Stack light

General

Stack Lights (aka Indicator Lights, AndOn Lights, Warning Lights, Tower Lights & Light Towers) are commonly used on equipment in industrial manufacturing and process control environments. Stack Lights provide immediate Visual & Audible Feedback about a machine state or process event to Machine Operators, Technicians, Production Managers, and other factory personnel. Stack Lights are used similarly to Beacon Lights/Strobes, however, they typically encompass more machine/process conditions. Stack Lights typically use incandescent, LED or Xenon-type Strobes as their illumination source.

Stack Lights come in a variety of shapes, though as a general rule, they are columnar structures placing colored indicator segments on top of one another in a "stacked" orientation. A Stack Light will typically have up to 5 colored segments in any combination of Red, Yellow, Green, Blue, Clear/White that are used to indicate various conditions on the machine/process. Colored Segments are either:

• OFF
• ON (Solid On/Continuous)
• FLASHING

Stack Lights are passive control devices that are either hardwired to machine controls such as timers, sensors, latching relays, etc. or, more commonly, controlled directly by PLC's (Programmable Logic Controllers), DCS's (Distributed Control Systems) or PC Control Systems. Discrete signals activate illuminated segments at common industrial control voltages (12Vdc, 24Vac/dc, 115Vac, 230Vac). Some units support Fieldbus Connectivity allowing networked control with popular industrial networks such as Modbus, DeviceNet, Profibus, CAN-Open, ASi and others. Flashing control may be integral with internal circuitry to the Stack Light or externally controlled with Timers/Logic Controllers.

Examples

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Function

Since Stack Lights are used in such a variety of machines and process environments, there are no fixed rules about what a specific color represents to a machines state . The following color code could be loosely applied in most applications:

• RED Colored Segments = Failure Conditions such as an E-Stop Trip or Machine Fault
• YELLOW Colored Segments = Warning Conditions such as Over-Temperature or High Head Pressure
• GREEN Colored Segments = Normal Machine/Process Operating Conditions
• BLUE Colored Segments = External Help Request, where an operator might be requesting Raw Materials or assistance from Scheduling or Maintenance Personnel
• WHITE Colored Segments = User Defined Conditions specific to a machine, often related to productivity monitoring
• Optionally, an Audible Alarm (Buzzer) may be added to alert machine operators and others using audible stimulus. This is typically in the range of 70-105db and reserved for high priority conditions.

Application

Common Applications include, but are not limited to, the following:

• Productivity Monitoring (often rate based machine output management, sometimes with parts-per-hour displays). Up-time & Down-time monitoring is a very common use for these devices.
• Warning Indication/Machine Fault Management
• Lean Manufacturing - 5S Initiatives
• In conjunction with SCADA Supervisory Control Systems and User Interface/HMI's. These devices provide more specific machine/process status data & Stack Lights are compliment them by providing visual/audible feedback away from the machine operator console.

Manufacturers

• Onyx Industries
• Edwards Signal
• Idec
• Rockwell Automation
• Patlite
• Werma
• Eaton

References

• Engineering/Installation Reference Guide, http://www.onyx-industries.com/downloads/StackLightEngineeringReferenceGuide.pdf
• Lean Manufacturing "AndOn", http://www.superfactory.com/topics/andon.html
• Lean Manufacturing Glossary, http://www.gembutsu.com/articles/leanmanufacturingglossary.html