True NEGATIVE: Seems quite obvious at first glance. Is it the opposite of True POSITIVE? Simply put, the motion detector should not detect a person in its detection zone who is not in the room. But what about a seated person who is not moving? In this case, a motion detector is actually called True NEGATIVE. In practice, a distinction is made between presence sensors (typically used in offices) and motion sensors. This explains that the motion sensor, unlike the presence sensor, does not react to a sitting person. On the other hand, it has a greater range and less expensive components.
Further there are two fields False POSITIVE (phantom detections) and False NEGATIVE (blindness). Both cases describe a malfunction of the sensor. The product owner and the development partner must agree on the degree to which such malfunctions are permissible. This delimitation is very individual and can have an influence on development and product costs. For example, additional sensor technology may be required to reliably detect specific special cases. Whether the application accepts the extra price of the additional principle is ultimately up to the product owner's price-performance assessment.
The interaction of many disciplines in the implementation
In the technical implementation of a sensor application, many specialist areas come together: analog design, digital filtering and signal processing, EMC immunity, power management, communication connections, alignment and calibration, etc. All these areas require appropriate expertise, infrastructure and tools to design the adaptation to customer-specific solutions based on existing technology building blocks. STEINEL has specialized in the field of PIR, high-frequency and optical sensors and has become the market leader. Its experience and resources in hardware and firmware development, PCB design, mechanical development, application testing and manufacturing and process know-how are correspondingly extensive.
A sensor usually contains an analog circuit. This already makes the PCB a tailor-made component. For this purpose, the PCB designer works out the optimal layout in close coordination with the hardware developer. Furthermore, the sensor must be protected from environmental influences and makes demands on its assembly - due to the technology or as defined by the product owner. These aspects flow into a mechanical design, which in turn entails requirements for production processes. Here, the interaction between design and production is a central process that should not be underestimated and which eliminates critical interfaces in a solution developed and produced inhouse.
The firmware is a very central part in a sensor. Analog sensor signals are digitally converted and filtered and processed in a microcontroller. In autonomous sensors, the firmware processes the information from the sensor and controls an actuator, for example a valve for a washbasin fitting.
In a networked application, the sensor information is made available to a higher-level system via an interface. This allows spatially distributed sensors to provide much more complex detection behavior. With the wide range of communication technologies, sensors have evolved strongly in the direction of IoT (In-ternet of Things) in recent years. A wide range of implemented solutions allows STEINEL to select the right technology for a variety of use cases.
Sensors powered by a battery should function autonomously over a long period of time. Low-power applications are the rule today. Battery management can be just as much a part of this as sophisticated powersaving tricks.
Another discipline that should not be underestimated is the standard-compliant implementation and certification of the product. With a sensor, EMC immunity is always considered a critical area. STEINEL Solutions uses inhouse pre-compliance tests in its own EMC laboratory to optimize the False POSITIVE and False NEGATIVE. The solution often lies in clever signal processing in the firmware, which ultimately also results in cost neutrality for the product. Close coordination between hardware and firmware development is crucial for an optimum overall solution.