PLC Flashcards

Flashcards about Programmable Logic Controllers (PLC)

What are the five PLC programming languages recognized by the International Electrotechnical Commission (IEC) Standard 61131-3?

Ladder diagram (LD), function block diagram (FBD), structured text (ST), sequential function chart (SFC), and instructional list.

What is the advantage of using a mixed language program in PLC programming?

It allows you to use the most suitable language for the application.

What type of PLC task executes all the time?

Continuous tasks

What type of PLC task is only executed when an event that triggers their execution occurs?

Event tasks

What is a routine in PLC programming?

The executable logic of a program in one of the programming languages.

What is a subroutine?

Any routine other than the main routine, and must be called from the main routine to be executed.

What is a fieldbus?

A digital network for communication with low-level industrial control and instrumentation devices. It links the control system to the sensors and actuators in the field and requires only one communication point to the control system, but allows multiple devices to connect to this point.

What are three common industrial fieldbuses?

DeviceNet, HART (highway addressable remote transducer), and Foundation Fieldbus.

What is a DeviceNet scanner?

A module that plugs into a PLC chassis and controls all the field communications on a DeviceNet segment, transmitting data to and receiving data from field devices.

What is a scan list in the context of DeviceNet?

A list of devices that communicate with the scanner, for which the scanner sets aside input or output memory for the data of the device.

What does the Highway Addressable Remote Transducer (HART) protocol do?

Superimposes a digital signal on a milli-amp current loop to provide two means of communication: an analog channel for the primary process variable and a digital channel for other process variables, status, diagnostics, and remote configuration.

What is a HART point-to-point topology?

A configuration where each HART instrument connects to its own unique connection point, with the main process variable transmitting along the analog channel and other information communicated digitally along a digital channel superimposed on the analog signal.

What does full HART integration allow for?

The configuration of HART devices and the collection of diagnostic information from an asset management system.

What is the function of a Foundation Fieldbus linking device (FFLD)?

Provides connectivity between field devices on an H1 network and the PLC controller.

What is redundancy in the context of PLCs?

A parallel or secondary system that takes over when the primary system fails so control can continue uninterrupted.

What are the three categories of availability?

Basic availability, high availability, and fault-tolerant.

What is a cross load in a high availability redundant PLC system?

Transfer of all the contents of a PLC's primary controller transfers to the secondary controller

What happens during a switchover?

The transfer of control from the primary controller to the secondary controller.

What is online editing?

The process of changing PLC programming while your process is running.

What is forcing in PLC programming?

Overriding a tags value. Forcing an input tag overrides the value from the input device. Forcing an output tag overrides your logic and sends the force value to the output device.

What is a Change Management System (CMS)?

Software package that resides on a workstation that connects to a controller-to-controller level network.