A PLC (i.e. Programmable Logic Controller) is a device that was invented to replace the necessary sequential relay circuits for machine control. The PLC works by looking at its inputs and depending upon their state, turning on/off its outputs. The user enters a program, usually via software, that gives the desired results.
PLCs are used in many "real world" applications. If there is industry present, chances are good that there is a plc present. If you are involved in machining, packaging, material handling, automated assembly or countless other industries you are probably already using them. If you are not, you are wasting money and time. Almost any application that needs some type of electrical control has a need for a plc.
For example, let's assume that when a switch turns on we want to turn a solenoid on for 5 seconds and then turn it off regardless of how long the switch is on for. We can do this with a simple external timer. But what if the process included 10 switches and solenoids? We would need 10 external timers. What if the process also needed to count how many times the switches individually turned on? We need a lot of external counters.
As you can see the bigger the process the more of a need we have for a PLC. We can simply program the PLC to count its inputs and turn the solenoids on for the specified time
Plc Control System Integration
PLC Control System Integration
The AutomationDirect.com DL405 series PLCs have two different types of base controllers: the Dl405 CPUs and the Ethernet Base Controller (EBC). The DL405 CPU’s provide traditional CPU/Ladder Logic type control of the PLC, whereas the EBC eliminates the CPU, and provides “pass thru” to allow the PC to control the PLC’s I/O directly.
In combination with the DL405 CPU, the Ethernet communications module allows the PC to read and write the PLC’s memory without special communication software in the PLC. This led to the idea of using a “dual port” memory model, where machine status and other parameters are communicated between the PLC and the control PC thru the PLC’s memory. This provides a system with PLC type control, but PC based remote configurability.
Channel information for CAMD’s control system is stored in a PostgreSQL database, and is organized by device type, with device specific parameters as needed. As the CAMAC channel information is organized by crate, slot, channel address, and channel type, this seemed logical approach to organize the PLC channel information. For the EBC type controller, this provided an exact match for the access method that the communications library provides.
For the CPU based controllers, additional abstraction is necessary. The DL405 CPU architecture provides a flexible memory map: inputs, outputs, control registers, and timers can be accessed directly, or as a “V memory” address.
