The storage and operating temperature range of
the detectors is specified from -40°C up to +85°C.
It needs to be noted that technical data usually
reference room temperature and may vary within
the specified temperature range.
Digital Pyrodetectors –
a New Family
Pyroelectric detectors are AC type devices and
give signals upon change of received Infrared
radiation. Until today, all available detectors are
analogue, i.e. they provide an analogue signal
output. Excelitas is the first to introduce a
family of detectors which differ from previous
generations by offering a digital signal output.
With the DigiPyro® family Excelitas is offering
digital Detectors for all these applications and
1.1 Integrated Electronics
The DigiPyro® series integrates the first stages of
circuitry into the detector housing: Amplification
of the signal, then the A/D conversion, which
needs a voltage reference. Following an internal
10 Hz electrical low pass filter the serial Interface
provides for the “direct link“communication
which is a one wire bidirectional communication
feature. The whole concept is running by its own
internal oscillator, which determines the speed
of the internal process. The direct link feature
enables the user to have the host µC request
the information and its resolution, so the host
controls the communication speed.
1.2 From Analog to Digital
The DigiPyro series is the first pyroelectric detector
family to display information in Bit form as
opposed to µV signals of analogue detectors.
To give a measure for comparisons of traditional
detectors to digital versions, the rule of thumb for
signal levels versus bit information can be used:
• Resolution: 1 LSB ≙ 6.5 µV
• Noise: 6 Count ≙ 39 µV
• DC Offset 8192 Counts
• Digital Range: 0 to 16383 Counts
In a typical motion electronic application the
expected signal voltages range from 100 µV to
500 µV, so the digital signal may range about 100
bit-count on to the offset. The dynamic range of
the digital detector comprises the range from 511
counts to 15873 counts and with this it is wider
than the most application based signal levels.
Outside of this range the detectors offers an
Out-of-Range Reset function.
1.3 Digital Zero Signal Line
As the pyroelectric effect generates positive and
negative signal amplitudes, the detector circuitry
needs an electrical offset to be able to process
such signals. In all analog circuitry this value is
the offset voltage, which is usually subtracted
after the first amplifier stage.
With DigiPyros, the amplification is included
already, and the internal voltage reference
provides for the required offset. As to the user
this offset appears as a digital zero line at about
8000 bit-count, it may vary in series from one
part to the next. To recognize the zero line of
the individual detector, the user may either use
a digital band-pass or subtract the measured
offset from the signal.
1.4 The Host Needs to Filter The Signal
The DigiPyro does not include any processing
intelligence inside, unlike most analog
Pyrodetectors the DigiPyro uses a direct
communication with the hosting microcontroller
without any analog hardware filtering (only the
previously mentioned low-pass filter). Thus it
becomes necessary to implement all necessary
filtering by software filters within the hosting
microprocessor of the unit.
for Pyroelectric Detectors
Pyroelectric detectors had originally been
designed as single element types for non-contact
temperature measurement. During further
research, dual element types were developed
with multi-facet mirrors or Fresnel lenses entering
the field of motion detection, starting as passive
intrusion alarm (Burglar Alarm, PIR), followed by
automatic light switches and security lights and
lamps. The same concept is also applied with
some automatic door openers.
Today the Environment and its protection is
one of our most serious concerns. Features and
instrumentation are required to measure and
monitor all kinds of gas in our environment. One
of the methods applied is the NDIR technique, a
principle of measuring gas concentration by its
absorption properties in the infrared range. Our
detectors and sensors are a vital part of making
our environment more safe, secure and healthy.
Most of PIR Motion detecting devices have been
designed around Dual Element types, more
advanced units apply Four Element “Quad”
For Gas Sensing single element with narrow
band filters are applied in single or dual
The NEP value is a form of signal to noise ratio.
The NEP value specifies the minimum radiation
power that can be detected by the sensor, resulting
in an output that just exceeds the noise. NEP
refers to RMS values of signal and noise and in
addition to the electrical bandwidth. The lower
the NEP, the better the sensor is.
Sometimes also used for comparison of sensors,
the Specific Detectivity (D*) allows the character-
ization of sensing materials. It is defined as
reciprocal of NEP referring to the sensor area.
Details of these parameters as function of the
electrical frequency are given in Figure 6.
Responsivity, Noise vs. Frequency
R (kV/W) Noise (µVrms / √Hz)
–– Responsivity –– Noise
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