Grade 3 intruder detection systems need to be able to detect attempts to mask detectors when the system is unset and prevent it from then being set while the detectors are obstructed. This functionality, set out in BS EN 50131-1, ensures that systems for use in medium to high-risk applications are resilient to tamper attempts by intruders.
Historically, anti-mask functionality makes use of either microwave technology or active infrared sensing. As with most detection technologies, both approaches have benefits, but can be susceptible to false activations in certain circumstances. Given the target applications for Grade 3 systems include higher risk commercial properties, it is imperative to ensure selected detectors offer the best anti-mask protection available.
The anti-masking used in the new range of Capture Grade 3 detectors from Texecom employs an infrared emitter (LED) and phototransistor (receiver) pair to detect masking events. This approach to active IR detection is superior to other methods. It is not only highly consistent in terms of performance but is also less prone to nuisance activations. The active IR technology has been adapted from proven solutions used in life-safety equipment produced by Texecom’s sister company, Apollo.
Phototransistors used to receive infrared signals can be impacted by the Early effect, where performance can be impacted by changes in the voltage levels. For anti-mask applications, this means if the ambient light level increases, leading to a change in the voltage level, the sensor might signal a false masking event. The ensure this common problem is eliminated, Texecom has implemented a new type of circuit: a Current Mirror. This ensures the voltage across the sensor is constant regardless of light level. The result is a significant improvement in immunity to the potential impact of ambient light.
To increase accuracy and reliability in a wide range of conditions, the main anti-masking LED flash is preceded by a smaller initial flash. This Pre-Bias Dual-Flash technology eradicates issues and ensures the anti-mask function is consistent and reliable.
To further filter out nuisance activations, Texecom makes use of an additional output from the microwave module. This microwave support is possible as the signal is distinct from alarm activations caused by objects further away in the detector’s field of view. While the microwave signal is not fully reliable, it is never used on its own to create a masking alarm, but instead provides support to the active IR technology.
Using innovative signal processing, the new Capture Grade 3 detectors from Texecom deliver highly accurate and reliable anti-mask detection, enhancing the protection on offer to medium and high-risk commercial users.