Back to Basics: Limit switches for conveyors

Process monitoring and control improves with proper application of limit switches in conveyor applications. See diagram.


An industrial conveyor belt usually consists of two or more pulleys, with a continuous loop of material (belt) that rotates around them. One or both pulleys are powered, moving the belt and the material on the belt forward. There are two main industrial classes of belt conveyors: general material handling (moving boxes along inside a factory) and bulk material handling (transporting industrial/agricultural materials).

Limit switches are used to provide conveyor system monitoring and control as well as safety in case of a problem. A limit switch is a precision snap-action switch that has been encased to protect it from external forces, such as hazardous chemicals, water, oil and dirt, and is used to detect presence or absence in areas where physical contact is allowed.

Discrete sensors, properly applied, can improve usefulness and lower risk of a conveyor application. Courtesy: Honeywell Sensing & Control

In the conveyor belt application shown, a variety of limit switches can be used.

1. Often used on conveyors designed for use in harsh indoor and outdoor environments, heavy-duty limit switches can reliably indicate position for system controls. In this configuration, the limit switch could be used to count the items flowing through it. It could also be used to ensure that materials are correctly positioned and will sound an alarm or stop the belt if there is a problem.

2. Safety switches: Cable-pull limit switches are emergency stop switches that control access around the conveyor perimeter or provide emergency-stop cable-pulls along the conveyor. These kinds of limit switches provide a highly reliable, highly visible, safe-to-use rope-pull device to protect operators working near conveying systems.

3. Hazardous location switches are very similar to switch 1 but are housed in sealed enclosures to prevent a spark or electrical discharge from setting off an explosion. They are often used for door or diverter position detection in outdoor, above-ground, potentially explosive environments, such as grain handling and oil and gas applications.

4. Safety and hazardous location switches have also been designed with an explosion-proof housing. Often used in outdoor, above-ground, potentially explosive environments, such as grain handling conveyors, or oil and gas applications, hazardous location switches can quickly and reliably stop system operation when the switch is triggered by the operator.

Limit switches can also be used in other ways on conveyor belts. For example, a limit switch alongside the belt could ensure that packages and materials are correctly positioned on the conveyor belt. The limit switch signal connects to a controller that will stop the belt if there is a problem.

To prevent jamming the belt’s discharge, limit switches could measure the number or height of the products on the conveyor belt. If too much product is going down the belt, the system will shut down before damage or spillage occurs.

- Richard Staiert is Honeywell applications engineer. Edited by Mark Hoske, CFE Media, Control Engineering, 

Honeywell Sensing & Control – Micro Switch limit switches information 

Sensors Channel 

Control Engineering tutorials 

No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
Safety for 18 years, warehouse maintenance tips, Ethernet and the IIoT, GAMS 2016 recap
2016 Engineering Leaders Under 40; Future vision: Where is manufacturing headed?; Electrical distribution, redefined
Strategic outsourcing delivers efficiency; Sleeve bearing clearance; Causes of water hammer; Improve air quality; Maintenance safety; GAMS preview
SCADA at the junction, Managing risk through maintenance, Moving at the speed of data
Safety at every angle, Big Data's impact on operations, bridging the skills gap
The digital oilfield: Utilizing Big Data can yield big savings; Virtualization a real solution; Tracking SIS performance
Applying network redundancy; Overcoming loop tuning challenges; PID control and networks
Driving motor efficiency; Preventing arc flash in mission critical facilities; Integrating alternative power and existing electrical systems
Package boilers; Natural gas infrared heating; Thermal treasure; Standby generation; Natural gas supports green efforts

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
This article collection contains several articles on the vital role of plant safety and offers advice on best practices.
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.
This article collection contains several articles on strategic maintenance and understanding all the parts of your plant.
click me