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The sensors have a built in sensor element,amplifier 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.
Figure 3: Rating of the Sensor
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
Figure 7Figure 4: Different Types of NaPiOn Motion Sensors
Figure 58: Digital Output of NaPiOn motion Sensors
Figure 69: Analog Output of ‘NaPiOn’ Motion sensor
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FINDING MORE INFORMATION ABOUT NaPiOn Sensors [30-04-2015] :
1.Power Consumption
Materials used and their suitability2.Materials used
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.
2.1 suitability of the material
2.2 Properties
https://wiki.metropolia.fi/pages/editpage.action?pageId=103254810
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
REFERENCES
References
1. KONE Automatic Sliding Door offering.2015. SD series
URL: http://cdn.kone.com/www.kone.fi/Images/kone-slidingdoors-technical-datasheet.pdf?v=2 [ONLINE]
Accessed 30 March 2015
2. How Stuff Works.2015.Motion Detectors
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URL:http://www.avnet-abacus.eu/fileadmin/user_upload/Products_Menu/Panasonic%20Electric%20Works/Panasonic_NaPiOn.pdf [ONLINE]
Accessed 7 May 2015
6. MP Motion Sensor
URL: http://www3.panasonic.biz/ac/e/control/sensor/human/napion/rating-performance/index.jsp [ONLINE]
Accessed 7 May 2015