are capable of drawing large currents. These currents vary the electromagnetic field surrounding the power cable.
The more current that flows through the wire, the bigger this field becomes. If signal cables are located in close proximity to this fluctuating electromagnetic field, noise could be induced into the system. Do not route signal and power wiring through common junctions. Consider using double-shielded cables if there is no way to separate the wires. 4. Use a shielded signal cable connecting only one end of the shield, preferably the source end (the point where the signal is generated). This will ensure maximum protection against induced noises by power cables and other sources of electromagnetic interference. 5.
Twist pairs of power wires from DC power supplies, DC brush motors and other high current cables. 6. Cable intersections should always occur at right angles to minimize magnetic coupling. 7. Keep signal cables short. PMAC’s JMACH cable should not exceed the 36 inches in length whereas PMACs JEXP cable should not exceed the 6 inches in length. 8. Use a separate analog and digital power supply. This will eliminate noise entering the digital circuits from the machine connections. 9. When possible use differential instead of single-ended signals. Differential signals will have common mode rejection for noise spikes.
If a single-ended signal is used, do not ground the remaining associated signal and leave it floating. The ACC-35A and ACC-35B pair is a good example of using differential signals for long distance connections. By using the ACC-35A and ACC-35B pair, PMAC’s JTHW connection can be extended from 3 to 100 meters for remote I/O operation. Noise spike will be suppressed by the common rejection mode of the differential input. 10. Use opto-isolation circuits when possible. Delta Tau provides a variety of opto-isolation boards for different signals. 11. A diode must be connected across a relay or solenoid coils in order to reduce inductive voltage. 12.
In some cases, when the electromagnetic noise affecting an input signal cannot be minimized otherwise, use an RC filter. The values of the RC filter must be selected carefully in order to not interfere with the safe operation of the input signal to filter. 26 Wiring Guidelines