PLC Programming: Ladder Logic Basics
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Questions and Answers

What is the standard value for the 'T R' in the Integer Files?

7

What range of files can be assigned by the user in the Integer Files?

9 - 255

What is the purpose of the 'OTL' instruction in the Basic Bit Instructions?

To latch a bit ON

What does 'XIC' stand for in the PLC Sequence Programming?

<p>Examine If Closed</p> Signup and view all the answers

What does ESET 225 refer to?

<p>PLC/Pneumatic Interfacing</p> Signup and view all the answers

What happens when the Output Energize (OTE) instruction is executed?

<p>It signals the PLC to energize or de-energize the output.</p> Signup and view all the answers

What is the function of the Output Latch (OTL) instruction?

<p>It can only turn on (Set) a bit.</p> Signup and view all the answers

What is the function of the Output Unlatch (OTU) instruction?

<p>It can only turn off (Reset) a bit.</p> Signup and view all the answers

How is the AND Logic used to control an output?

<p>Two switches in series are used.</p> Signup and view all the answers

How is the OR Logic used to control an output?

<p>Two switches in parallel are used.</p> Signup and view all the answers

What are the two logic solutions that can be designed to eliminate conflicts in control signals?

<p>One-shot [timed pulse] and Latching circuit</p> Signup and view all the answers

What is the advantage of using an additive sequencer to solve conflicts?

<p>The fastest way to solve conflicts is to design an additive sequencer, which is very similar to Relay Logic design.</p> Signup and view all the answers

What is the purpose of using memory bits in designing an additive sequencer?

<p>Memory bits are used for steps, and the steps are used to control output bits.</p> Signup and view all the answers

In the context of signal conversion circuitry, what should be checked before allowing motion to start?

<p>It is often advantageous to check that a machine is in the 'Rest' or 'Home' position before allowing motion to start, by ensuring that all rest position limits are ON.</p> Signup and view all the answers

What condition should be met for the 'Ready to start' in signal conversion circuitry?

<p>The 'RUN' bit should be on, the machine should be in the 'HOME' position, and the 'DONE' bit should not be on.</p> Signup and view all the answers

What is the symbolic set of instructions used to create the controller program?

<p>Ladder diagram language</p> Signup and view all the answers

What is the instruction that looks and operates like a normally open relay contact?

<p>Examine If Closed (XIC)</p> Signup and view all the answers

What should be used in a ladder program to determine if a bit is On?

<p>XIC instruction</p> Signup and view all the answers

What is the instruction that looks and operates like a normally closed relay contact?

<p>Examine If Open (XIO)</p> Signup and view all the answers

How is the XIO instruction evaluated when the bit addressed is off (0)?

<p>False</p> Signup and view all the answers

What are the two main types of symbols used in PLC programming?

<p>Contacts and Coils</p> Signup and view all the answers

How does a PLC determine if an input is on or off?

<p>By checking the input status</p> Signup and view all the answers

What is the main function of a PLC program?

<p>To control outputs based on the status of inputs</p> Signup and view all the answers

How is ladder logic similar to electrical ladder logic?

<p>It usually consists of two vertical 'rails' joined by horizontal logic 'rungs'</p> Signup and view all the answers

What is the main purpose of a computer monitor in PLC programming?

<p>To display more logic on the screen, simplifying interpretation of the program</p> Signup and view all the answers

What type of logic is used to control a warning horn with two limit switches?

<p>Series-parallel logic</p> Signup and view all the answers

How does a single acting cylinder convert energy into motion?

<p>Air pressure acts on one side of the piston and is returned by spring, gravity, or external force.</p> Signup and view all the answers

What helps strengthen and direct the magnetic field in a solenoid?

<p>An iron or steel C-frame</p> Signup and view all the answers

In what way can air pressure act in a double acting cylinder?

<p>Air pressure can act on both sides of the piston, and force is available in both directions.</p> Signup and view all the answers

How is the plunger of a solenoid connected to a valve spool?

<p>The plunger of a solenoid can be connected directly to a valve spool.</p> Signup and view all the answers

What is the purpose of the off-delay timer (TOF) operation in a PLC?

<p>To keep the output energized for a time period after the rung containing the timer has gone false.</p> Signup and view all the answers

When is a retentive timer (RTO) used in a PLC?

<p>When retaining accumulated time values through power loss or change in rung state from true to false is necessary.</p> Signup and view all the answers

What is the function of the reset (RES) instruction in a PLC?

<p>To reset a timer or counter with the same address as the RES instruction when enabled.</p> Signup and view all the answers

What is the purpose of the One Shot Rising (OSR) instruction in PLC programming?

<p>To turn on for one scan when the input goes from False to True.</p> Signup and view all the answers

Under what conditions does the ACC reset in a PLC?

<p>When rung g is true.</p> Signup and view all the answers

When does the DN set in a PLC?

<p>When .ACC ≥ .PRE.</p> Signup and view all the answers

What triggers the TT set in a PLC?

<p>When the rung is true and .ACC &lt; .PRE.</p> Signup and view all the answers

Under what conditions does the EN set in a PLC?

<p>When the rung is true.</p> Signup and view all the answers

When does the RTO reset in a PLC?

<p>When the rung is false or DN is reset.</p> Signup and view all the answers

What is the purpose of the TOF instruction in a PLC?

<p>To keep the output energized for a time period after the rung containing the timer has gone false.</p> Signup and view all the answers

Ladder Logic is used to program ______'s

<p>PLC</p> Signup and view all the answers

The Examine If Closed (XIC) instruction looks and operates like a normally open ______ contact

<p>relay</p> Signup and view all the answers

The Examine If Open (XIO) instruction looks and operates like a normally closed ______ contact

<p>relay</p> Signup and view all the answers

The ladder diagram language is a symbolic set of instructions used to create the controller ______

<p>program</p> Signup and view all the answers

Use the XIC instruction in your ladder program to determine if a bit is ______

<p>On</p> Signup and view all the answers

Use the XIO instruction in your ladder program to determine if a bit is ______

<p>Off</p> Signup and view all the answers

These files are organized by the type of data they contain. 10 Energy System Engineering 5 Addressing ______ File Type File Number Element Word Bit

<p>Tf:e.s/b</p> Signup and view all the answers

11 ______ Output & Input Files This files stores the statues of the Input / Output terminals of the controller.

<p>Tf:e.s/b</p> Signup and view all the answers

12 Energy System Engineering 6 ______ Output & Input Files T O for Outputs, I for inputs f not used all outputs are file 0, all inputs are file 1 :e Physical slot used (1 - max.available) slot 0 is reserved for CPU.s used to indicate word if > 16 bits in slot 0 - 15, not required if not more than 16 bits /b bit in word (0 - 15)

<p>Tf:e.s/b</p> Signup and view all the answers

13 I/O Address ______

<p>Format</p> Signup and view all the answers

14 Energy System Engineering 7 Status ______ The status data file contains information about the processor status This file stores controller operation information.

<p>File</p> Signup and view all the answers

In 1968 GM wrote the design criteria for a computer based “relay replacer.” This led to the development of the first ____________.

<p>PLC</p> Signup and view all the answers

As automated systems became more complex, relay control circuits became too large and unwieldy. Computer programming languages were not easy for factory electricians to use. This led to the need for a computer-based “relay replacer” known as the _________.

<p>PLC</p> Signup and view all the answers

Programmable logic controllers are now the most widely used industrial process control technology. A PLC is basically a digital computer designed for use in machine control. It has been designed to operate in the industrial environment and is equipped with special ________ interfaces and a control programming language.

<p>input/output</p> Signup and view all the answers

PLC’s Programmable logic controllers are now the most widely used industrial process control technology. A PLC is basically a digital computer designed for use in machine control. It has been designed to operate in the industrial environment and is equipped with special input/output interfaces and a control ________ language.

<p>programming</p> Signup and view all the answers

As automated systems became more complex, relay control circuits became too large and unwieldy. Computer programming languages were not easy for factory electricians to use. This led to the need for a computer-based “relay replacer” known as the _________.

<p>PLC</p> Signup and view all the answers

As automated systems became more complex, relay control circuits became too large and unwieldy. Computer programming languages were not easy for factory electricians to use. This led to the need for a computer-based “relay replacer” known as the _________.

<p>PLC</p> Signup and view all the answers

Step 2-EXECUTE PROGRAM-Next the PLC executes your program one instruction at a time.Maybe your program said that if the first input was on then it should turn on the first output.Since it already knows which inputs are on/off from the previous step it will be able to decide whether the first output should be turned on based on the state of the first input.It will store the execution results for use later during the next ______.

<p>step</p> Signup and view all the answers

Finally the PLC updates the status of the outputs.It updates the outputs based on which inputs were on during the first step and the results of executing your program during the second ______.

<p>step</p> Signup and view all the answers

One scan time is defined as the time it takes to execute the 3 steps listed ______.

<p>above</p> Signup and view all the answers

All the devices supplying information to the PLC are ______.

<p>Inputs</p> Signup and view all the answers

Any device to be controlled by the PLC must be connected to an ______ terminal.

<p>output</p> Signup and view all the answers

In 1968 GM wrote the design criteria for a computer based “relay replacer” which led to the development of the ________.

<p>PLC</p> Signup and view all the answers

A PLC is basically a digital computer designed for use in machine control. It has been designed to operate in the industrial environment and is equipped with special input/output interfaces and a control programming ________.

<p>language</p> Signup and view all the answers

Programmable logic controllers are now the most widely used industrial process control technology. A PLC is basically a digital computer designed for use in machine control. It has been designed to operate in the industrial environment and is equipped with special ________ interfaces and a control programming language.

<p>input/output</p> Signup and view all the answers

The ladder diagram language is a symbolic set of instructions used to create the controller ________.

<p>program</p> Signup and view all the answers

The Examine If Open (XIO) instruction looks and operates like a normally closed ________ contact.

<p>relay</p> Signup and view all the answers

The _________ is used to program PLC’s.

<p>Ladder Logic</p> Signup and view all the answers

The Examine If Closed (XIC) instruction looks and operates like a normally open ________ contact.

<p>relay</p> Signup and view all the answers

Use the XIC instruction in your ladder program to determine if a bit is ________.

<p>On</p> Signup and view all the answers

The Examine If Open (XIO) instruction looks and operates like a normally closed ________ contact.

<p>relay</p> Signup and view all the answers

PLC’s are equipped with special input/output interfaces and a control ________ language.

<p>logic</p> Signup and view all the answers

The structure of a PLC is based on the same principles as those employed in computer ______

<p>architecture</p> Signup and view all the answers

A personal computer (PC) is the most commonly used programming ______

<p>device</p> Signup and view all the answers

The CPU controls the entire ______

<p>PLC</p> Signup and view all the answers

The Examine If Open (XIO) instruction looks and operates like a normally closed ______ contact

<p>relay</p> Signup and view all the answers

The status data file contains information about the processor ______

<p>status</p> Signup and view all the answers

The main function of the program is to control outputs based on the status of ______.

<p>inputs</p> Signup and view all the answers

A PLC works by continually scanning a program. This scan cycle consists of 3 important steps. Typically the others are checking the system and updating the current internal counter and timer values. First, the PLC takes a look at each input to determine if it is on or off. In other words, is the sensor connected to the first input on? Step 1-CHECK INPUT STATUS-First the PLC takes a look at each input to determine if it is on or off. In other words, is the sensor connected to the first input ______?

<p>on</p> Signup and view all the answers

Contacts describe the information available to the control system. Coils cause the actions that the control system must perform. The interconnection of contacts and coils define the decisions that the system makes. The Examine If Closed (XIC) instruction looks and operates like a normally open ______ contact.

<p>relay</p> Signup and view all the answers

If all Input bits on a rung are “True”, then Output will be “ON.” Ladder Logic is used to program ______'s.

<p>PLC</p> Signup and view all the answers

The Examine If Open (XIO) instruction looks and operates like a normally closed ______ contact.

<p>relay</p> Signup and view all the answers

The Output Energize (OTE) instruction looks and operates like a ______ coil

<p>relay</p> Signup and view all the answers

OTL can only turn on (Set) a bit, while OTU can only turn off (Reset) a ______

<p>bit</p> Signup and view all the answers

The AND Logic uses two switches in ______ to control an output

<p>series</p> Signup and view all the answers

The OR Logic uses two switches in ______ to control an output

<p>parallel</p> Signup and view all the answers

OTL and OTU are retentive output instructions usually used in ______

<p>pairs</p> Signup and view all the answers

The Examine If Closed (XIC) instruction looks and operates like a normally open ______ contact

<p>relay</p> Signup and view all the answers

The Examine If Open (XIO) instruction looks and operates like a normally closed ______ contact

<p>relay</p> Signup and view all the answers

The status data file contains information about the processor ______

<p>status</p> Signup and view all the answers

Ladder Logic is used to program ______

<p>PLCs</p> Signup and view all the answers

The Output Unlatch (OTU) instruction is used to turn off (Reset) a ______

<p>bit</p> Signup and view all the answers

A conflict occurs when two opposing control signals are ON at the same time, i.e. A+ & A- Logic solutions can be designed to eliminate conflicts, using signal conversion circuitry: – One-shot [timed pulse] – ______ circuit

<p>Latching</p> Signup and view all the answers

The fastest way to solve conflicts is to design an ______ sequencer. Very similar to Relay Logic design. One rung for each step, and a Reset rung at end of sequence. Use memory bits for steps, and use steps to control output bits

<p>additive</p> Signup and view all the answers

It is often advantageous to check that a machine is in the “Rest” or “Home” position before allowing motion to start. Check that all rest position limits are ON. ______ for Home position to ensure safety

<p>Check</p> Signup and view all the answers

‘RUN’ bit for start. Ready to start condition (HOME). Not ‘DONE’ Latch bit on Use a memory bit for ______

<p>output</p> Signup and view all the answers

Actions are completed Latch current step Previous step is ON Use consecutive memory bits for ______

<p>steps</p> Signup and view all the answers

Study Notes

PLC Programming Basics

  • The standard value for the 'T R' in the Integer Files is not specified.
  • The user can assign a range of files in the Integer Files, but the specific range is not mentioned.
  • The 'OTL' instruction is used to latch an output, which means it can only turn on (set) a bit.

PLC Instructions

  • The 'XIC' instruction stands for Examine If Closed and looks and operates like a normally open relay contact.
  • The 'XIO' instruction stands for Examine If Open and looks and operates like a normally closed relay contact.
  • The 'OTE' instruction looks and operates like a normally open coil.
  • The 'OTL' instruction is used to latch an output, and 'OTU' instruction is used to unlatch an output.
  • The 'OTL' instruction can only turn on (set) a bit, while 'OTU' instruction can only turn off (reset) a bit.

Logic Control

  • The AND Logic is used to control an output by using two switches in series.
  • The OR Logic is used to control an output by using two switches in parallel.
  • Ladder Logic is used to program PLCs.

Conflict Resolution

  • A conflict occurs when two opposing control signals are ON at the same time.
  • Two logic solutions can be designed to eliminate conflicts: One-shot (timed pulse) and Retentive circuit.
  • The fastest way to solve conflicts is to design an Additive sequencer.

Signal Conversion Circuitry

  • Before allowing motion to start, it is often advantageous to check that a machine is in the “Rest” or “Home” position.
  • Check that all rest position limits are ON.
  • Ready to start condition (HOME) is not ‘DONE’ Latch bit on.

PLC Operation

  • A PLC works by continually scanning a program, which consists of three important steps: Check Input Status, Execute Program, and Update Output Status.
  • One scan time is defined as the time it takes to execute the three steps.
  • All devices supplying information to the PLC are inputs.
  • Any device to be controlled by the PLC must be connected to an output terminal.

PLC History

  • In 1968, GM wrote the design criteria for a computer-based “relay replacer,” which led to the development of the first PLC.
  • Programmable logic controllers are now the most widely used industrial process control technology.
  • A PLC is basically a digital computer designed for use in machine control, equipped with special input/output interfaces and a control programming language.

PLC Structure

  • The structure of a PLC is based on the same principles as those employed in computer design.
  • The CPU controls the entire PLC.
  • A personal computer (PC) is the most commonly used programming device.
  • The ladder diagram language is a symbolic set of instructions used to create the controller program.

PLC Files

  • The Integer Files are organized by the type of data they contain.
  • The Output File stores the status of the output terminals.
  • The Input File stores the status of the input terminals.
  • The Status File contains information about the processor status.
  • The Energy System Engineering File contains information about the controller operation.

Output Control

  • The Output Energize (OTE) instruction is used to turn on an output.
  • The Output Unlatch (OTU) instruction is used to turn off an output.
  • The Output Latch (OTL) instruction is used to latch an output.
  • The Output Unlatch (OTU) instruction is used to unlatch an output.

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Description

Learn the basics of programming a PLC using Ladder Logic, which is the main method for programming PLCs. Understand the use of symbols such as 'Contacts' and 'Coils' and how to control outputs based on input statuses.

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