參數(shù)資料
型號： VT900
廠商： PerkinElmer Inc.
英文描述： Photoconductive Cells and Analog Optoisolators (Vactrols)
中文描述： 光導(dǎo)細(xì)胞和模擬光隔離器（Vactrols）
文件頁數(shù)： 28/76頁
文件大?。?/td> 1240K
代理商： VT900
23
Application Notes—Photoconductive Cells
APPLICATION NOTE #2
LightResistanceMeasurementTechniques
The light resistance or “on” resistance (RON) of a photoconductor cell
is defined as the resistance of the cell as measured at a special light
level using a light source with a known output spectrum Furthermore,
the cell must be “l(fā)ight adapted” for a specific period of time at an
established level of illumnation in order to achieve repeatable results.
The industry standard light source used for light resistance
measurements is a tungsten filament lamp operating at a color
temperature of 2850 K. Specifying the 2850 K color temperature for the
light source fixes the spectral output (i.e. the tungsten filament light has
fixed amounts of blue, green, red, and infrared light).
For consistency and ease of comparing different cells, PerkinElmer
lists light resistance values for its photocells at two standard light
levels: 2 fc (footcandles) and at 10 lux. The footcandle is the old,
historical unit for measuring light intensity and is defined as the
illumnation produced when the light fromone standard candle falls
normally on a surface at a distance of one foot. The lux (the metric unit
of light measurement) is the illumnation produced when the light from
one candle falls normally on a surface of one meter. The conversion
between footcandle and lux. is as follows:
1.0 fc = 10.76 lux
1.0 lux = 0.093 fc
As explained in the section on “Selecting a Photocell”, the “l(fā)ight
history” effect necessitates the pre-conditioning of the cell before a
light resistance measurement is made. PerkinElmer stores all cells at
roomtemperature for 16 hours mnimumat 30 – 50 fc (about 320 - 540
lux) prior to making the test measurement.
Sometimes the design engineer or user does not have access to the
precision measurement equipment necessary to determne the light
levels or light intensities of the application. Should this prove to be a
problem calibrated photocell samples with individual data can be
provided by PerkinElmer.
APPLICATION NOTE #3
Spectral OutputofCommonLight Sources
Incandescent lamps can be considered as black body radiators whose
spectral output is dependent on their color temperature. The sun has
approximately the same spectral radiation distribution as that of a black
body @ 5900 K. However as viewed fromthe surface of the earth, the
sun's spectrumcontains H
2
O and CO
2
absorption bands.
Black Body Sources Output vs. Wavelength
Fluorescent lamps exhibit a broad band spectral output with narrow
peaks in certain parts of the spectrum Shown below is a plot of the
light output of a typical daylight type fluorescent tube.
Fluorescent Lamp Output vs. Wavelength
Due to their long operating lifetimes, small size, low power
consumption, and the fact they generate little heat, LEDs are the light
sources of choice in many applications. When biased in the forward
direction LEDs emt light that is very narrow in spectral bandwidth (light
of one color). The “color” of the light emtted depends on which
semconductor material was used for the LED.
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