參數(shù)資料
型號(hào)： 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(yè)數(shù)： 10/76頁(yè)
文件大小： 1240K
代理商： VT900
5
Selecting a Photocell
Specifying the best photoconductive cell for your application requires
an understanding of its principles of operation. This section reviews
some fundamentals of photocell technology to help you get the best
blend of parameters for your application.
When selecting a photocell the design engineer must ask two basic
questions:
1.
What kind of performance is required fromthe cell
2.
What kind of environment must the cell work in
Performance Criteria
Sensitivity
The sensitivity of a photodetector is the relationship between the light
falling on the device and the resulting output signal. In the case of a
photocell, one is dealing with the relationship between the incident light
and the corresponding resistance of the cell.
Defining the sensitivity required for a specific application can prove to
be one of the more difficult aspects in specifying a photoconductor. In
order to specify the sensitivity one must, to some degree, characterize
the light source in terms of its intensity and its spectral content.
Within this handbook you will find curves of resistance versus light
intensity or illumnation for many of PerkinElmers stock photocells. The
illumnation is expressed in units of fc (foot candles) and lux. The light
source is an incandescent lamp. This lamp is special only in that the
spectral composition of the light it generates matches that of a black
body at a color temperature of 2850 K. This type of light source is an
industry agreed to standard.
Over the years PerkinElmer has developed different “types” of
photoconductive materials through modifications made to the chemcal
composition of the detector. For a given type of photoconductor
material, at a given level of illumnation, the photoconductive filmwill;
have a certain sheet resistivity. The resistance of the photocell at this
light level is determned by the electrode geometry.
R
H
=
ρ
H
(
w / l
)
where:
R
H
= resistance of cell at light
level H
ρ
H
= sheet resistivity of
photoconductive filmat light level
H
w
= width of electrode gap
l
= length of electrode gap
Sheet
sensitivity
(
ρ
H
)
for
photoconductive films at 2 fc are in the range of 20 M
per square.
The ratio
w / l
can be varied over a wide range in order to achieve
design goals. Typical values for
w / l
run from0.002 to 0.5, providing
flexibility for termnal resistance and maximumcell voltage.
Spectral Response
Like the human eye, the relative sensitivity of a photoconductive cell is
dependent on the wavelength (color) of the incident light. Each
photoconductor material type has its own unique spectral response
curve or plot of the relative response of the photocell versus
wavelength of light.
The spectral response curves for PerkinElmers material types are
given in the handbook and should be considered in selecting a
photocell for a particular application.
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