Sensing a need for savings

Passive infrared ( PIR ) sensors offer a cost effective motion sensing solution for a wide range of applications and can be used to provide energy savings, for example, in the operation of lighting or power in areas such as warehouses, corridors and isolated rooms.Richard Thornton,MD of Panasonic Electric Works UK, explains

Passive infrared sensors offer simple, cost effective motion detectors that can be mass-produced for use in a wide range of applications. They use electromagnetic radiation in the low infrared spectrum in which radiation emitted by human movement is identified using a PIR detector. Objects that are located within the area of sensitivity generate electromagnetic radiation in the low infrared range and project an image through the focus line of the sensor onto the internal heat-sensitive element. The signal processing electronics then convert the images into electrical signals.

If the heat image remains the same, the output signal of the sensor remains unchanged. If the heat image changes, because the object moves within the area of sensitivity, the optical imaging changes accordingly. This movement results in a change of the output signal that in turn can be evaluated by a window comparator that specifies upper and lower thresholds.

Panasonic has a wide range of PIR sensors including the NaPion and PaPir ranges that offer motion detection of objects up to 12m away from a unit measuring 20mm and taking less than 1µA standby current. The PaPir sensing elements contain lithium tantalite and are lead free. The PaPir sensors were developed around a specialised circuit that allows the reduction of current consumption after motion is detected. The reduction of consumed energy allows battery life to be reduced, especially important in remote wireless or energy sensitive applications.

Panasonic has found that lighting controls companies are among the most prolific users of its PIR device. The NaPion and PaPir sensors are easily integrated into a circuit.

Many PIR sensors are supplied with separate components for the sensor, the amplifier and the comparator leaving the design engineer to circuit design, match the components and mount the unit onto a PCB. The NaPion and PaPir sensors however, have all of these circuits enclosed in one device leaving the designer with the simple task of supplying the power and connecting the output to a suitable driver circuit.

All the components are enclosed in a single shielded housing in a TO-5 style case, so the MP sensor is more tolerant to external interference from sources such as mobile phones. This greater shielding and high signal to noise ratio can help prevent false triggering and mis-operation of the control circuit.

Recent applications have include lighting control in pub and restaurant bar refrigerators that have glass doors to display bottles and cans. Here, refrigeration needs to take place constantly but the interior light does not always need to be on. Typically, however, in this type of refrigerator the light does not automatically go off when the door is closed. To ensure that the light is always on when required, a PIR sensor has been mounted within the front edge of the unit and when bar staff walk past it at regular intervals the light will stay on. However, once the bar has closed the light will turn off after a preset time. This saves power both in lighting and in the refrigerator not having to deal with the excess heat given off by the lamps when the bar is not in use.

Further applications can be illustrated by a large museum which was concerned with the amount of energy wasted in keeping display cases and their contents illuminated when no patrons were present. To solve the problem an MP sensor was mounted into display case frames to ensure exhibits are only lit when a visitor approaches.

Another use within this field has been to activate and track patrons along a series of plasma video displays to continue the information exchange while continuing along an exhibit.

Due to their high performance and low cost, the NaPion and PaPir sensors are suitable for energy and security management applications, including access control, door intercom systems, Intelligent light management, automatic control of air conditioning and ventilation systems, lighting in and around vending machines and public telephones and ATMs.

Panasonic offers free technical support and product samples to allow designers with possible applications to fully evaluate the range of PIR products and decide on the most beneficial solution to their particular requirements.