occp sensor

8/8/2019 Occp Sensor

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OCCUPANCY&

PHOTOSENSORS


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OCCUPANCY SENSORS

SWITCHING DEVICE

PRESENCE AND ABSENCE OF PEOPLE

IN THE SENSORS FIELD OF VIEW

MOTION DETECTOR + POWER SUPPLYUNIT + RELAY


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OPERATION


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Controller Functions

SENSITIVITY OF SENSOR TO MOTION

TIME DELAY

LUX CONTROL


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SENSOR SENSES MOTION

GIVES ELECTRONIC SIGNALS TO CONTROL UNIT

CONTROLLER DECIDES ABOUT OCCUPANCY STATUS

CONTROLLER ENERGISES / DE-ENERGISES RELAY

RELAY CONTACTS OPERATE LUMINAIRE


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TYPES OF SENSORS

ULTRASONIC

PASSIVE INFRA RED (PIR)

DUAL (ULTRASONIC + PIR)

ACOUSTIC


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PASSIVE INFRA RED (PIR)React to the infrared heat energy

emitted by people

Employ a Pyro-electric transducer

to detect infrared radiation whichconverts the IR energy into avoltage signal

They are called Passive devicesas they only detect radiation,they do not emit it


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A many faceted lens surrounds the transducer and focusesheat energy onto the detector.

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The lens views the area with a multitude of narrow and discrete beams or cones (does not

view the area in a continuous fashion)

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The detection pattern of PIR sensors isfan shaped, forming "fingers" of detection.

Each finger is a cone of heat detection"seen" by a segment of the detector'sfaceted lens.

There are gaps of coverage betweenadjacent fingers which widen with distance.

Since the sensor is most sensitive tomotion that moves from one sensing cone

to another, its sensitivity decreases withdistance as the gaps between sensing coneswiden


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DETECTION PATTERN



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They are strictly line-of-sight devices

They cannot "see" around corners and a

person will not be detected if there is anobstruction, such as a partition, betweenthe person and the detector


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PIR

PIR sensors are less susceptible to falseONs than ultrasonic sensors.

In addition they are better in

applications where it's desirable todetect occupancy in only a portion of aspace.

PIR detectors can be effective in spaceswith ceilings up to 20 ft or more


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Sensor coverage diagram

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ULTRASONIC

A quartz crystal emits ultrasonic wavesthroughout the space

The unit then senses the frequency of thereflected waves

If there is motion, the reflected wave'sfrequency will shift slightly

This change in the ultrasonic waves frequencyis detected as motion in the space


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A person, or any object in the room, reflectswaves emitted by the occupancy sensor.As a person moves in the space, the

frequency of the waves reflected off theperson changes. The occupancy sensordetects this change in frequency and reactsby switching on the lamps.


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ULTRASONIC

Operate at frequencies higher than thenormal human ear can detect to avoidpossible incompatibility with other devices(such as hearing aids)

Most modern ultrasonic sensors operate atfrequencies 32 kHz or higher


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ULTRASONIC

The ultrasonic sound waves cover theentire area in a continuous fashion.There areno blind spots or gaps in the coveragepattern. They can also detect movement

behind some barriers. For this reason,ultrasonic sensors may be more effectivein detecting occupancy than PIR-baseddetectors


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ULTRASONIC

Ultrasonic sensors are more sensitive to false ONsthan PIR detectors. A false ON occurs when anoccupancy detector switches on lighting when thespace is not occupied. False ONs are caused by

motion in adjacent spaces, by air turbulence nearair diffusers and open windows, and by hangingobjects in the space. Most ultrasonic sensors workbest in spaces with ceilings below 14 ft but there

are some that can detect a moving person from aheight of 30 ft or more.


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Special Features of

Occupancy SensorsManual ON mode

Automatic modeAuxiliary contacts

Annunciators and warning signals

Fail ON function

Masking labels


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Manual ON Mode

While most occupancy sensors are capable ofswitching lights on as well as off, it's oftendesirable to deactivate the automatic ONfeature so that the lights switch on only if theoccupant chooses it. This mode is also calledmanual ON/auto OFF.

Most modern sensors allow the occupant toturn lights off manually whether they remain inthe space or not


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Automatic Mode

Automatic mode turns lights on uponoccupancy and off upon vacancy.


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Auxiliary Contacts

An extra switch or set of contacts so

that more than one load can becontrolled by a single occupancy sensor.

An extra set of contacts can be used to

switch an HVAC load, an exhaust fan,or provide a contact closure to abuilding management system.


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Annunciators and Warning Signals

Detection status using an LED built into thesensor

Alarm shortly before extinguishing the lights.

{This reminds an occupant to move or wave

an arm to prevent the lights from beingswitched off }


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Annunciators and Warning Signals

This is useful for situations when theoccupant may remain unusually still for aperiod of time, or for applications where thesensor's sensitivity has been calibrated to

respond only to stronger movements.

This feature is particularly important forsensors that are operated in the manualON/automatic OFF mode if no grace period isincluded.


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Fail ON Function

Sensors with this feature keep the lights on ifthe sensor fails.


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Masking Labels

PIR occupancy sensors often have maskinglabels that allow the installer to fine-tune thecoverage range of the sensors in

applications where extraneous motioncauses a sensor to false trigger ON.


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Masking LabelsFor example, if an open door leads to a hallway

within the sensor's line of sight, a masking labelcould be used to deaden the sensor's response inthe direction of the doorway.

A preferable method is to accomplish this

electronically by reducing the sensitivity,automatically, when a room is vacated so thatmotion in the hallway will not be detected.

When a person steps across the threshold, thelights are turned on and the sensitivity isautomatically increased to its original setting.


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PHOTOSENSOR


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The photo-sensor automatically measures thelight level within or entering the controlled

building space.

The photo-sensor generates an electric signalbased on a sampling of the light in the space.The particular geometry of the photocell and itshousing determines the sensitivity of the cell to

light from different directions.


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Controller

The control unit translates the photo-sensor

signal into a command to the dimming orswitching control unit. The design of its controlalgorithm, dead bands and delays determineits responsiveness to varying lighting

conditions.


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Photo-sensor Types

Photodiode Type:

produces a voltage that is directly

proportional to the detected light

Photoconductive Type:

produces a voltage that is inverselyproportional to the detected light in a

roughly exponential relationship


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PhotoconductiveType:

Photoconductive sensors are lessexpensive than photodiodes, they arevery non-linear in response andtherefore much less accurate .

Because of their limitations,photoconductive sensors are usedprimarily in controlling nighttime outdoorlighting and indoor switching applicationsthat do not require precise light level

control


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Photodiode Type:Photodiode controls should be used inswitching and dimming applications wheremore precise light level control is important.


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Lighting When You Need

Presence Detected Insufficient

Daylight Lights ON

Presence detected sufficient

Daylight Light RegulatedAbsence Detected Lights Off


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THANK YOU

occp sensor

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