Perimeter intrusion detection systems (PIDS) protect properties and sensitive areas from unauthorized access using various sensors. Infrared (IR) sensors, including Active Infrared Sensors (AIS) and Passive Infrared Sensors (PIS), are key in detecting motion and environmental changes. The distinctions, benefits, and applications of each kind in perimeter security are examined in this article.
An Overview of Perimeter Intrusion Detection Systems Using Infrared Technology
Infrared radiation, which is released by objects as heat, is picked up by infrared sensors. Although this radiation is not visible to the human eye, it can be detected with specialized detectors. In a perimeter intrusion detection system, infrared sensors are used to detect movement, identify intruders, and trigger alarms or other security measures. Depending on their usefulness and design, these sensors can be either active or passive.
Active Infrared Sensors (AIS) emit infrared light or radiation and then measure the reflection or interruption of this signal. The sensor sends out a beam of infrared light and detects the return of that light, which is disturbed if something enters the sensor’s detection zone.
Passive Infrared Sensors (PIS), on the other hand, do not emit any signal. They passively detect infrared radiation emitted by objects, typically the heat from humans or animals. By detecting variations in the infrared light in their environment, these sensors are intended to identify movement.
Active Infrared Sensors (AIS)
Active infrared sensors function by emitting an infrared light signal, typically in the form of a beam, which is then reflected back to the sensor. Any object that intersects or blocks the beam causes a disruption, triggering an alert in the system. These sensors are often used in more complex and controlled perimeter environments due to their ability to detect specific disturbances and provide higher accuracy in some situations.
How Active Infrared Sensors Work
The operation of an active infrared sensor is straightforward. An infrared light transmitter is part of the sensor. This light travels through the atmosphere before hitting an object or surface. The light then reflects back to the sensor’s receiver, where it is detected and measured. If the amount of reflected light differs from the expected signal, an intrusion or obstruction is detected. The system can then send an alert or trigger an alarm.
Advantages of Active Infrared Sensors
Higher Accuracy: AIS are known for their ability to detect specific objects, such as intruders or animals, within a designated area. They are therefore very useful in settings where precise detection is essential.
AIS’s versatility allows it to be utilized in both indoor and outdoor locations. They are particularly effective in detecting large objects or individuals in motion, making them ideal for outdoor perimeter detection.
Longer Detection Range: Active infrared sensors can cover greater distances compared to passive infrared sensors. They are therefore appropriate for extensive perimeter defense.
Works Well in Low Light: Since active infrared sensors rely on emitting their own light, they function effectively in low-light or nighttime conditions, ensuring round-the-clock security.
Disadvantages of Active Infrared Sensors
Vulnerability to Environmental Factors: The performance of AIS can be affected by weather conditions such as rain, fog, or dust. These environmental factors can scatter or absorb infrared light, leading to false alarms or detection failures.
Complexity of Installation: Because precise alignment of the transmitter and receiver is required, installing active infrared sensors might be more difficult. Misalignment can lead to detection failures.
Higher Power Consumption: Active sensors consume more power due to the need to emit infrared light continuously. In places where power supplies are an issue, this can be a drawback.
Passive Infrared Sensors (PIS)
Unlike active infrared sensors, passive infrared sensors do not emit any signal. Instead, they detect the infrared radiation emitted by objects or humans. PIS are most effective in detecting warm-blooded creatures, such as humans and animals, due to the heat they emit. These sensors are commonly used in security applications for detecting movement within a specific area, such as a perimeter fence or an indoor environment.
How Passive Infrared Sensors Work
PIS operates by identifying the heat, or infrared radiation, that nearby objects release. They employ a detector composed of substances that produce an electrical signal in reaction to temperature changes, such as thermopiles or pyroelectric crystals. The sensor detects a shift in infrared radiation and sounds a warning or alarm when an animal or person walks inside its range of view.
Advantages of Passive Infrared Sensors
Low Power Consumption: PIS are energy-efficient because they do not need to emit any signal. Perfect for extended use when power consumption is a key factor.
Simplicity of Installation: PIS are generally easier to install than AIS since they do not require precise alignment between a transmitter and receiver. They can be positioned where they can efficiently sense movement.
Cost-Effectiveness: Due to their simpler design and lower power requirements, passive infrared sensors are often more affordable than active infrared sensors. They are therefore a well-liked option for a variety of perimeter security applications.
Reliable in Varied Environments: PIS are less susceptible to interference from environmental factors such as rain or fog, making them more reliable in outdoor and harsh weather conditions compared to AISs.
Disadvantages of Passive Infrared Sensors
Limited Detection Range: Passive infrared sensors typically have a shorter detection range compared to active infrared sensors. They work better in zones or smaller areas with narrower detection coverage.
Sensitivity to Small Movements: PIS are more sensitive to even small movements, which can result in false alarms triggered by small animals or environmental changes.
Limited by Line of Sight: Since PIS detects heat changes in its field of view, any obstruction in the sensor’s line of sight can hinder detection. For instance, the sensor’s capacity to detect movement may be obstructed by tall foliage or barriers.
Comparing Active and Passive Infrared Sensors in Perimeter Intrusion Detection Systems
When it comes to choosing the right infrared sensor for a perimeter intrusion detection system, several factors must be considered, including the environment, the type of perimeter being secured, and the level of security required. Below is a comparison of the two types of sensors:
| Feature | Active Infrared Sensor (AIS) | Passive Infrared Sensor (PIS) |
| Detection Principle | Emits infrared light and detects reflections | Detects infrared radiation emitted by objects |
| Power Consumption | Higher power consumption | Low power consumption |
| Detection Range | Longer range, suitable for large perimeters | Shorter range, suitable for small to medium perimeters |
| Installation | More complex installation and alignment | Simpler installation process |
| Environmental Sensitivity | Affected by weather conditions like rain, fog, or dust | Less affected by environmental factors |
| False Alarm Susceptibility | Lower susceptibility to false alarms | Higher susceptibility due to sensitivity to small movements |
| Cost | Typically higher cost | More cost-effective |
| Best Use Case | Long-range, precise detection in controlled environments | Smaller to medium-sized perimeters, outdoor environments |
Choosing Between Active and Passive Infrared Sensors
The decision between active and passive infrared sensors ultimately depends on the specific requirements of the perimeter intrusion detection system. Active infrared sensors are better suited for larger perimeters, where longer detection ranges and more precise detection are needed. They are ideal for settings where the system needs to detect specific intruders, such as large human targets, in real-time.
On the other hand, passive infrared sensors are more suitable for environments where power efficiency, simplicity of installation, and cost are the primary considerations. They are perfect for smaller perimeters or areas where environmental conditions may interfere with active sensors.
Conclusion
Active infrared sensors offer higher accuracy and longer range, ideal for high-security areas, but are more complex and sensitive to environmental factors. Passive infrared sensors are simpler, energy-efficient, and reliable in various weather conditions, though they have a shorter range and may produce more false alarms. In perimeter intrusion detection, the choice depends on factors like security needs, budget, and environmental conditions. For the best security, both are frequently used in conjunction.
