In every production plant there are many machines that require operation by an operator, i.e. a human. Sometimes the specificity of their operation requires the use of additional safety measures, as well as solutions enabling signaling of the operating status. This is particularly important when damage to an unattended machine may pose a threat to employees performing tasks on production lines. In order to reduce the risk of any incidents, acoustic or optical warning signals are commonly used. Most often, appropriate alarm signals are generated by signaling columns, which can be found primarily, but not only, on production lines. Such devices are often part of the basic equipment of new production machines.
How is a signal column constructed?
Depending on the selected configuration, the signal column can provide acoustic and/or optical warning signals. A piezoceramic transducer is most often used to generate the sound signal, while the light source is LED diodes. Together with their housing, they create light modules (light segments) enabling the generation of visual signals in various colors. There are various variants of signaling columns available on the market, which can be equipped with from 1 to even 7 light modules. Depending on your needs, the signaling column can be made modular or as a ready-made product (assembled in production according to the customer's specifications). The modular design allows for changing the arrangement/replacement/expansion of individual elements during the operation of the device. Signal columns are most often placed directly on or near machines so that the signals generated by warning devices are clearly visible even from greater distances. It is worth mentioning that signal columns may differ in the color of the casing, or mounting variant (straight or angular). It is very important that there are specific requirements for visual signals at the plant. Appropriate guidelines can be found, for example, in legal acts such as:
- Machinery Directive 2006/42/EC
- EN 981:1996+A1:2008 System of audible and visual distress signals and communication signals,
- Standard PN-EN 842+A1:2010 Safety of machinery - Visual danger signals - General requirements, design and testing
- Standard PN-EN 61310-1:2009 Safety of machinery - Indicating, marking and control - Part 1: Requirements for visual, acoustic and tactile signals
It is worth mentioning that the final requirements regarding visual signals may combine the information contained in the above legal acts with internal arrangements that cover the specificity of a given industrial plant.
Signaling column color meanings
As mentioned earlier, warning devices in the form of signaling columns are usually located on production lines (machines) or actuators of industrial automation. By default, the device is able to generate light in one, two or three colors. The general requirements include: green, which usually indicates the correct functioning of the machine, yellow (orange) indicates a warning or pause, and red indicates a state of danger or failure. Optionally, the signaling can be supplemented with blue, indicating the need to take mandatory action, or white, the meaning of which depends on the arrangements. It is worth mentioning that individual colors can be generated by continuous light, flashing light (with variable flash frequency), or stroboscopic light. Sometimes an irregular flash frequency or brightness modulation is also used, which further improves the visibility of the signaling. The above general requirements for visual signals are the most common. However, it should be borne in mind that individual arrangements on this matter may exist within a given plant.
What about the sound?
Due to the high noise levels on or near production lines, workers often have to wear hearing protection. This means that acoustic signaling alone may be insufficient or even ineffective. Additionally, controlling the signaling column allows you to control individual light modules (more than one module can be controlled at the same time), while only one acoustic alarm signal can be generated at a given time. In such a case, a signal of greater importance (assigned to the "more important" color) is usually generated. This is the so-called priority principle, according to which when several inputs are triggered at the same time, an acoustic signal assigned to the input with the highest priority is generated. For example, triggering the input responsible for green and yellow will trigger the acoustic signal assigned to yellow (higher priority). Similarly in the case of triggering the red and yellow colors, the acoustic signal assigned to the red color will be triggered as a signal of greater importance. When choosing signaling columns, it is worth paying attention to whether they are equipped with such an operating mechanism.
When it comes to patterns, a continuous signal with a constant frequency is most often assigned to the green color, a short single sound with a duration of over 0.3 s for the yellow color, and a series of short pulses for the red color, which is intended to immediately attract the attention of the operator or employee. In this way, it is possible to immediately determine whether a given signal requires the operator's attention. Determining the importance of acoustic safety signals helps significantly reduce response times, which helps improve and maintain production flow.
Which signal column to choose?
As you can see, there are many different solutions available on the market when it comes to signal columns. When choosing appropriate signaling columns, you should pay attention primarily to what light source they are equipped with (usually LED diodes), how many light modules (with what diameter) they have, and whether they have sound modules (the ability to generate acoustic alarm signals with a specific sound level), whether they have a priority mechanism, what type of construction they have (modular or "permanent"), as well as what color of the housing and mounting variant (straight, angular) is desired. Additionally, the signal column can provide optical warning signals in the form of continuous, flashing or irregular light. Also important is the control of the signaling column, which should enable connection of the device at the target location and possible integration with existing systems and installations. In particular, it is necessary to take into account what type of control signals a given column supports (e.g. triggering with a voltage of a specific value or the negative pole of the power supply, the so-called "ground"). This may be important for the design and proper installation of the entire installation. In addition, the signaling column can be equipped with RS232 or Ethernet communication ports, which facilitates work in complex systems where information exchange between devices is necessary. That is why the appropriate signaling column for a given application depends largely on the needs and expectations of the end customer.
