A
Analog Output: A continuous voltage signal proportional to the amount of infrared detected, as opposed to a digital on/off output.
Angular Coverage: The horizontal angle over which the sensor can detect motion, typically 90° to 180°.
B
Black Body Radiation: The electromagnetic radiation emitted by an object due to its temperature. Humans emit black body radiation peaking around 9.7 μm.
Block Time: The period after a detection during which the sensor ignores further motion, also called lockout time.
C
Common-Mode Rejection: The ability of a differential sensor to cancel signals that affect both elements equally, such as ambient temperature drift.
Curtain Lens: A Fresnel lens that creates a narrow, long-range detection pattern, like a curtain.
D
Detection Range: The maximum distance at which the sensor can reliably detect motion.
Digital Output: A binary output (HIGH/LOW) indicating motion detection.
Dual Element: A sensor containing two pyroelectric elements connected differentially.
E
EMI (Electromagnetic Interference): Electrical noise that can cause false triggers in PIR sensors.
F
False Trigger: A detection event caused by something other than intended motion, such as a heat source or electrical noise.
Fresnel Lens: A compact lens that focuses infrared onto the sensor element and defines the detection pattern.
G
Gain: The amplification factor applied to the raw sensor signal.
H
Hold Time: The duration the output remains HIGH after motion is detected, also called delay time.
Hysteresis: A built-in margin to prevent output oscillation near the threshold.
I
Infrared (IR): Electromagnetic radiation with wavelengths longer than visible light, from about 0.7 μm to 1 mm.
J
JFET: Junction Field Effect Transistor, often used as an impedance converter in pyroelectric sensors.
L
Lens: See Fresnel lens.
Lockout Time: See Block time.
M
Microwave Sensor: A motion sensor that uses Doppler radar, often combined with PIR for dual-technology detectors.
N
NEP (Noise Equivalent Power): A measure of sensor sensitivity; lower NEP means better sensitivity.
O
Open Drain Output: An output that requires an external pull-up resistor, common in some PIR sensors.
P
Passive Infrared (PIR): A sensor that detects motion by measuring changes in infrared radiation, without emitting any energy.
Pet Immune: A sensor or lens designed to ignore small animals.
Potentiometer: An adjustable resistor used to set sensitivity or delay time.
Pyroelectric Effect: The generation of an electrical voltage by a material when heated or cooled.
R
Repeatable Trigger: A mode where the hold time resets with each new motion event.
S
Sensitivity: The sensor’s ability to detect small motion or distant objects.
Shield: A metal enclosure that protects the sensor from EMI.
T
Threshold: The signal level above which motion is declared.
Time Delay: See Hold time.
V
Voltage Comparator: A circuit that compares the sensor signal to a threshold and produces a digital output.
W
Warm-up Time: The period after power-up during which the sensor stabilizes and may produce false triggers.
Wavelength: The distance between successive peaks of a wave; for IR, typically measured in micrometers (μm).
Z
Zone: A detection region created by the Fresnel lens. A PIR sensor typically has multiple zones.
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