2. Make sure the ground is connected to all devices.These are typically color coded as green, or have a ground symbol. Note: power should not flow through the ground, it is only for emergencies to draw current out of the cases of electrical equipment, and into the ground beneath the building. In other words the ground and common are not the same thing.
3. Normally the AC has 2 wires (for a single phase). For consumer applications we need to make sure the polarity is correct, so that the ‘hot’ (black) wire is switched off, making electrical shocks less likely. Note: in reality, even if these wires are backwards the power will still be delivered to the load.
5. Try not to daisy chain power connections (like a string of christmas lights), but connect the power cord to a terminal strip (power bus), and then connect to each device to the terminal strip. (see the figure)
6. Do not leave loose, or exposed wires. These will only lead to short circuits, electric shocks, or other problems. Tighten the wires. If doing this for permanent jobs, the wire should also wrap around the screw. Note: leads with banana plugs or ALIGATOR CLIPS ARE PARTICULARLY PRONE TO CREATING SHORT CIRCUITS.
2. The ground and common are terms that are badly confused/misused. A true ground is an electrical connection to the ground beneath a building that will draw away current if there is an electrical fault. A common is a reference voltage for all parts of a circuit, typically 0V. When connecting devices such as sensors and actuators we want to connect them to a common. This problem is normally overlooked, but when we have systems with mixed power sources (eg. 115Vac, low voltage DC) we must separate these. Do not connect the common to the ground. BE WARNED, many low voltage devices (such as power supplies, sensors, etc.) show the common as a ground.
Pre-Lab (Done individually)(NOTE: These, and all other Pre-labs will be checked before every lab. A mark of zero will be assigned when prelab materials have not been completed before the start of the laboratory):
3. Write a simple ladder logic program for a task of your own (individual) choosing. Describe the task briefly in words, and then develop a Boolean equation. Other techniques, such as truth tables may be useful. The program should use some/all of the inputs and outputs described in step 1.