PAL: Acronym for Phase Alternate Line, PAL is an analog video standard common in Europe. PAL video is not compatible with NTSC video.
Peltier Effect: (pronounced Pel-Tee-Aay), this is a physical effect by which dissimilar metals, when joined together, produce a voltage potential that is a function of their temperature. The Peltier effect is used in electronic thermocouples, and the same effect can be used to create a cooler by driving a voltage potential across a dissimilar metal junction. This is the basis of thermoelectric (TE) coolers that are often used to stabilize the temperature of uncooled thermal imaging detectors.
Photon: A small ‘packet’ (casually speaking) of light. The conceptual model of light as small ‘quantized’ packets is a result of Quantum Mechanical theory.
Photodetector: Broad classes of detectors which are directly able to sense and quantitatively measure light. A common example of a photodetector is the CCD camera. However, many thermal infrared imagers (particularly, uncooled imagers) are not photodetectors; they form images through sensing indirect effects of light, such as temperature changes in small sensor elements (see Bolometer and Pyroelectric Effect)
Photoconductor: A type of detector element whose conductance changes in response to certain wavelengths of light. Both photoconductors and photovoltaic detectors are commonly found in cooled, MWIR devices.
Photovoltaic: A type of detector element that produces a voltage potential across the element in response to certain wavelengths of light. Both photoconductors and photovoltaic detectors are commonly found in cooled, MWIR devices.
Photoconductive Detector: A detector with a constant bias voltage across it, which, when it absorbs a photon, the bulk resistance changes, causing a change in the current. The current change is monitored in an external circuit, and compared to calibration values to render radiometric temperature data.
Photovoltaic Detector: A detector in which absorbed photons cause a voltage potential that is measured in an external circuit, and compared to calibration values to render radiometric temperature data.
Pixel: A term commonly used to describe an element in an imaging array.
Planks’ Law: This relation describes the way in which all objects emit thermal radiation as a function of temperature and wavelength.
Predictive/Preventive Maintenance: Periodic testing and monitoring of equipment to assure that the design life of the equipment can be achieved.
Probability of Detection/Recognition/Identification: Typically, tasks such as detection, recognition, and identification are expressed in terms of a “confidence interval”, or “likelihood” (example, recognition at 1000 meters at 90% confidence).
Projected Area: The projected two dimensional area of a three dimensional object. For example, the direct shadow of a baseball would be a circle.
PtSi: Platinum Silicide, a detector material sometimes used in cooled thermal imaging detectors.
Pyroelectric Detector: A detector that detects changes in temperature. These systems typically have a rotating ‘chopper’ to produce a changing scene between the lens system and the detector.
