Omron Symbols Glossary: Complete Guide to Omron Symbols, Meanings & Uses

An Omron symbols glossary helps users understand the icons, abbreviations, labels, and symbols commonly found on Omron products, manuals, control systems, and technical documentation.

 Because Omron manufactures equipment across automation, sensing, control, safety, healthcare, and other categories, the meaning of a symbol depends on the specific product and documentation.

This guide explains common Omron symbols and their meanings, how to interpret symbols on Omron industrial equipment, what common electrical and PLC-related abbreviations mean, and how to find the correct symbol information for a particular Omron product.

What Is an Omron Symbols Glossary?

An Omron symbols glossary is a reference for understanding symbols and technical markings associated with Omron equipment.

These symbols may appear on:

• PLCs
• HMIs
• Sensors
• Relays
• Timers
• Counters
• Safety devices
• Temperature controllers
• Industrial switches
• Power supplies
• Control components
• Medical and healthcare products
• Product labels
• Wiring diagrams
• Instruction manuals
• Software interfaces

Not every Omron symbol has a universal meaning across every product family. A symbol on an Omron PLC may represent an electrical or programming function, while a symbol on an Omron blood pressure monitor may communicate a health-related status.

For that reason, the safest approach is to interpret a symbol together with its product family, model number, manual, and applicable standard.

Why Understanding Omron Symbols Matters

Correctly interpreting technical symbols can help users install, operate, troubleshoot, and maintain equipment safely.

Faster Troubleshooting

Recognizing an indicator symbol can help identify whether a device is operating normally or reporting an error.

Easier Wiring

Electrical symbols and terminal markings help technicians understand how components should be connected.

Better PLC Programming

PLC symbols, addresses, instructions, and status indicators help programmers understand control logic.

Safer Equipment Operation

Warning and safety symbols can communicate hazards or required precautions before a user operates equipment.

Easier Manual Reading

A glossary can make technical documentation easier to understand, especially when several abbreviations appear on the same page.

Omron Symbols Glossary at a Glance

The following table provides a practical starting point. Exact meanings can vary by Omron product and manual.

These are general technical abbreviations rather than a single official Omron-wide symbol dictionary.

Common Omron Status Symbols and Indicators

Many Omron industrial devices use LEDs or display indicators to communicate operating status.

PWR or Power Indicator

A PWR or power indicator generally shows that electrical power is being supplied to the device.

Depending on the product, the indicator may have different states or colors.

Always consult the model-specific manual before assuming that a particular LED color means a specific condition.

RUN Indicator

A RUN indicator commonly relates to normal operation or execution.

On a PLC or controller, it may indicate that the control program or system is running.

ERR or Error Indicator

An ERR or error indicator generally signals an abnormal condition.

Possible causes depend on the device and can include:

• Hardware problems
• Configuration errors
• Communication problems
• Programming errors
• Power-related issues
• Sensor or I/O faults

The indicator alone does not identify the exact cause. The product’s troubleshooting documentation should be checked.

ALM or Alarm Indicator

An ALM indicator commonly represents an alarm condition.

The exact alarm can vary significantly between product families.

Omron Electrical Symbols and Abbreviations

Omron control components use many standard electrical abbreviations.

Understanding these terms is useful when reading wiring diagrams.

NO — Normally Open

NO means normally open.

A normally open contact does not conduct in its normal, unactivated state. When the associated device operates, the contact can close.

NO contacts are common in:

• Push buttons
• Relays
• Limit switches
• Control circuits

NC — Normally Closed

NC means normally closed.

A normally closed contact conducts in its normal state and opens when actuated.

NC contacts are commonly used in:

• Stop circuits
• Safety circuits
• Limit switches
• Relays

COM — Common

COM usually means common terminal or common connection.

Its exact electrical function depends on the component.

A COM terminal may be associated with:

• Relay contacts
• Input circuits
• Output circuits
• Switching circuits

Never assume that all COM terminals have the same electrical potential.

DC — Direct Current

DC means direct current.

It is commonly used in control systems and industrial electronics.

Typical control voltages can include 24 V DC, but the correct voltage must always be taken from the product’s specifications.

AC — Alternating Current

AC means alternating current.

It is used in many power and control applications.

The allowable voltage and frequency depend on the specific Omron device.

PE — Protective Earth

PE generally identifies a protective-earth connection.

It is an important electrical safety connection and should be wired according to the equipment documentation and applicable electrical regulations.

FG — Frame Ground or Functional Ground

FG can refer to a frame or functional ground connection depending on the product.

Its exact purpose must be confirmed using the relevant wiring diagram because grounding terminology can differ between devices.

Omron PLC Symbols and Terms

Omron offers programmable logic controllers and related automation equipment. PLC documentation contains its own terminology and symbols.

PLC

PLC stands for Programmable Logic Controller.

A PLC receives inputs, executes a control program, and controls outputs.

A simplified system can be represented as:

Inputs → PLC → Program Logic → Outputs

I/O

I/O means Input/Output.

Inputs allow a controller to receive information from devices such as:

• Push buttons
• Sensors
• Switches
• Encoders

Outputs can control:

• Relays
• Motors
• Solenoid valves
• Lamps
• Other control devices

Input Symbols

An input represents information received by the PLC or control system.

Examples include:

• Start button
• Stop button
• Proximity sensor
• Photoelectric sensor
• Limit switch

Output Symbols

An output represents a signal produced by the controller.

Examples include:

• Motor command
• Solenoid activation
• Indicator lamp
• Relay output

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Omron PLC Address Symbols

PLC programming often uses addresses to identify inputs, outputs, memory areas, and other data.

The exact address notation depends on the Omron PLC family and programming environment.

For example, Omron systems can use different memory-area conventions depending on the controller.

Common concepts include:

• Input areas
• Output areas
• Work areas
• Holding areas
• Timer areas
• Counter areas
• Data memory

Because address assignments are model- and software-dependent, users should consult the programming manual for the specific PLC rather than applying a generic address table to every Omron controller.

Omron Timer and Counter Symbols

Timers and counters are common concepts in PLC programming.

Timer

A timer allows a control program to respond based on elapsed time.

A simplified example is:

Input ON → Timer starts → Preset time reached → Output activates

Counter

A counter tracks events or pulses.

For example:

Sensor detects product → Counter increases → Preset count reached → Output activates

Timer and counter instructions can vary between Omron PLC generations and programming platforms, so the exact instruction name and symbol should be verified in the appropriate Omron documentation.

Omron Sensor Symbols

Omron manufactures many types of industrial sensors.

Common sensor categories include:

• Photoelectric sensors
• Proximity sensors
• Fiber-optic sensors
• Vision sensors
• Measurement sensors
• Safety sensors
• Encoders

Photoelectric Sensor

A photoelectric sensor detects objects using light.

A simplified concept is:

Emitter → Light beam → Object → Receiver

The actual sensor symbol used in a schematic depends on the diagramming convention.

Proximity Sensor

A proximity sensor detects an object without requiring physical contact.

Inductive proximity sensors are commonly used to detect metal objects.

Safety Sensor

Safety sensors are designed for machine safeguarding applications.

Examples include safety light curtains and other protective sensing systems.

Because safety equipment is involved, the symbol, wiring, and operating requirements should always be interpreted using the exact product documentation.

Omron Relay Symbols

Relays use electrical symbols to show their coils and contacts.

A basic relay may contain:

• Coil
• Normally open contact
• Normally closed contact
• Common connection

The relay coil controls the state of its associated contacts.

Relay Coil

The coil represents the electromagnetic component that operates the relay.

Relay Contacts

Relay contacts can be:

• Normally open
• Normally closed
• Changeover contacts

The exact schematic symbol depends on the relay configuration and the applicable drawing standard.

Omron Switch Symbols

Omron manufactures many types of switches and control devices.

Common examples include:

• Push buttons
• Selector switches
• Limit switches
• Rotary switches
• Rocker switches
• DIP switches
• Tactile switches

Push Button Symbols

A push button may be represented as either normally open or normally closed depending on its contact arrangement.

Limit Switch Symbols

Limit switches detect mechanical movement or position.

They can be used to determine whether:

• A door is closed
• A machine has reached a position
• A mechanism has reached its travel limit

The physical appearance and schematic symbol should not be confused. The product itself may look different from the electrical symbol used in a circuit diagram.

Omron HMI Symbols

An HMI, or Human-Machine Interface, allows operators to interact with an industrial control system.

HMI screens can contain symbols representing:

• Motors
• Valves
• Pumps
• Sensors
• Alarms
• Production status
• Temperature
• Pressure
• Flow
• Machine states

These graphical elements are often configured by the system designer rather than representing a single universal Omron symbol.

Alarm Symbols

Alarm icons generally communicate that a monitored condition requires attention.

Status Symbols

Status graphics can indicate conditions such as:

• Running
• Stopped
• Ready
• Faulted
• Manual mode
• Automatic mode

The exact meaning should be defined by the HMI application and its documentation.

Omron Safety Symbols

Safety symbols deserve particular attention because they may indicate hazards, mandatory actions, or important precautions.

Common safety concepts include:

• Warning
• Caution
• Electrical hazard
• Protective earth
• Read the manual
• Emergency stop
• Safety-related functions

Warning Symbols

A warning generally indicates a condition that could result in injury or damage if instructions are ignored.

Caution Symbols

A caution generally draws attention to conditions requiring careful handling or operation.

The exact meanings and severity classifications should be taken from the product’s official documentation rather than inferred from the icon alone.

Omron Medical Device Symbols

Omron also produces healthcare products, including home blood pressure monitors and other medical devices.

These products can use symbols that differ from industrial automation terminology.

Examples may relate to:

• Battery status
• Cuff positioning
• Measurement status
• Memory
• Irregular heartbeat detection
• User profiles
• Date and time
• Bluetooth or connectivity

Because these symbols can relate to health measurements, the specific product manual should always take priority over a general symbol glossary.

Omron Blood Pressure Monitor Symbols

Blood pressure monitors can display several indicators during or after a measurement.

Depending on the model, users may encounter symbols associated with:

• Blood pressure readings
• Pulse
• Cuff placement
• Irregular heartbeat
• Body movement
• Memory
• Battery
• Connection status

Why Model-Specific Information Matters

Different Omron blood pressure monitors do not necessarily use exactly the same display icons.

Therefore, if you are trying to identify a symbol on an Omron healthcare product, use the model number to locate the correct instruction manual.

A general glossary should be treated as a starting point, not a substitute for the product-specific manual.

Omron Symbol Colors and LED Indicators

Users sometimes search specifically for the meaning of Omron red, green, orange, or other indicator lights.

The important point is that LED color does not have one universal meaning across every Omron product.

For example, an indicator color may represent:

• Normal operation
• Warning
• Error
• Communication
• Power
• Sensor detection
• A specific machine state

The same color can have different meanings on different product families.

Therefore:

Do not diagnose a device solely from LED color.

Check the model-specific manual and indicator table.

How to Read an Omron Wiring Diagram

Reading an Omron wiring diagram becomes easier when you understand the basic sequence.

Step 1: Identify the Product

Find the exact model number.

Step 2: Identify the Power Supply

Determine whether the device uses:

• AC
• DC
• A particular voltage range

Step 3: Find the Terminals

Look for labels such as:

• Power
• COM
• Input
• Output
• Ground
• Communication

Step 4: Identify Input and Output Connections

Determine which terminals receive signals and which terminals provide signals.

Step 5: Check Contact Types

Identify whether contacts are:

• NO
• NC
• Changeover

Step 6: Check the Wiring Diagram

Compare the physical terminals with the official schematic.

Never rely solely on a generic diagram if the device is connected to live electrical equipment.

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Omron Symbols vs. Standard Electrical Symbols

An important distinction is that many symbols appearing in Omron documentation are not proprietary symbols.

They may be based on established electrical, electronic, automation, or engineering conventions.

For example:

• NO = normally open
• NC = normally closed
• AC = alternating current
• DC = direct current
• PE = protective earth

These are widely used technical conventions.

Other symbols may be specific to:

• An Omron product
• A particular PLC family
• An Omron software environment
• A particular HMI application
• A particular medical device

This is why a model number is often essential when identifying an unfamiliar symbol.

Common Mistakes When Interpreting Omron Symbols

Assuming Every Omron Symbol Is Universal

Omron has many product categories, so symbols can vary considerably.

Ignoring the Model Number

The model number is often the fastest way to find the correct manual.

Treating an LED Color as Universal

An orange or red indicator does not necessarily mean the same thing on every device.

Confusing Physical Icons With Schematic Symbols

The icon printed on a product may not be the same as the electrical symbol used in a circuit diagram.

Guessing Terminal Functions

Never assume that similarly named terminals have identical functions across different products.

Using an Old Manual for a New Model

Product revisions can change specifications, terminal layouts, and indicator meanings.

Ignoring Safety Instructions

Electrical and industrial equipment should be installed and serviced according to the manufacturer’s instructions and applicable regulations.

How to Find the Meaning of an Unknown Omron Symbol

If you encounter a symbol you do not recognize, use a systematic approach.

1. Find the Model Number

Look for the complete product or series number on the device.

2. Identify the Product Category

Determine whether it is:

• PLC
• Sensor
• Relay
• Switch
• Controller
• HMI
• Safety device
• Healthcare product

3. Locate the Official Manual

Use Omron’s official documentation for the exact model.

4. Search the Manual for the Symbol

Look at sections such as:

• Indicator meanings
• Terminal descriptions
• Wiring
• Specifications
• Error messages
• Display symbols
• Safety precautions

5. Compare the Symbol With the Diagram

Make sure the symbol is being interpreted in the correct context.

Omron Symbols Glossary: Quick Reference

Frequently Asked Questions About Omron Symbols

What does the RUN symbol mean on an Omron PLC?

RUN generally indicates that the PLC or control system is in a running or operating state. The exact indicator behavior depends on the specific PLC model.

What does ERR mean on an Omron device?

ERR generally indicates an error or abnormal condition. The exact cause must be determined from the device’s indicator table, error code, or troubleshooting documentation.

What does ALM mean on an Omron controller?

ALM generally means alarm and indicates that an alarm condition has occurred. The specific condition depends on the controller and its configuration.

What does PWR mean on an Omron device?

PWR usually means power and indicates the status of the device’s power supply.

What do NO and NC mean on an Omron relay?

NO means normally open, while NC means normally closed. They describe the contact state when the relay is in its normal, non-energized condition.

What does COM mean on an Omron relay?

COM generally means the common terminal associated with a contact set. Its exact electrical relationship should be confirmed from the relay’s wiring diagram.

What does I/O mean in Omron automation?

I/O means input/output. Inputs receive signals from field devices, while outputs send control signals to other devices.

What does PLC mean in Omron documentation?

PLC means Programmable Logic Controller, a type of industrial controller used to monitor inputs, execute programmed logic, and control outputs.

Why do Omron symbols differ between products?

Omron manufactures products across several industries and product categories. Some symbols follow standard electrical conventions, while others are specific to a particular product, software environment, or application.

How can I identify an unknown Omron symbol?

Find the exact model number, identify the product category, and consult the official instruction manual or technical documentation for that model.

Are Omron symbols standardized?

Some Omron symbols and abbreviations are based on widely recognized electrical and engineering conventions. Others are product-specific. Therefore, not every symbol should be assumed to have a universal meaning across all Omron equipment.

Conclusion

An Omron symbols glossary is useful for understanding the technical language found on Omron equipment and documentation, but there is no single symbol dictionary that applies identically to every Omron product.

Common terms such as PWR, RUN, ERR, ALM, COM, NO, NC, AC, DC, PLC, I/O, HMI, PE, and FG provide a useful foundation for reading industrial and electrical documentation.

At the same time, specialized symbols can differ between PLCs, sensors, relays, controllers, HMIs, safety products, and healthcare devices. The same indicator color or abbreviation may therefore have a different meaning depending on the product.

For the most accurate interpretation, identify the exact Omron model number and use its official documentation. This is particularly important for wiring, electrical connections, safety equipment, and medical devices.

A good glossary should help you understand the terminology, but the manufacturer’s model-specific manual should remain the final reference whenever a symbol affects installation, operation, troubleshooting, or safety.
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I can also create an image showing the most common Omron symbols, abbreviations, and their meanings as a visual glossary.

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Ryan Mitchell

I’m Ryan Mitchell, and I write about modern English, trending slang, and online expressions. I enjoy explaining the meanings, origins, and real-life usage of popular words in a simple way. I believe learning slang is an important step toward understanding today’s English-speaking culture. Through my work, I aim to help readers speak more naturally and stay updated with the latest language trends.