PLC: PLC1 PMMI Study Guide Exam
with Actual Detailed Answers 2026-
2027 Latest Update.
Describe the function of a programmable logic controller and give an application - Answer
PLCs are industrial computers that control machines and other industrial applications. PLCs have
replaced hardwired devices, such as relay coils and contacts
PLC applications - Answer Assembly machines
Automatic Transfer Lines
Packaging LInes
Robots
List the advantages of a PLC - Answer Less space
Lower Cost
Resistance to Environment
Direct Interface
Easy Programming
Flexible
Advantages - Direct Interface - Answer Standard computers require a complex and limited
system to interface to real-world components. A PLC's interface is directly wired to these
components
6 Components of a PLC - Answer Input Modules
Output Modules
Processor Module (or Controller)
PLC Power Supply
Programming Device
I/O Chassis
Describe the Basic Operation of a PLC - Answer To scan instructions, monitor the status of
input devices, and produce outputs based on the status of the inputs.
Describe how I/O modules communicate with the PLC processor - Answer Each input, or field
device, opens and closes circuits to an individual terminal on an input module. When an input
or output module is configured, each terminal is assigned a tag that identifies the location of
, the terminal status. The input module transmits (multicasts) the data to the system on a regular
basis so that the processor can collect the information via scan and enact logic/programming
based on input/output data/signal
Basic PLC Processor Operation - Answer Controller contains a ladder logic program that
references the tags of the input devices and similar tags of output devices. The controller then
uses that input information to determine the status of each individual rung of its program. The
status of the rungs are then transferred to an output tag where the output module turns the
real world devices on and off appropriately
Basic Operation of Serial Communication - Answer USB connects a host, which initiates a
data transaction with a device. USB groups the binary data from the host into fields, which are
then organized into packets. Packets are bundled into frames, which are transmitted to the
device over a half-duplex differential pair of wires (D+ and D-). Ones and zeros are determined
by voltage difference between D+ and D-. A 1 is defined as D+ 200 mV greater than D- and 0 is
defined as D+ 200 mV less than D-
Recognize Languages used to program a PLC - Answer Ladder Logic
Sequential Function Chart
Structured Text
Function Block Diagram
Sequential Function Chart - Answer uses a flowchart-like language that uses steps and
transitions to control a process or application. SFC programming is an effective method of
programming an application that uses a fixed sequence of inputs and outputs
Structured Text - Answer High level Programming language that uses text statements to
define the operation of the PLC. Structured text programming is often used in PLC applications
that involve a lot of math or data conversion
Function Block Diagram - Answer Graphical programming language that encapsulates other
programming languages (e.g. instruction list, structured text, etc.) into blocks. The blocks are
then assembled and connected together so that it appears similar to an electronic circuit. FBD is
most useful in applications involving a high degree of information/data flow between control
components, such as process control
Ladder Logic - Answer Resembles a ladder with rungs. Looks and operates very similar to the
hardwired relay systems.
Identify the function and purpose of a tag - Answer Tags are text-based names given to PLC
memory locations. They are used to store information about conditions both internal and
external to the PLC
with Actual Detailed Answers 2026-
2027 Latest Update.
Describe the function of a programmable logic controller and give an application - Answer
PLCs are industrial computers that control machines and other industrial applications. PLCs have
replaced hardwired devices, such as relay coils and contacts
PLC applications - Answer Assembly machines
Automatic Transfer Lines
Packaging LInes
Robots
List the advantages of a PLC - Answer Less space
Lower Cost
Resistance to Environment
Direct Interface
Easy Programming
Flexible
Advantages - Direct Interface - Answer Standard computers require a complex and limited
system to interface to real-world components. A PLC's interface is directly wired to these
components
6 Components of a PLC - Answer Input Modules
Output Modules
Processor Module (or Controller)
PLC Power Supply
Programming Device
I/O Chassis
Describe the Basic Operation of a PLC - Answer To scan instructions, monitor the status of
input devices, and produce outputs based on the status of the inputs.
Describe how I/O modules communicate with the PLC processor - Answer Each input, or field
device, opens and closes circuits to an individual terminal on an input module. When an input
or output module is configured, each terminal is assigned a tag that identifies the location of
, the terminal status. The input module transmits (multicasts) the data to the system on a regular
basis so that the processor can collect the information via scan and enact logic/programming
based on input/output data/signal
Basic PLC Processor Operation - Answer Controller contains a ladder logic program that
references the tags of the input devices and similar tags of output devices. The controller then
uses that input information to determine the status of each individual rung of its program. The
status of the rungs are then transferred to an output tag where the output module turns the
real world devices on and off appropriately
Basic Operation of Serial Communication - Answer USB connects a host, which initiates a
data transaction with a device. USB groups the binary data from the host into fields, which are
then organized into packets. Packets are bundled into frames, which are transmitted to the
device over a half-duplex differential pair of wires (D+ and D-). Ones and zeros are determined
by voltage difference between D+ and D-. A 1 is defined as D+ 200 mV greater than D- and 0 is
defined as D+ 200 mV less than D-
Recognize Languages used to program a PLC - Answer Ladder Logic
Sequential Function Chart
Structured Text
Function Block Diagram
Sequential Function Chart - Answer uses a flowchart-like language that uses steps and
transitions to control a process or application. SFC programming is an effective method of
programming an application that uses a fixed sequence of inputs and outputs
Structured Text - Answer High level Programming language that uses text statements to
define the operation of the PLC. Structured text programming is often used in PLC applications
that involve a lot of math or data conversion
Function Block Diagram - Answer Graphical programming language that encapsulates other
programming languages (e.g. instruction list, structured text, etc.) into blocks. The blocks are
then assembled and connected together so that it appears similar to an electronic circuit. FBD is
most useful in applications involving a high degree of information/data flow between control
components, such as process control
Ladder Logic - Answer Resembles a ladder with rungs. Looks and operates very similar to the
hardwired relay systems.
Identify the function and purpose of a tag - Answer Tags are text-based names given to PLC
memory locations. They are used to store information about conditions both internal and
external to the PLC
