MP NaPiOn Motion Sensor on Automatic Door Opener
The NaPiOn motion sensor is product of Panasonic electronics. The automatic door opener uses the Area Reflective Type.The Area Reflective Type emits infrared rays from an LED.The sensor sens out a ray of light towards the object/human body then uses the reflected light to measure the distance and determine whether there is a person within the given distance of the sensor. When a sensor detects a person within its circumference of sight, it sets an output non-contact switch to ON. This type of sensor uses a series of complex embedded motion sensors with manually operated Program activators which are push buttons and switches,safety sensors that ensures that the doors do not get in contact with the user, Entrance control system,wireless program switch and a remote control.
Figure 1: Area Reflective Type Operation Principles
The MP NaPiOn Motion Sensor Area Reflective Type in advanced modules uses combination of photo-sensor motion detector and the passive infrared (PIR) motion detectors which are installed at a specific location just above the door.The photo sensor is composed of a focused laser beam and a light sensor. The photo-sensor and PIR motion detectors are part of a wireless sensor network device.A wireless sensor network device is a device packed data collecting component which includes a sensor and /or an actuator,a radio stack,an enclosure,an embedded processor and a power delivery mechanism.
The photo-sensor motion detector box located just above the door frame sends out bursts of Radio Frequency(RF) beams and when an object walks between the light source and the sensor,the path of the beam is temporarily blocked and a stimulus is registered in the sensor.The sensor registers a fluctuation in the levels of light and then sends a signal and the door opens.
The PIR motion detector detects infrared energy emitted from the human body. When a person walks in the detection circumference,the sensor will register a sudden increase of infrared energy. Human body body emits a certain amount of infrared energy about 9-10 micrometers around 32°C . Thus the sensor is typically sensitive in the range of 8-12 micrometers at which a signal will be sent and the door will open.The door stays open until the person is out of range at which the door closes.
The manually operated activators control; the automatic opening and closing,reduce opening width and sequence opening. It also has reset functions and maintenance indicator to notify when the door has reached its programmed number of cycles.
Safety sensors provide safety features such as electronic safety reverse,finger trap safety,photo cell safety, door speed safety and power failure safety .
NOTE: The same setting can also be utilized In a security system ,instead the sensor sends an alarm signal when the infrared energy of human levels are detected
Figure 2: Analogue and Digital output characteristics of NaPiOn Motion Sensor
Interface electronic Circuits
The sensors have a built in sensor element,amplifiers and a comparator in a three-stage architectural structure . The output from the sensor element has an extremely weak signal in passive infrared scheme and the signal has to be amplified and then converted to an ON/OFF signal with a comparator circuit before output. When a body with temperature different to ambient of the surrounding, moves into the detection field of the sensor,the sensor responds with a small AC signal.The signal is a small voltage around a DC signal that varies,it is therefore compulsory to cancel the DC part of the signal and amplify the AC part. Because the signal is affected by interference from the environment ,a noise filter is necessary.
Figure 3: Schematic of the first architectural stage
Figure 3 shows that noise is filtered by components R1 and C1,cut-off frequency of about 5 Hz. This application does not need to work at high frequency because usually we are detecting human motion. The second filter is used to cancel out the DC part of the signal, components R2 and C2 perform a high pass filter with a cut-off frequency of about 0.6 Hz. Because DC signal is not amplified,the input offset voltage of the Op-amp has no importance in this application. With a gain of just over 53, the amplification gives a signal that is higher than the noise level.
Figure 4: Schematic of Second architectural stage
In the schematic the components R6,R7,R8 and R9 to Vcc/2 sets the Op-amp common mode which allows for greater amplification of AC signal in stage 2. A factor of 10 is used to avoid limitations with the gain bandwidth product (GBP).
Figure 5: Schematic of third architectural stage
This schematic allows the user to perform a window comparator,the signal is conditioned to a go to a micro-controller. The output of the Op-amp U3 and/or U4 is in low state when a heat source is detected. Components R6,R7,R8,R9 make up the divider bridge which is used to set the voltage reference of these devices. When the voltage reference of U3 and U4 are within the Vcc range,thus no constraint on the common input common mode voltage,the window comparator works.
When the signal (Vout2) is above this reference (2.77V if Vcc=3.3V),the output of U3 is in low state-close to ground.
component U4 is used to detect when the signal is below a certain reference.In our schematic the reference is 530mV thanks to the divider bridge and the Voltage calculation is thus :
Figure 6: NAND truth table
Materials used and their suitability
The Area Reflective NaPiOn motion detector is developed by a proprietary technology for lenses,detector elements,Integrated circuits (IC’s) and mounting. It is made up Highly sensitive quad element with U-shaped slits around the four light-receiving units . It is also made up of Small multi-lens. With proprietary high precision molding technology, 16 short-focal point lenses with 5 different optical axes are integrated.
Small multi-lens: used to integrate 16 short-focal-point lenses with five different optical axes in order to reduce size.
Highly sensitive quad element: U-shaped slits formed around the four light-receiving units is to improve heat insulation,reduce element size and increase element sensitivity.
T05 metal package : encloses the circuit elements (amplifier and comparator) ,its functions includes shielding and enhancing electromagnetic capabilities
Other Uses of the MP NaPiOn Sensor
This kind of sensor is used in a wide variety of applications ranging from automatic indoor lighting systems , automatic air control louver system,On/Off smoke dispersal machine ,Automatic windmill machines,Automatic water faucets ,Automatic parking meter,Non-contact switch for the toilet and many other day to day applications.
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