Self Opening Gates – How Do They Work?
Have you ever wondered how self opening gates actually work?
Automatic gates open and close when you press the button on a remote transmitter. Others can be operated from the house when a visitor calls from an intercom installed at the gate.
But self opening gates seem to open and close by themselves just as the homeowners drive towards them on their way out.
These self opening gates use special devices and controls to achieve egress (exit) control and this article explains how this happens.
How Do ‘Regular’ Automatic Gates Open And Close?
Automatic gates need motors to make them move. They have built in control systems to tell the motors what to do and how to behave differently when they receive information from the system’s additional components. These can include safety devices to help prevent contact with moving gates.
You will also be able to instruct your automatic gates to open and close. This could be via radio signals sent when you push a button on a hand-held remote transmitter. Or, you could have access control intercoms that allow you to communicate with visitors at your driveway gates so you can decide whether to let them in or not.
How Do Automatic Gates Avoid Hitting Things?
Automatic gate systems must be designed to be as safe as possible. To avoid hitting anything as they move, they need sensors to detect cars, pets and people. Some of these safety sensors are built into the gate’s motors while others are installed on or near the gates.
If the gates encounter resistance as they move, the ‘obstacle detection’ built into some gate motors stops the gates and makes them back off to allow whatever was in the way to move to safety.
Obviously, obstacle detection in this form requires contact with the moving gates. Safety edges play a similar role. These are like rubber tubes that are mounted onto walls and the gates.
If the safety edge on a moving gate comes into contact with something or someone, the rubber is compressed enough to complete an electrical circuit so a signal can be sent to the control panel to stop the gates and make them reverse.
Passive Photocells
Infra-red photocells are safety sensors that work without the physical contact required by safety edges and obstacle detection. They are installed in pairs either side of the areas to be protected. The active photocell is installed on one side of the drive or danger area. Its passive twin is mounted on the opposite side of the area the gates move through.
The active photocell emits an invisible beam onto its passive twin which is bounced back to it. If anything moves between the two photocells, the beam is broken. This triggers the gate controls to stop the gates moving before there has been any contact with the obstacle.
Carefully positioning pairs of photocells prevents anyone or anything from getting close enough to the moving gates.
This set up only requires power to the photocell that sends the beam to the passive reflector. But because of this, this type of photocells should only be used for safety and not for egress control to make self opening gates.
Active Photocells
Photocells using powered transmitter and receiver units can be used for safety and egress control.
The transmitter can be wired or battery powered to provide a range between 7 and 15m. The receiver unit always requires power by cable.
What is Needed to Turn Automatic Gates into Self Opening Gates?
Vehicle detection
As a car approaches automatic gates, something needs to recognise the vehicle and tell the gates to open. Many of the devices used for vehicle detection rely on electromagnetic induction.
If a large body of magnetic material (such as a car) passes close to a device generating an electromagnetic field, it affects that field. This change in the electromagnetic field is used to generate a signal which is sent to the gate control system instructing it to open the gates.
What Vehicle Detection Devices Are Used In Self Opening Gates?
Active photocells
A pair of active photocells can be used to make your gates open be themselves. They are installed either side of the inside of the driveway so that their beam isn’t broken by the gates when they’re open. When you want to leave, you drive up towards the gates and stop when your car breaks the beam. You are now safely far enough back from the gates while they open by themselves.
Unfortunately, if anything big enough to break the beam passes between the photocells, they will open the gates. So, this is not a highly secure solution.
Inductive loop
A loop of special cable is laid in a loop in a channel cut into the driveway. Apply current to the cable and you create an electromagnetic field. When a car enters this electromagnetic field, a signal is sent to the gate control.
Inductive loops can be used for safety and self opening gates, but they have to be installed correctly. Channels wide enough to accommodate the cable must be 50mm deep. The also need curved corners to avoid damaging the cable. Finally, they must be over 1m from any other large metallic objects.
Once the channels are dug and the cable is in position, the channel is filled with bitumen. This protects the cable from damage and makes it waterproof.
Magnetoresistive
Magnetoresitive systems work in the same way as loops but they are much smaller. A channel is cut into the driveway for a single slimline detector and its cable. The detector is small so two can be installed close together on the approach to automatic gates. With a maximum radius of 5ft, these can also be used as safety devices.
Sensitivity settings allow fine tuning to reduce interference and prevent false signals.
Other types of magnetoresistive detectors can be mounted by the side of the drive to provide an operating radius of up to 12 feet. However, cars must be moving at least 5mph to be detected so this system is only for egress control.
Other Technologies
Other technologies for detecting vehicles use ultrasonic detectors or motion detection to identify metallic vehicles.
If you like the idea of gates that magically open by themselves when you want to leave but still give you the security to keep undesirables out, we can help. We regularly retrofit egress control for self opening gates and can incorporate it into new gate automation installations.
Call us on 0800 195 1470 or email info@egrl.co.uk to find out more.
