Vehicle Detection for Gates: Inductive Loops vs Radar vs Safety Photocells
Essential Security Supplies
Reliable vehicle access starts by separating four jobs that are often confused: detecting an approaching vehicle, confirming that a vehicle is still present, protecting the moving gate or barrier, and confirming that the lane is clear. Inductive loops, radar sensors, probes, and photocells can all contribute, but they do not provide the same information.
For New Zealand gate installers and integrators, the best result comes from assigning each sensor one clear purpose, documenting the controller response, and commissioning the system with the vehicles and traffic patterns that will actually use the site.
Start with the lane sequence
Before selecting hardware, draw the gate, barrier, kerbs, pedestrian paths, and expected vehicle route. Then mark the points where the controller needs a decision.
- Activation: a vehicle is approaching and may request opening.
- Presence: a vehicle is still occupying a defined zone.
- Safety: an obstruction is in a protected movement area.
- Exit request: an authorised vehicle is leaving the site.
- Passage confirmation: the vehicle has cleared a point in the lane.
A detector that is suitable for one of these functions is not automatically suitable for all of them. The gate operator instructions and site risk assessment should define how each input is used.
How an inductive loop works
An inductive loop uses a cable installed in or below the road surface and a separate loop detector. The detector monitors changes in the loop's inductance as conductive metal enters the field. When the threshold is reached, the detector changes its relay output and the gate or access controller can respond.
Elsema's current LD40 documentation confirms 12 to 24 V AC/DC supply, selectable static, pulse, and delayed output modes, and a high-sensitivity design intended for commercial and industrial use. Elsema's current catalogue lists the MD2010 as a medium-sensitivity alternative.
The Elsema MD2010 vehicle loop detector is currently active in the Essential Security Supplies range. Confirm the loop type, supply, controller input, sensitivity, and output logic for the exact installation.
Where loops work well
Loops are useful when the project needs a physically defined vehicle detection zone. Common applications include barrier presence, free exit, sequencing, and holding a gate open while a vehicle remains over a marked area.
The main installation challenge is the road surface. Loop geometry, saw cuts, feeder routing, reinforcement, adjacent loops, moisture, and pavement movement can all affect performance. If the surface is decorative, post-tensioned, recently finished, or difficult to close for civil work, an above-ground sensor may be more practical.
Commission the loop with the smallest and largest expected vehicles, different lane positions, low-speed movement, and a stationary vehicle. If motorcycles are within scope, test them specifically rather than assuming the car setup will detect them reliably.
Radar can remove the need to cut the roadway
The OPTEX OVS-02GT is a current above-ground vehicle presence sensor for gates and barriers. OPTEX describes it as a distance-measuring radar sensor that can provide vehicle activation and presence without cutting, coring, or drilling the road surface. Current manufacturer information also lists smartphone setup, two outputs, adjustable mounting, weather resistance, and improved human cancellation.
Radar is attractive for finished concrete, cobbles, leased sites, drainage-sensitive areas, and entrances where traffic disruption must be kept low. It is also easier to reach for service or recommissioning than an in-ground loop.
The trade-off is that radar performance depends on mounting position, aiming, the defined detection zone, nearby movement, and the exact traffic scene. Cross traffic, pedestrians, vegetation, trailers, vehicles stopping on an angle, and a moving gate can all change what the sensor sees. Test the full lane and save the final settings.
Probe-style vehicle detection
A compact in-ground probe can suit sites where a full saw-cut loop is not preferred. It still needs correct positioning, cable protection, controller compatibility, and realistic commissioning.
The A-PROBE vehicle detection kit is an example of this approach. Treat it as a vehicle detector for the functions approved by its current instructions, not as a universal replacement for all safety inputs.
What a safety photocell actually detects
A photoelectric safety beam creates a line between a transmitter and receiver, or between a sensor and reflector. When something interrupts that line, the controller receives a change of state. The beam does not inherently know whether the obstruction is a car, person, trolley, animal, or debris.
That makes photocells useful for obstruction detection, but they should be positioned and programmed for the assessed hazard. A single beam samples only one line across the opening and does not describe the whole vehicle or the full entrapment zone.
Loop vs radar vs photocell
| Technology | Typical role | Main design issue |
|---|---|---|
| Inductive loop | Vehicle presence, exit request, counting, sequencing | Roadway work, loop geometry, feeder routing, repair access |
| Radar sensor | Above-ground vehicle activation or presence | Mounting, aiming, zone setup, surrounding movement |
| Vehicle probe | Compact in-ground vehicle detection | Position, cable route, traffic testing |
| Safety photocell | Obstruction detection across a defined beam | Alignment, mounting height, contamination, blind areas |
A practical design sequence
- Draw the lane, gate movement, kerbs, and pedestrian routes.
- Assign one clear purpose to each required input.
- Check the gate operator instructions and project safety requirements.
- Select the sensor technology that best matches each purpose.
- Confirm supply voltage, output type, controller input, and cable route.
- Commission with realistic vehicle types, speeds, and stopping positions.
- Record settings, loop dimensions, mounting positions, and controller logic.
Commission the complete sequence
Test the system with the gate closed, opening, open, timing to close, and closing. Verify approach detection, stationary presence, passage, and the programmed response to a blocked photocell. Where fault supervision is supported, test loss of the relevant device or connection.
Repeat tests at the lane edges and with the smallest credible target. If nuisance detections are reduced by changing sensitivity or zone settings, repeat all required safety and presence tests before handover.
Frequently asked questions
Can a photocell replace an inductive loop?
Not automatically. A photocell detects an interrupted beam, while an inductive loop detects conductive metal within a defined loop area. They provide different information and should be assigned according to the required gate function.
Is radar always better because there is no road cutting?
No. Radar can reduce civil work and improve service access, but it depends on mounting, aiming, and scene configuration. A correctly installed loop may provide a more physically defined presence zone.
Can one loop open the gate and hold it open?
It can, if the gate logic, loop position, traffic pattern, and risk assessment support that design. Separate activation and presence zones often make the sequence easier to understand and test.
Do vehicle detectors replace gate safety devices?
No. Vehicle detection and entrapment protection are different functions. Use the gate operator instructions and the site risk assessment to determine the safety devices required.
Choose the sensor from the function
A dependable vehicle entrance does not start with a favourite sensor. It starts with the lane sequence. Define what the controller needs to know, then select loops, radar, probes, and photocells that make those states clear and testable.
Browse the vehicle detection and warning collection, or contact Essential Security Supplies with the gate operator model, lane dimensions, and required sequence.
Technical sources checked
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