Photocells or Photo Electric Beams are basically a point to point beam of invisible infra red light that passes from a transmitting unit to a receiving unit and if an object blocks the light you know something's there. These are used with automatic gates on either side of a driveway as a safety device to prevent a gate closing on a vehicle. Normally used when a gate is set to close by itself after a time delay automatically (auto-close).

King V30 Safety PhotocellsMade by King but can be used with all 24V automatic gate operators accept for Nice Slight, Robus, Run, Titan or Toona gate operators that use the two wire Blueus system. Range Up to 15m.each $95.00 READ MORE Centsys i5 Safety PhotocellsMade by Centsys but can be used for any automatic gate operator except for Nice Slight, Robus, Run, Titan and Toona that use a two wire Bluebus system. Has a wide anlge for easy setup and range up to 40m.each $114.70 READ MOREDace PhotocellsMade by Dace but can be used for any automatic gate operator accept for Nice Slight, Robus, Run, Titan and Toona that use a two wire Bluebus system. Has a wide angle for easy setup and range up to 40meach $89.99 READ MORE

Point to Point verses Reflector 

Photocells that have a point to point infra red light beam from a transmitter to a receiver at either side of a gateway are preferred for use with gates than ones with a reflector because reflector types tend to not work as well in the rain or with sun shining on them. Although there is a reflector type that works with an Infra red Laser that is a lot better. 

Alignment

The most important thing when installing Photocells is to make sure they are facing each other. The beam of light coming from the transmitter is quite narrow so if not aimed at the receiver properly it may not work or worse still only just works and then as soon as there is some rain will stop working leaving the gate open.

Height of the Photocell

The height of the Photocell is important, if too high it may pass through car windows or go right over an empty trailer, if too low it may go under a vehicle, which may cause the gate to operate erratically. Around 600mm from the ground is a good height for cars, vans, utes, small trucks and trailers. 

If a gate is shared by larger trucks then two sets of photocells at different height are necessary.  One at 600mm and another at 900mm usually works well.

Swing Gates Require Two or Three Sets of Photocells

For swing Gates you need at least two sets of Closing Photocells to get proper coverage. Double swing gates are better than singles when using Photocells because the distance between the inside and outside set of photocells is less, where as if you have Photocells on a 4m swing gate, the distance between Photocells must NOT be more than 4m, so if you get a really short car stop between Photocells, the gate still could close on it. It's best to place the Photocells as close to the gate as possible to reduce the chance of this happening.

It is also recommended that a third set of opening photocells are installed past the gate in the open position to prevent the gate opening on a vehicle if a car is in the path of the opening gate.  A vehicle may be parking in the way so if the opening photocell is broken the gate won't open, so won't hit the vehicle.   

Photocells can Control Closing of the Gate 

Photocells can be used to control the closing of the gate if the control unit for the gate has this option, that is once a vehicle has passed through a gate it will close behind it to help prevent other vehicles following through.  This closing only occurs once a vehicle clears the photocell and can either close the gate instantly or be delayed.  The Photocell delay may be different to the auto-close delay.

Installing Photocells

For point to point photocells you do need a low voltage cable across the driveway.  With sliding gates this is usually simply a matter of installing the cable inside the gate track, if it is hollow, although care must be taken that the cable doesn't get damaged where it enters the track and that the track doesn't have any gaps between it and the driveway large enough for the cable to slip into and be crushed by the next car that drives over it. The photocells can be installed on the gate posts and if these are hollow metal posts cabling can be run inside the post.

For swing gates low voltage cable will need to be run along each side of the driveway as well as across the driveway.  One set of photocells will need stand alone posts.

READ MORE about installing low voltage cabling

Vandal Proofing Photocells

If photocells are exposed to a lot of walk past traffic the odds that they will be vandalized increases, although if they are small unobtrusive photocells that have a thicker casing this will keep this to a minimum. A metal cover can also be used with a hole in it for the infra red light.  A mesh cage is not so good because vandals can still poke things through the holes and damage the photocells.  A metal box is best because the vandals can't see what's inside reducing their interest level because they like to see it break.

Photocells for Solar Powered Automatic Gates

Photocells can be used with Solar Powered Automatic Gates so long as the power to the photocells can be turned off when the gate is not in use otherwise they will run the battery flat unless a large enough battery, solar panel and charge controller is used.  

If the gate operator has a light output or open indicator output of some sort this can be used to provide power for the photocells when the gate is opened, although must be used with the auto-close feature otherwise if the gate is left open for too long the battery will run flat or if power to the photocells time out when the gate is open it will not close.

How they are Connected

Photocells are connected to the control unit of an automatic gate. There is normally an input dedicated to Photocells although with most Nice Motors they have a Blue Bus that is a simple two wire system for connecting a Blue Bus Photocell. You must use a Blue bus Photocell with Nice Motors that have this feature.