Pir sensor

A passive infrared sensor (PIR sensor) is an electronic sensor that measures infrared (IR) light radiating from objects in its field of view.

Principle of Operation

All objects with a temperature above absolute zero emit heat energy in the form of radiation. Usually this radiation is invisible to the human eye because it radiates at infrared wavelengths, but it can be detected by electronic devices designed for such a purpose.

The term “passive” in this instance refers to the fact that PIR devices do not generate or radiate any energy for detection purposes. They work entirely by detecting the energy given off by other objects. It is important to note that PIR sensors don't detect or measure "heat" per se; instead they detect the Infrared radiation emitted from an object which is different from but often associated/correlated with the object's temperature (e.g., a detector of X-rays or gamma rays would not be considered a heat detector, though high temperatures may cause the emission of X or gamma radiation).

Construction

Infrared radiation enters through the front of the sensor, known as the 'sensor face'. At the core of a PIR sensor is a solid state sensor or set of sensors, made from pyroelectric materials—materials which generate energy when exposed to heat. Typically, the sensors are approximately 1/4 inch square (40 mm2), and take the form of a thin film. Materials commonly used in PIR sensors include gallium nitride (GaN), caesium nitrate (CsNO3), polyvinyl fluorides, derivatives of phenyl pyridine, and cobalt phthalocyanine. The sensor is often manufactured as part of an integrated circuit.

Operation

What is definitely detected is the broken field for a “normal” temperature. The sensor detects the change in the infrared radiation and triggers an alarm if the gradient of the change is higher than a predefined value. The field does not have to be broken by an object with a different temperature in order to register change, as highly sensitive sensors will activate from the movement alone.

PIRs come in many configurations for a wide variety of applications. The most common models have numerous Fresnel lenses or mirror segments, an effective range of about ten metres (thirty feet), and a field of view less than 180 degrees. Models with wider fields of view, including 360 degrees, are available—typically designed to mount on a ceiling. Some larger PIRs are made with single segment mirrors and can sense changes in infrared energy over one hundred feet away from the PIR.

Differential detection

Pairs of sensor elements may be wired as opposite inputs to a differential amplifier. In such a configuration, the PIR measurements cancel each other so that the average temperature of the

field of view is removed from the electrical signal; an increase of IR energy across the entire sensor is self-cancelling and will not trigger the device. This allows the device to resist false indications of change in the event of being exposed to brief flashes of light or field-wide illumination. (Continuous high energy exposure may still be able to saturate the sensor materials and render the sensor unable to register further information.) At the same time, this differential arrangement minimizes common-mode interference, allowing the device to resist triggering due to nearby electric fields.

However, a differential pair of sensors cannot measure temperature in this configuration, and therefore is only useful for motion detection.

Product design

The PIR sensor is typically mounted on a printed circuit board containing the necessary electronics required to interpret the signals from the sensor itself. The complete assembly is usually contained within housing, mounted in a location where the sensor can cover area to be monitored.

The housing will usually have a plastic "window" through which the infrared energy can enter. Despite often being only translucent to visible light, infrared energy is able to reach the sensor through the window because the plastic used is transparent to infrared radiation. The plastic window reduces the chance of foreign objects (dust, insects, etc.) from obscuring the sensor's field of view, damaging the mechanism, and/or causing false alarms. The window may be used as a filter, to limit the wavelengths to 8-14 micrometers, which is closest to the infrared radiation emitted by living animals.

Geared DC Motor

Gear motors are complete motive force systems consisting of an electric motor and a reduction gear train integrated into one easy-to-mount and -configure package. This greatly reduces the complexity and cost of designing and constructing power tools, machines and appliances calling for high torque at relatively low shaft speed or RPM. Gear motors allow the use of economical low-horsepower motors to provide great motive force at low speed such as in lifts, winches, medical tables, jacks and robotics. They can be large enough to lift a building or small enough to drive a tiny clock.

Geared DC motors can be defined as an extension of DC motor. A geared DC Motor has a gear assembly attached to the motor. The speed of motor is counted in terms of rotations of the shaft per minute and is termed as RPM .The gear assembly helps in increasing the torque and reducing the speed. Using the correct combination of gears in a gear motor, its speed can be reduced to any desirable figure. This concept where gears reduce the speed of the vehicle but increase its torque is known as gear reduction.

External Structure

At the first sight, the external structure of a DC geared motor looks as a straight expansion over the simple DC ones.

Picture credits: http://www.engineersgarage.com

The lateral view of the motor shows the outer protrudes of the gear head. A nut is placed near the shaft which helps in mounting the motor to the other parts of the assembly.

Also, an internally threaded hole is there on the shaft to allow attachments or extensions such as wheel to be attached to the motor.

Operation Principle

Most synchronous AC electric motors have output ranges of from 1,200 to 3,600 revolutions per minute. They also have both normal speed and stall-speed torque specifications. The reduction gear trains used in gear motors are designed to reduce the output speed while increasing the torque. The increase in torque is inversely proportional to the reduction in speed. Reduction gearing allows small electric motors to move large driven loads, although more slowly than larger electric motors. Reduction gears consist of a small gear driving a larger gear. There may be several sets of these reduction gear sets in a reduction gear box.

Speed Reduction

Sometimes the goal of using a gear motor is to reduce the rotating shaft speed of a motor in the device being driven, such as in a small electric clock where the tiny synchronous motor may be spinning at 1,200 rpm but is reduced to one rpm to drive the second hand, and further reduced in the clock mechanism to drive the minute and hour hands. Here the amount of driving force is irrelevant as long as it is sufficient to overcome the frictional effects of the clock mechanism.

Torque Multiplication

Another goal achievable with a gear motor is to use a small motor to generate a very large force albeit at a low speed. These applications include the lifting mechanisms on hospital beds, power recliners, and heavy machine lifts where the great force at low speed is the goal.

Many Applications

What power can openers, garage door openers, stair lifts, rotisserie motors, timer cycle knobs on washing machines, power drills, cake mixers and electromechanical clocks have in common is that they all use various integrations of gear motors to derive a large force from a relatively small electric motor at a manageable speed. In industry, gear motor applications in jacks, cranes, lifts, clamping, robotics, conveyance and mixing are too numerous to count.

Sealed lead acid battery

A VRLA battery (valve-regulated lead–acid battery), more commonly known as a sealed battery or maintenance free battery, is a type of lead–acid rechargeable battery. Due to their construction, they do not require ventilation, can be mounted in any orientation, and do not require constant maintenance.The reduced venting is an advantage since they can be used in confined or poorly ventilated spaces.[2] They are widely used in large portable electrical devices, off-grid power systems and similar roles, where large amounts of storage are needed at a lower cost than other low-maintenance technologies like li-ion.

Some facts:-

Are less reliable than flooded lead acid Have shorter recharge time than flooded lead-acid. Cannot tolerate overcharging: overcharging leads to premature failure. Have shorter useful life, compared to properly maintained wet-cell battery. Discharge significantly less hydrogen gas. AGM batteries are by nature, safer for the environment, and safer to use. Can be used or positioned in any orientation.