How do I choose the right signal tower for my machine or production line?
What does a signal tower do, and why is the right selection important?
Signal towers (also known as stack lights or tower lights) are used to provide a clear, immediate indication of a machine or system status.
Typical status indications include:
- Operation / machine running
- Fault / error
- Hazard / stop
- Maintenance required / intervention needed
- Full bin / empty packaging
- Start or stop signal
A well-selected signal tower improves:
- Safety (faster detection of hazards or faults)
- Efficiency (reduced downtime through clear status feedback)
- Process reliability (better communication between operators and maintenance)
Factors that determine which signal tower you need
1. Determine the environment in which the signal tower will be installed
Pay attention to the following aspects:
- Noise level: In loud environments (80–100 dB), an acoustic signal alone may be insufficient without an amplified sounder or high-dB alarm.
- Light conditions: In brightly lit production halls or outdoor areas, high-intensity LED or Xenon strobe lights perform better.
- Environmental factors: Consider dust (IP65/IP67), moisture, temperature or chemical vapours.
- Production halls: often large viewing distances and high ambient light levels.
- Process installations: potential explosion risks may require ATEX-certified signalling devices.
- Warehouses: high traffic → 360° visibility is essential.
2. Choose the appropriate number of segments and colours
Common colour codes (EN ISO 13850 & EN ISO 7731):
- Red – emergency stop / hazard / fault
- Yellow – warning / intervention
- Green – normal operation
- Blue – action request / operator assistance
- White – process active / custom indication
3. Choose between LED, Xenon or rotating light technologies
LED signals
- Long service life
- Energy-efficient
- High visibility
- Ideal for indoor applications
- Extremely high light intensity
- Suitable for brightly lit production areas
- Commonly used for critical or high-priority alarms
- High contrast with a clearly moving visual pattern
- Well suited for environments with a lot of visual noise
4. Is an acoustic signal required?
Pay attention to:
- Sound level (dB): the alarm must be clearly louder than the background noise.
- Frequency (pitch): certain tones stand out better in specific environments.
- Signal pattern: for example continuous, pulsed or rising, depending on the application.
5. Consider mounting and connection options
When selecting a signal tower, it is also important to consider the available mounting and connection options. The way the tower is installed and wired determines whether it fits properly into your system and can be maintained easily. Pay attention to the following points:
Mounting options: choose a suitable installation method for your machine or production line, such as base mounting, pole mounting or wall mounting.
Supply voltage: check which voltages are supported, for example 24V DC, 48V DC or 115/230V AC.
Communication: determine the required control method, such as digital I/O, AS-i or IO-Link (increasingly used in modern automation).
Cable entry: consider the type of connection, such as M20, M12, connectors or fixed cables.
Modular systems, such as the signal towers from Pfannenberg, offer a high degree of flexibility. They allow different modules to be combined and easily adapted to your specific application.
6. Which standards apply to industrial optical and acoustic signalling?
When selecting a signal tower, it is important to consider the standards and guidelines that apply to industrial signalling. These define how a visual or acoustic signal must be designed to ensure safety, recognisability and clarity. The most relevant standards and directives include:
- EN ISO 13850 – guidelines for emergency stop principles and safe stop functions.
- EN ISO 7731 – requirements for acoustic warning signals, including sound levels and signal patterns.
- EN 981 / EN ISO 7010 – definitions of visual signals, colours and symbols used in industrial environments.
- Machinery Directive 2006/42/EC – general safety requirements for machinery, including signalling requirements.
- ATEX 2014/34/EU – requirements for signalling devices used in potentially explosive atmospheres.
A signal tower must always be clearly noticeable, recognisable and unambiguous according to these standards. This ensures correct interpretation of safety warnings and helps reduce risks in the workplace.
Practical tips for selecting the right signal tower
- Position the signal tower high enough to ensure an unobstructed line of sight.
- Use sufficiently high light intensity in daylight conditions or over long viewing distances.
- Combine visual and acoustic signalling in noisy environments.
- Use a maximum of five segments to keep status interpretation clear.
- Consider IO-Link for modern automation and advanced diagnostic functions.
Selecting the right signal tower depends on the environment, light conditions, noise level, number of status indications, light technology and applicable standards.
By considering visibility, audibility, modular design and compliance with standards, you can choose a system that improves safety, reduces downtime and enhances communication between personnel.
Brands such as Pfannenberg offer robust industrial signal towers with high light output and reliable acoustic modules, suitable for a wide range of industries.
