人体热释电红外传感器PIR原理

典型的例子就是

PIR

。

PIR

广泛的用在警报器上。如果你拿一个看看，你会发现 在每个

PIR

上都有个塑料的小帽子。

这就是菲涅尔透镜。

小帽子的内部都刻上了齿纹。

这种菲涅尔透 镜

可以将入射光的频率峰值限制到

10

微米左右（人体红外线辐射的峰值）。

菲涅耳透镜可以把透过 窄带干涉滤光镜的光聚焦在硅光电二级探测器的光敏面上，

菲涅尔透

镜不能用任何有机溶液

(

如酒精等

)

擦拭，除尘时可先用蒸馏水或普通净水冲洗，再用脱脂棉

擦拭 。

3.

How Infrared motion detector components work

Infrared Radiation_____________

Infrared radiation exists in the electromagnetic spectrum at a

wavelength that is longer

than visible light. It cannot be seen but it can be detected. Objects that generate heat also

generate infrared radiation and those objects include animals and the human body whose

radiation is strongest at a wavelength of 9.4um. Infrared in this range will not pass through

many types of material that pass visible light such as ordinary window glass and plastic.

However it will pass through, with some attenuation, material that is opaque to visible light

such as germanium and silicon. An unprocessed silicon wafer makes a good IR window in

a weatherproof enclosure for outdoor use. It also provides additional filtering for light in the

visible range. 9.4um infrared will also pass through polyethylene which is usually used to

make Fresnel lenses to focus the infarared onto

sensor elements.

Pyroelectric Sensors_____________

The pyroelectric sensor is made of a crystalline material that generates a surface electric

charge

when

exposed

to

heat

in

the

form

of

infrared

radiation.

When

the

amount

of

radiation striking the crystal changes, the amount of charge also changes and can then be

measured

with

a

sensitive

FET

device

built

into

the

sensor.

The

sensor

elements

are

sensitive to radiation over a wide range so a filter window is added to the TO5 package to

limit detectable radiation to the 8 to 14mm range which is most sensitive to human body

radiation.

Typically, the FET source terminal pin 2 connects through a pulldown resistor of about 100

K to ground and feeds into a two stage amplifier having signal conditioning circuits. The

amplifier is typically bandwidth limited to below 10Hz to reject high frequency noise and is

followed

by

a

window

comparator

that

responds

to

both

the

positive

and

negative

transitions of the sensor output signal. A well filtered power source of from 3 to 15 volts

should be connected to the FET drain terminal pin 1.

The

PIR325

sensor

has

two

sensing

elements

connected

in

a

voltage

bucking

configuration.

This

arrangement

cancels

signals

caused

by

vibration,

temperature

changes and sunlight. A body passing in front of the sensor will activate first one and then

the other element whereas other sources will affect both elements simultaneously and be

cancelled.

The

radiation

source

must

pass

across

the

sensor

in

a

horizontal

direction

when sensor pins 1 and 2 are on a horizontal plane so that the elements are sequentially

exposed to the IR source. A

focusing device

is usually used in front of the sensor

The figure below shows the PIR325 electrical specifications and layout in its TO5 package.

Note the wide viewing angle without an external lens.

This is a typical application circuit that drives a relay. R10 and C6 adjust the amount of

time that RY1 remains energized after motion is detected.

Download PDF drawing.

Fresnel Lens_____________

A Fresnel lens (pronounced Frennel) is a Plano Convex lens that has been collapsed on

itself

to

form

a

flat

lens

that

retains

its

optical

characteristics

but

is

much

smaller

in

thickness and therefore has less absorption losses.

Our

FL65

Fresnel

lens

is

made

of

an

infrared

transmitting

material

that

has

an

IR

transmission range of 8 to 14um which is most sensitive to human body radiation. It is

designed to have its grooves facing the IR sensing element so that a smooth surface is

presented to the subject side of the lens which is usually the outside of an enclosure that

houses the sensor.

The lens element is round with a diameter of 1 inch and has a flange that is 1.5 inches

square.

This

flange

is

used

for

mounting

the

lens

in

a

suitable

frame

or

enclosure.

Mounting can best and most easily be done with strips of Scotch tape. Silicone rubber can

also be used if it overlaps the edges to form a captive mount.

The FL65 has a focal length of 0.65 inches from the lens to the sensing element. It has

been determined by experiment to have a field of view of approximately 10 degrees when

used with a PIR325 Pyroelectric sensor.

This relatively inexpensive and easy to use Pyroelectric Sensor and Fresnel Lens can be

used in a variety of science projects, robots and other useful devices.

3.1

A.1

Focusing devices for pyroelectric infrared sensors

Pyroelectric infrared sensors

A.2

First

we

will

look

at

a

pyroelectric

infrared

sensor

and

see

how

it

is

made

and

why

a

focusing

device

is

necessary.

A

commonly

used

pyroelectric

infrared

sensor

has

two

sensing

elements

internally

connected in a voltage bucking configuration.

A pyroelectric

sensor has an

infrared filter

window that

admits IR within

the 5 to 15

micrometer

wavelength

range. One end

of the two

series-connected

elements in an

analog sensor is

connected to pin

3 that is normally

grounded. The

other end

connects

internally to the

gate of a Field

Effect Transistor

and to a very

high value

pulldown

resistor. Power is

applied to FET

drain pin 1 and

the output signal

comes from FET

source pin 2

which usually

connects

through an

external

pulldown resistor

to ground and to

an amplifier. A

digital sensor not

shown here,