Office: 127 Sanders Ferry Rd, Suite 300, Hendersonville, Tennessee , 37075, US

Phone: (615)-826-5559


George A. Shrokman, Jr. - The Industrial Door Geek

GS Control Systems LLC - Door Controls Engineering and Application



Terms used for industrial doors and controls.


Automatic Open Devices

Devices that open the door from the fully closed position when the control panel selector switch is in the "Auto" mode position. These devices also act the same as Reversing Devices once the door is off the floor and the fully closed limit contacts close.. Popular devices are Photo-eyes, loop detectors, motion sensors, presence sensors and laser detectors


Auto Mode

Controlled by the Hand / Auto Mode Selector Switch. Auto mode enables movement of the door by all devices connected to the system.


Auto Return to Dock

Used in Integrated Dock Systems. When the hydraulic dock leveler has the lip extended and bypasses the lip stored position, it will "bottom out" and then raise above the dock level and automatically lower itself down. When it goes back down the leveler lip is stored in what we call the "Home" position. At this time the Leveler Stored limit or proximity switch is held closed.


Bicycle Loop

A loop used with a loop detector that is specially designed for activation by bicycles, small hand carts, push carts, etc. We recommend signage and marking these areas with a painted surface.


Blue Light Area

A term used by the rail industry. Railroads basically use a Blue and Amber light for control. Vehicle traffic systems use a Red, Amber and Green signals for traffic control. A blue light basically means that humans are working in an area. A train cannot enter a blue light area. When there is an amber light, a train may enter an area. Blue and Amber lights are mounted above rail door openings to signal safe conditions. Blue light areas are determined by personnel from the Railroad Safety department. From our study of railroad regulations, there is no clear cut description of exactly when you are and are not required to have a Blue Light System. For safety purposes, we recommend all rail openings in buildings be designated Blue Light areas.


Cable Sensor

Sensor that monitors cable tension. When a cable comes loose or breaks the unit sends a signal to the control panel that shuts the system down.


Card Reader

A device that reads a card and enables a sequence. There are too many types of card readers to expand on them here. Literally any type of card reader can be adapted to the UAP.



A patented device that decodes a signal from a commercial radio and gives an output that the UAP processes. The unit can be interfaced with the UAP in certain ways. In most cases an Enabler signal is used to inform the UAP that the Click-2-Enter signal is to open or close a door. Open – Vehicle pulls up to the door and the Enabler senses the vehicle. The Click-2-Enter signal opens the door. When the vehicle has passed through the Auto Close Timer closes the door. Exit – Vehicle exits the door. Once the Enabler has detected a loss of vehicle on the inside of the building, the Click-2-Enter signal starts the door closed. If for some reason the door stops and reverses, the Auto Close Timer will automatically close the door.


Cross Traffic Loops

A loop layout used with loop detectors to prevent traffic coming across a door opening (not entering or exiting) from opening a door. See Loop Detectors

Delay Loop

A loop used with loop detector that do not send a signal to the control panel until a pre determined time delay has been reached. See Loop Detectors

Derail System

A unit used on railroads that purposely derails a train car moving towards a closed door. The rail door must be fully open before the derail is allowed to be removed from the tracks. The door cannot be closed while the derail is off track. This device is a base component of our Rail Safety Systems.


Diesel Sensor

A sensor that monitors the presence of diesel fumes in the air. When used with a Integrated Facility System (IFS) a pre determined amount of doors are usually opened 3 or 4 inches off the floor and remain there until the fumes are removed to a pre determined point. Then the doors close to the fully closed position automatically.


Dock System Integrated Panel

One control panel at a loading dock that combines the controls for (and not limited to) the door, dock leveler, truck restraint, air shelter, truck lift, etc.. This eliminates a separate control panel for each unit. All the units are interlocked to provide a safe and efficient operating system.



A device used to activate or make available a group of sensors or sequence. An example would be a 24 hour a day timer, used to change the sequence of operations at certain times of the day or night. Another would be an anemometer used to monitor the wind and automatically close a door when the wind is blowing hard.


Entrapment Photo Eye

Required by UL 325. Photo-eye is mounted just above floor level and is basically used to detect someone laying in the door opening. This unit is NOT used to detect vehicles, since vehicles are higher than the photo eye.


Four Door Vestibule

An entry or exit that consists of four operational units. Normally these consist of four doors with pairs mounted side to side to allow one way traffic through each pair.

Hand Mode

Controlled by the Hand / Auto Mode Selector Switch. Hand mode requires that a push button be physically pressed for the door to move.


Humidity Sensor

A sensor that monitors the humidity in an area and enables a change in the sequence of operations. A use for this is in a production facility where humidity effects the quality of materials in the area. An example would be in an steel coil facility, where high outside humidity would effect moisture in the steel coils and thus the quality of the steel. When humidity is low the doors would be allowed to remain open. When humidity is high, the doors automatically close after opening.


Laser Distance Beam

Laser device adapted to doors to detect presence in an area. Light beam is focused on an area, and when that distance is changed by an obstruction a set of contacts inside the unit change state. Unit can be wall mounted reading into an area or ceiling mounted and reading down to the floor.


Laser Photo Eye

A Photo Eye system that emits and receivers a laser beam. Units can be thru beam or retro reflective type. See Photo Eye


Laser Scanner (Rotary)

Wall mounted unit that scans an area approximately 150’ circumference (180 degrees) Unit is programmed by a computer to detect changes in definable areas within the sensing range. Because of the internal electronics, this unit can be considered a safety device. In applying this device you must remember that detection is by "line of sight" from wall mounted Laser Scanner. Note: Lasers used in these devices are classified as non harmless.

Leveler Stored Limit or Proximity Switch

Used in Integrated Dock Systems. This limit switch or proximity switch is mounted on the dock leveler and is activated by the dock leveler lip. The switch is wired normally open, and then held closed when the dock leveler lip is stored. This switch is used in the sequence of operations to interlock the dock leveler and truck restraint. If this limit switch is not held closed, the truck restraint will not release.


Loop Detector

A sensor that detects metallic objects and through microprocessor control sends notification of the change to a set of contacts in the control unit. The unit checks the change in the magnetic field by measuring a percentage change in Micro Henries in the loop area. The loops can be buried under ground, mounted on a side wall, or on the roof of a mine to detect mine vehicles. There are just too many applications to expand on the use of loops in this document.


Motion Detector

A device that detects movement within a pre-determined area. Units can use (but are not limited to) microwave or ultrasonic technology. Units vary in price and can be used to detect vehicles right at the door, or 300’ away. Doppler units can differentiate movement towards and away from the opening, as well as side to side movement. Always remember that MOVEMENT is required for motion sensors to work. If you want to detect stationary object, refer to Proximity Sensor


Motor Overhaul Detector

Sensor used to detect a change in the weight of the door. Control panel mounted unit shuts the system down when a pre-determined change occurs.


One Way Traffic

Vehicles only open the door when traveling in one direction.


Photo Eye

Light beam approximately ¼’" in diameter that is projected from a light emitter and detected by a light receiver. The emitted beam is detected by the receiver. A set of contacts inside the receiver indicate if a beam is present or not. A receiver that is wired for "Light Operate" energizes a set of contacts when the light beam is present. A receiver that is wired for "Dark Operate" energizes a set of contacts when the light beam is NOT present. We wire all of our units "Light Operate" and require the beam to be present for the system to operate properly.

Photo Eye Exterior

Exterior Door - A Photo Eye mounted in the exterior of the building no matter which side the door is mounted on.

Interior Door – A Photo Eye mounted on the opposite side of the door mounting side. Vestibule Doors - These devices are always on the outside of the vestibule.


Photo Eye Interior

A Photo Eye mounted in interior of the building

Exterior Door - A Photo Eye mounted in the interior of the building no matter which side the door is mounted on.

Interior Door – A Photo Eye mounted on the same side as the door mounting side. Vestibule Doors - These devices are always on the inside of the vestibule.


Radio Control

Any unit consisting of a transmitter and a receiver that activates a door. Most individuals relate this to your home garage door. Residential transmitters can be used with commercial and industrial doors. We recommend units designed for industrial and commercial use, such as Click-2-Enter and Enrange. These units are designed for rugged use and end up costing less on a yearly life expectancy basis.


Rail Door Integrated System

A system that not only protects a door, but also warns personnel inside a building that a train is moving inside the building .A system consisting of an integrated door control system, a derail unit, a light unit above the rail door, and rotating beacons and bells inside the building along the rail tracks.

Restraint Interlock

Used in integrated dock systems. The vehicle restraint must have the vehicle restrained in a safe condition before the integrated devices are allowed to operate.


Retro Reflective Photo Eyes.

Photo-eye having the emitter and receiver in the same unit. We do not consider retro-reflective photo eyes to be safe, and do not authorize their use with any of our systems. Retro Reflective units emit a modulated light beam across the door opening. The modulated light beam is reflected back to the unit by a special reflector. A set of contacts inside the unit indicate the light condition. Also See Photo Eyes.


Reversing Devices

Devices that stop and / or reverse the door (depending on the sequence of operations) when the door is closing. This device also resets the Auto Close Timer when the door is in the fully open position. These devices have no effect on the door when it is fully closed. Popular devices are Photo-eyes, loop detectors, motion sensors, presence sensors and laser detectors


Reversing Edge

Device mounted to the leading edge of a door used to detect an object blocking the movement of the door. We do not call this a "Safety Edge" since the device is NOT actually manufactured in a way that it contains the redundancy in the unit to consider it a Safety device. Reversing edges come in many different forms, and end up electrically operating in 2 wire, 3 wire or 4 wire configurations. We only consider 4 wire as being "Fail Safe". The basic unit is wired for 4 wire configuration, but by properly installing jumper wires, a 2 wire and 3 wire system can be used.


Sequence of Operations

A description of exactly how an action in the control system creates a reaction. A normal sequence of operations gives a general description of how a system works. A detailed sequence of operation references the electrical drawing numbers with each device operation and reaction.


Spring Break Sensor

Sensor that monitors a torsion spring. When a torsion spring breaks the unit sends a signal to the control panel that shuts the system down.


Thru Beam Photo Eyes

Photo-Eye consisting of an emitter (sometimes called a transmitter) and receiver. A modulated light beam is sent by the emitter and received by the receiver. A set of contacts inside the receiver indicate the light condition. Also See Photo Eyes.


Two Door Vestibule

An entry or exit that consists of two operational units (2 doors, 1 gate & 1 door, etc.).


Two Way Traffic

Vehicles can open the door from both sides of the opening.


Ultrasonic Sensors

Unit using sound waves to detect changes within an area. We normally do not use these devices since many industrial facilities have sound frequencies in the area that effect their operation. They work fine in commercial non production areas.


Vehicle Approaching Signal

Signals when a vehicle is entering an area. Normally used when openings are close to side walks or streets. An example would be a parking garage door or fire station door that is right on or near a sidewalk. When a vehicle is coming through or approaching the door, a horn and/or light on the outside of the building signals pedestrians or traffic.


Vestibule System

An entry or exit that has two or more doors used to control security or air passage into an area. Sequences in vestibules can vary from application to application. We have a complete list of standard recommended sequences available based on over 30 years of application experience.


Wheel Sensor (Rail)

Proximity sensor that bolts to a rail and detects a wheel on a rail car or crane.

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