Electrical
Amps - Volts - Ohms!

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More electrical/electronic technical drawing and circuit diagram examples, with short explanations, are being compiled to feature on this page. The purpose of them is to give a pictorial referance as an electrical technical drawing with an explanation of what's going on within it.

This helps in getting used to seeing different types of technical drawing (for those that aren't used to them).
For those that are more technically minded, there are some more advanced technical drawings and techniques being drawn up as well as some basic stuff. Perhaps they may even give you a new idea or two? Stayed tuned!

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Typical PLC wiring set-up with a 24V DC supply.

This little electrical circuit shows a typical wiring set-up for a DC supplied PLC, the S/S terminal is a sink or source connection.

The sink or source terminal allows for different types of input sensors to be connected. In this example, the proximity sensor connected to PLC input X7 is a 'PNP' type, it refers to the internal switching transistor type.

This type of sensor supplies 24V DC to the PLC input terminal on being energised. As such the sink/source must be connected to 0V or common to provide a circuit. Of course for the switches, such as the start and reset buttons it's not important whichever way they're connected, but for sensors, in this case a PNP type.

The proximity sensor would not work with the sink/source connected to the +24V DC and the supply side of the switches to the 0V DC, although the buttons would work fine either way.

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Tapping off existing signals for the PLC.

This is an example of how electrical signals can be tapped off from an existing control circuit. The operation signal from top terminal of a control relay (on the right) is fed off through a diode to prevent any back feeding of false signal to the machine control. This relays terminal is a positive 24V DC when the relay is energised and so supplies the PLC input with the same.

The diode is not essential but it is in place as a good practice measure. When a machine is being fault found, engineers introduce signal voltage at various points in the process of investigating a fault. The diode provides separation from the machine and from being joined to another PLC terminal on the machine that may cause a 'lock up' situation, or even damage.

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More examples are being compiled to be added in this section, as this page builds it will provide a useful reference.

See the Definition of Machine/Management Information Systems.

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