Saturday, August 13, 2011

PIR325 with FL65 Fresnel lens

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 incoming radiation to the 8 to 14µm range which is most sensitive to human body radiation.

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 as shown in figure 2 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.

- Power supply: 2,5 V - 15V.
- Output: 3900 mVpp.
- Offset Voltage: 1.0 V.
- Spectral response: 5-14 um.
- Noise: 20 uVpp.
- Fresnel lens (FL65): 0.65-inch focal length & transmission range 8-14 um.