Clear signals

Article#: 00079

Date: 2022-10-27

Author: Radim

A machine or a plant must run as autonomously as possible, and if an operator intervention is required, this must be clearly signaled to the operator in a timely manner.
When the operator approaches the machine, the condition of the machine must be clear to him at first sight (even from a distance). If the machine is not in optimal condition, it must guide the operator through the necessary steps.
When the operator wants to perform a function, the machine must clearly indicate to him which functions are currently performable, and for those that cannot be performed, it must be clear why they cannot be performed. After the operator has performed a function, it must be obvious to the operator whether the function has been successfully executed or not.
For these reasons, a clear and consistent signaling concept must be defined.
This means choosing appropriate signaling devices and their location, and clarifying signaling conventions (colors, styles, behavior).

The operator can be informed about the machine status from a distance of several meters within the production hall via an LED signal tower or a horn.
If a local part of the machine requires the operator's attention, it is possible to turn on a LED lamp only on that part of the machine.
A button that must or can be pressed by the operator should be illuminated. (e.g. safety reset button or machine start button etc.)

Some basic states can be easily signaled by light and sound signals. However, make sure that the signaling convention is not too complex (many LED colors, different flashing modes, different audible tones) and that the operator's work environment is not unnecessarily disturbed (e.g. loud and frequent honking for small things).
If there can be multiple reasons for a problem, it's a good idea to call the operator to the visualization panel, which clearly tells the operator where the problem occurred and how to fix it.
It is important to carefully consider which signals need to be activated in parallel. So that we don't get into a conceptual dead end when two states occur at the same time and we only have one signaling element available.

The colors of signal lights must be chosen carefully and with respect to international standards to eliminate the risk of misunderstandings and fatal errors.
In general, it's a good idea to avoid long-term activation of flashing lamps and horns, as these can be disturbing.
Since a flashing light attracts more attention than a steady light, the flashing signal can be a good way to call the operator closer to the problem area.
Select a suitable flashing period so that the flashing cannot be overlooked at first glance.
The horn must be able to be acknowledged/muted even if the cause is still active.

Properly designed signaling reduces machine downtime and increases productivity and safety. The right signaling can be described in the following words: clear, intuitive, simple, consistent, appropriate to the level of severity, correctly placed, functional.

© Radim-Automation, 2020–2025. All rights reserved.
Sharing of this article is permitted with proper attribution (link to the original page).

Related previous articles:

• Design considerations for effective HMIS
• Safety relays versus safety PLC
• Knowledge gained from a completed project is priceless
• Machine modularization
• Modular software architecture
• Hardware concept
• A good concept = Complete set of suitable solutions
• Think critically!
• Design machines with a focus on user's abilities and needs
• Learn from your journey!
• Collect all the requirements and sort them!
• Who will operate?
• Functional and intuitive HMI
• Use a usefull styleguide!
• HMI and PLC applications should grow together
• More than just start and stop
• Safety first!
• Don't make it worse!
• Industrial evolution - Listen to your customers and follow new trends!
• Stay alert!
• What does the customer need?
• Don't disappoint your customer!
• Ask questions!
• Focus on target!
• Check the result!
• Keep it simple!
• Don't leave a work package half-finished!
• Development is evolution
• Transparency and reliability
• From an idea to a consistent system

Related next articles:

• Talk to operators
• It doesn't work without sensors
• Event logger as the very first function implemented in the program
• Diagnostic tools
• PLC network diagram
• Keep the documentation up to date throughout the project
• Graphic designer
• High Performance HMI
• HMI - Have a consistent style
• HMI - Don't overdo it with complex design
• HMI is not a web page
• Choosing an HMI display
• HMI layout and correct display size
• HMI layout design
• HMI navigation
• HMI - back and forward navigation buttons
• HMI – Don’t hide anything
• HMI - colors in the visualization
• What makes an HMI intuitive?

Comment#: 00001

Date: 2022-10-28

User: Radim

"WHAT IS THE MEANING OF A RED BEACON LIGHT?
A red bacon light is usually associated with an emergency. This is also the case with red beacon lights on signaling devices. It stands for emergency, a dangerous or hazardous condition and requires immediate action. Signal lights with a red beacon light are suitable for signalling system failures, values that lie outside their safe limits (e.g. temperature) or if there is danger from moving or live goods. Immediate action that can be taken includes stopping or switching off motors or machines."
- https://www.auersignal.com/en/technical-information/visual-signalling-equipment/beacon-colors/

Comment#: 00002

Date: 2022-10-28

User: Radim

"WHAT IS THE MEANING OF A YELLOW AND AMBER BEACON LIGHTS?
Because of the high radiance of these colors, they are used to bring attention to something. Yellow and amber beacon lights indicate an imminent critical state and require human monitoring – or intervention. Signaling devices with a yellow or an amber beacon light are suitable for indicating overloads or exceeding of standard values if the duration is only permitted for a limited time. The required action steps serve the purpose of preventing the abnormal condition and avoiding resulting side effects. Precautions and warnings of moderate danger are suitable for the signal color yellow."
- https://www.auersignal.com/en/technical-information/visual-signalling-equipment/beacon-colors/

Comment#: 00003

Date: 2022-10-28

User: Radim

"WHAT IS THE MEANING OF AN ORANGE BEACON LIGHT?
Like the color yellow, the signal color orange indicates a warning. Orange stands for an imminent critical condition and requires monitoring or human intervention. Typical applications in which orange beacon lights are is the classic traffic light system in signal towers. The colors red-orange-green are often combined in three-stage signal towers. With these three signal colors, three different states of machines or similar applications can be displayed efficiently and quickly."
- https://www.auersignal.com/en/technical-information/visual-signalling-equipment/beacon-colors/

Comment#: 00004

Date: 2022-10-28

User: Radim

"WHAT IS THE MEANING OF A GREEN BEACON LIGHT?
The signal color green means a normal, perfect condition. No action is required. Typical applications with a green beacon light on a machine show that the machine is ready for operation or is running without malfunction. By lighting up, green signal lamps indicate normal operation of a machine or that a machine part or switchgear can be switched on.
The color green is to be understood as a safety color and should not be used for warnings or safety instructions. Safety instructions already indicate a possible danger and should therefore be signaled in blue."
- https://www.auersignal.com/en/technical-information/visual-signalling-equipment/beacon-colors/

Comment#: 00005

Date: 2022-10-28

User: Radim

"WHAT IS THE MEANING OF A BLUE BEACON LIGHT?
The signal color blue indicates a state that requires a defined action by the operator. Excluded are the states of the signal colors red, yellow, orange and green. Any other meaning can be assigned to the color blue."
- https://www.auersignal.com/en/technical-information/visual-signalling-equipment/beacon-colors/

Comment#: 00006

Date: 2022-10-28

User: Radim

"WHAT IS THE MEANING OF A CLEAR BEACON LIGHT?
The clear beacon light has no special meaning. In use, the clear dome is used for other conditions when there is doubt about the use of red, yellow, green or blue. Whether or not the illumination of the clear dome requires the supervision or intervention of an employee must be assessed individually for each application.
Under no circumstances should a clear dome be used for push buttons with stop or off functions. The radiance of clear beacon lights is very high, as it does not consume light transmission. Despite the high light transmission, a clear dome is not suitable for attracting attention to warn of danger."
- https://www.auersignal.com/en/technical-information/visual-signalling-equipment/beacon-colors/

Comment#: 00007

Date: 2022-10-28

User: Radim

"WHAT IS THE MEANING OF A MAGENTA BEACON LIGHT?
The color magenta, or often equated with purple, plays a major role, especially for applications in the USA. There, magenta beacon lights are used as an alternative to red beacon lights, if for example, the color red is assigned to fire hazard. Especially in the oil and gas industry, this signal color represents a particularly dangerous situation.
When a beacon light in the signal color magenta lights up, people should leave their surroundings immediately or actions should be carried out by trained personnel."
- https://www.auersignal.com/en/technical-information/visual-signalling-equipment/beacon-colors/

Comment#: 00008

Date: 2022-10-28

User: Radim

"In principle, the module with the highest alarm level is mounted at the top. The importance of the module decreases with descending order. This means that the topmost and most important modules are also particularly easy to recognise from a distance."
- https://www.auersignal.com/en/technical-information/visual-signalling-equipment/beacon-colors/

Comment#: 00009

Date: 2022-10-28

User: Radim

I used the red-orange-green signal tower in practice as follows:
RED FLASHING = machine has an alarm
RED STEADY = machine is stopped with no alarm
ORANGE FLASHING = machine has a warning
GREEN FLASHING = batch is complete (machine is awaiting next operator instruction)
GREEN STEADY = machine is running

For example, this combination: GREEN STEADY + ORANGE FLASHING = machine is running and has a warning.

Comment#: 00010

Date: 2022-10-28

User: Radim

The GREEN START BUTTON should be illuminated when the machine is stopped and ready to start. If there is no alarm on the machine.

Comment#: 00011

Date: 2022-10-28

User: Radim

The RED STOP BUTTON and GREEN START BUTTON should both be illuminated when the batch is complete and the user has the choice to stop the machine or start a new batch.

Comment#: 00012

Date: 2022-10-28

User: Radim

The BLUE SAFETY RESET BUTTON should be illuminated when the safety circuit is open, but with the safety reset button it is possible to close the safety circuit (when the emergency stop is no longer activated).

Comment#: 00013

Date: 2022-10-29

User: Radim

Usually we need a visualization screen near the start button of a machine or plant, because if the start is not allowed, the visualization tells us what restrictions are currently set and how to fix them.

Comment#: 00014

Date: 2022-10-29

User: Radim

When the machine is running, that means "EVERYTHING OK" in terms of production, but also "CAUTIOUS" in terms of safety.
The machine can also stand still temporarily, but it is just waiting for the activation of the next phase and it will start moving again.

Comment#: 00015

Date: 2022-11-06

User: Radim

"Give the operator visual and audible clues as affirmative feedback when buttons are pressed or when certain steps have been performed. This builds confidence and satisfaction with the system, and optimizes operator interaction."
- https://blog.isa.org/design-tips-effective-industrial-machine-process-automation-hmi
- Chip McDaniel. Design Tips to Create a More Effective HMI

Comment#: 00016

Date: 2023-07-14

User: Radim

"A good interface is easy to learn, leads to faster reaction time, safer operations and higher productivity. You deserve a system that is intuitive - one that at a glance you can see what actions need to be taken and is easy to navigate."
- General Electric (2021). Modern HMI/SCADA Guidebook for Efficient Operations.
- https://www.ge.com/digital/lp/modern-hmiscada-guidebook-efficient-operations

Comment#: 00017

Date: 2023-08-10

User: Radim

"The information that should be available on a graphical user interface (GUI) of a machine depends heavily on the type of machine and its application. However, here are some basic pieces of information that are often displayed on a GUI:

1. Status Information: The GUI should display important status information about the machine, such as whether it's powered on or operational, whether it has issues or error messages, and whether all systems are functioning properly.

2. Operational Parameters: Display the current operational parameters of the machine, such as speed, temperature, pressure, voltage, etc. This allows the user to monitor the machine's current state and make adjustments if needed.

3. Process Overview: If the machine is involved in an ongoing process (e.g., manufacturing, processing, analysis), relevant process data and steps should be displayed on the GUI. This helps the operator monitor the progress of the process and identify potential deviations.

4. Warnings and Error Messages: Display warnings or error messages if problems or critical situations arise. This enables the operator to react quickly and take appropriate actions.

5. User Interaction: Provide interfaces for user interaction, such as adjusting settings, changing parameters, or issuing commands. This includes buttons, dropdown menus, text fields, and other elements.

6. Historical Data: A history or log of past events and activities can be helpful for identifying trends, diagnosing errors, or making performance improvements.

7. Documentation and Help Material: Provide user manuals, help tutorials, or links to further information so that users can learn about operation, maintenance, and potential issue resolutions.

8. Visualizations: Depending on the application, charts, graphs, or visual representations of relevant data can be useful for recognizing relationships and trends more easily.

9. User Profiles and Settings: Allow users to create individual profiles and configure specific settings to match their workflow.

10. Safety Information: If the machine could potentially be hazardous, the GUI should display safety instructions, emergency stop buttons, or other safety mechanisms.

11. Contact Information and Support: Provide contact information for technical support or customer service in case users need assistance or support.

It's important to carefully design the GUI based on user needs and the type of machine to ensure a user-friendly and efficient experience."

- https://chat.openai.com (What information should be available in the machine's graphical user interface?)

Comment#: 00018

Date: 2024-07-03

User: Radim

Bear in mind that the operator sometimes operates the system in a panic and needs a short and fast route to the destination and a quick response from the system. The system must inform the operator of what has happened and what is expected of the operator.