Stack lights (also known as signal tower lights, indicator lights, andon lights, warning lights, industrial signal lights, or tower lights) are commonly used on equipment in industrial

manufacturing Manufacturing is the creation or production of goods with the help of equipment, labor, machines, tools, and chemical or biological processing or formulation. It is the essence of secondary sector of the economy. The term may refer to a ...

and

process control An industrial process control in continuous production processes is a discipline that uses industrial control systems to achieve a production level of consistency, economy and safety which could not be achieved purely by human manual control. ...

environments to provide visual and audible indicators of a machine's status to machine operators, technicians, production managers and factory personnel. They are a form of andon: a manufacturing system that identifies errors as they happen.

General

Stack lights are used in similar applications to beacon lights/strobes, however the information they typically display encompasses more machine/process conditions. Stack lights typically use

incandescent Incandescence is the emission of electromagnetic radiation (including visible light) from a hot body as a result of its high temperature. The term derives from the Latin verb ''incandescere,'' to glow white. A common use of incandescence is ...

LED A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (cor ...

or xenon-type strobes as their illumination source. Stack lights are generally columnar structures in a variety of shapes, placing colour-coded indicator segments on top of one another in a "stacked" orientation. A stack light will typically have up to five differently coloured segments to indicate various conditions on the machine or process. Segments in any combination of (typically) red, yellow, green, blue or clear white are actuated independently and are either off, steadily lit, or flashing. Stack lights are passive devices that may be controlled directly by programmable logic controllers,

distributed control system A distributed control system (DCS) is a computerised control system for a process or plant usually with many control loops, in which autonomous controllers are distributed throughout the system, but there is no central operator supervisory cont ...

s, PC control systems or hardwired to machine controls such as

timer A timer is a specialized type of clock used for measuring specific time intervals. Timers can be categorized into two main types. The word "timer" is usually reserved for devices that counts down from a specified time interval, while devices th ...

sensors A sensor is a device that produces an output signal for the purpose of sensing a physical phenomenon. In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends ...

and

latching relay A relay Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts An automotive-style miniature relay with the dust cover taken off A relay is an electrically operated switc ...

s. Discrete signals activate illuminated segments at common industrial control voltages (including 12Vdc, 24Vac/dc, 115Vac, 230Vac). Some units support

fieldbus Fieldbus is the name of a family of industrial computer networks used for real-time distributed control. Fieldbus profiles are standardized by the International Electrotechnical Commission (IEC) as IEC 61784/61158. A complex automated industrial ...

networked control through popular industrial networks such as

Modbus Modbus is a data communications protocol originally published by Modicon (now Schneider Electric) in 1979 for use with its programmable logic controllers (PLCs). Modbus has become a ''de facto'' standard communication protocol and is now a commo ...

DeviceNet DeviceNet is a network protocol used in the automation industry to interconnect control devices for data exchange. It utilizes the Common Industrial Protocol over a Controller Area Network media layer and defines an application layer to cover a ran ...

, Profibus, CAN-Open or ASi. Flashing control may be provided by the stack light's internal circuitry or externally controlled with timers or logic controllers. Stack lights are available for all types of industrial environments including washdown (

IP65 The IP code or ingress protection code indicates how well a device is protected against water and dust. It defined by the International Electrotechnical Commission (IEC) under the international standard IEC 60529 which classifies and pr ...

) and explosion proof.

Function

Stack lights are used in a variety of machines and process environments; specific colour-coding is assigned by the system designer. Commonly used colour codes for machine state conditions include: * RED: Failure conditions such as an

emergency stop A kill switch, also known as an emergency stop (E-stop), emergency off (EMO) and as an emergency power off (EPO), is a safety mechanism used to shut off machinery in an emergency, when it cannot be shut down in the usual manner. Unlike a normal ...

or machine fault * YELLOW: Warnings such as over-temperature or over-pressure conditions * GREEN: Normal machine or process operation * BLUE: External help request, where an operator might be requesting raw materials, scheduling or maintenance personnel assistance * WHITE: User-defined conditions to a specific machine, often related to productivity monitoring * Optionally an audible alarm

buzzer A buzzer or beeper is an audio signaling device, which may be mechanical, electromechanical, or piezoelectric (''piezo'' for short). Typical uses of buzzers and beepers include alarm devices, timers, train and confirmation of user input such as a ...

, typically in the range of 70–105dB, may be added to alert machine operators to high priority conditions. IEC60073 addresses machine state colour-coding & acoustic alerting, which can be applied to devices including panel pilot lights & stack lights. Machine operator intervention is typically required in red and yellow machine states, as these are normally errors or warnings. Manual intervention is possibly necessary in blue and white conditions.

Applications

Common applications include, but are not limited to: * Productivity monitoring (often rate-based machine output management with parts-per-hour displays). Uptime & downtime monitoring (

overall equipment effectiveness Overall Equipment Effectiveness (OEE) is a measure of how well a manufacturing operation is utilized (facilities, time and material) compared to its full potential, during the periods when it is scheduled to run. It identifies the percentage of ...

) is a very common use for these devices.
INTERNATIONAL JOURNAL OF SYSTEMS APPLICATIONS, ENGINEERING & DEVELOPMENT Issue 1, Volume 3, 2009. * Warning indication and machine fault management *

Lean manufacturing Lean manufacturing is a production method aimed primarily at reducing times within the production system as well as response times from suppliers and to customers. It is closely related to another concept called just-in-time manufacturing (J ...

- 5S Initiatives
Why a Visual Factory? , Visual Controls: Applying Visual Management to the Factory, by Ortiz & Park * In conjunction with SCADA, SCADA supervisory control systems and

user interface In the industrial design field of human–computer interaction, a user interface (UI) is the space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine f ...

/HMIs: SCADA/HMIs provide more specific machine/process status data; stack lights complement them by providing visual/audible feedback away from the machine operator console. * Assembly station

workcell A workcell is an arrangement of resources in a manufacturing environment to improve the quality, speed and cost of the process. Workcells are designed to improve these by improving process flow and eliminating waste. They are based on the principl ...

s * Maintenance call stations * CNC machining equipment and process monitoring and feedback * Broadcast studios (commonly used in broadcast radio studios) to display status of things such as a studio on air, live microphones, phone calls and even as a doorbell in an environment where silent indication is critical. * Dispatch centers where the dispatcher frequently uses a headset making it difficult to tell when the dispatcher is on the phone or radio. The light will light one color when the radio is keyed and another when on the phone.

References

{{reflist Control devices Types of lamp Industrial automation

General

Function

Applications

See also

References