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PROCESS SAFETY
NEW GENERATION OF SIGNAL TOWERS ARE BRIGHTER AND SIMPLER TO ORDER AND MAINTAIN By Jacob Vernon, production manager, Pfannenberg
and alerts of dangerous conditions. They are relatively simple devices, but until recently, they have been notoriously difficult to configure, order and stock because of the proliferation of different sizes and options to meet the wide range of applications. Fortunately, a new generation of signal towers changes all this. New technology and new designs make state-of-the-art signal towers much brighter so that one size fits all applications and environments. Now, ordering signal towers is much easier and fewer spare parts are needed
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TYPICAL SIGNAL TOWER COLOUR SCHEMES Signal towers have been around for decades. They are also frequently called stack lights due to their vertical orientation. They contain up to five lights, of different colours, with each colour signifying a particular status, warning or alarm. Despite efforts to create international harmonised standards for indicator lights
ignal tower lights play a critical role in protecting the safety of people and equipment in manufacturing and process control environments, providing visual and audible indications of system status
and their meanings (e.g., IEC 60204-1, Fifth edition Chap. 10.3.2), implementations vary. In general, the following conventions are commonly applied:
RED is an alarm condition signifying an emergency or hazardous situation.
AMBER warns of an abnormal condition or an impending critical situation.
GREEN represents normal machine or process operation or a non-hazardous environment.
BLUE signifies an important/mandatory action that is not urgent, such as refilling a hopper with raw material or scheduling a service call.
WHITE does not have any universal designation. It is often used for productivity monitoring.
Within each colour category, the light can be continuous or it can blink intermittently to indicate a more urgent condition and to attract more attention.
Likewise, stack lights frequently incorporate a sounder module for audible signals for
A WIDE RANGE OF APPLICATIONS
Sometimes a stack tower will contain only two modules. For example, laser cutting machines may use a green light to indicate that the machine is on and everything is working properly, and a red light will flash when the laser is pointing downward in cutting mode to warn operators and to alert other workers to stay clear of the machine.
In addition to warning indication and machine fault management, signal towers are also commonly used for productivity monitoring (rate-based machine output management with displays counting parts per hour or parts per shift), as well as equipment effectiveness and productivity (uptime and downtime). In fact, stack towers are often called andon lights, for the andon system of quality control that is a principal component of the Toyota Production System. It empowers workers to stop production when a defect is found and immediately call for help.
In the andon system, a green light indicates that production is proceeding normally. Yellow signifies that a problem has appeared and the operator needs assistance, and red alerts supervisors that the problem needs further investigation.
14 JANUARY/FEBRUARY 2023 | INDUSTRIAL COMPLIANCE
more effective warning and alarming. Sounders can generate a variety of tones including simulated bells, continuous tones, and siren sounds.
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