5. Inputs
5.1 Light Sensors
The primary purpose of the ILT1700 is to measure light.
For this reason we will address the detection input first. We
offer a full line of light detection probes which can
generally cover any application area one might have. In a
few special cases, the user may want to design his own, or
may ask us to make a special probe for his/her application.
Consult the factory for assistance in that area.
5.1.1 International Light Detectors
Light sensors are generally designed for a band of
wavelengths, and for a range of magnitude. The ILT1700 has
one of the widest dynamic ranges of any instrument
available. It can span 10 decades change in irradiance
levels, which is equal to or greater than most detectors. By
using attenuators, such as the QNDS-3, the dynamic range is
pushed up by a factor of 1000 to handle very intense
sources. By using a SHD high gain detector or hig h gain
lens (L30) the system can be made more sensitive by a factor
of 100.
The SED series detectors were also designed to handle
hostile environments. The housing is machined aluminum,
which forms a rugged case.
“O”
ring grooves are designed
in to offer a sealed option for dirty environments, and for
underwater applications. The underwater model (prefixed
with SUD) comes with a 30 meter (100 feet) cable and is
pressure tested for 40 meter underwater depth.
The most popular detector is the SED033. This is a
silicon detector which has a 33 square millimeter receiving
surface, and quartz windows to make it usable down to 200
nanometers wavelength. It is specially made to optimize the
dynamic range by maximizing the internal shunt resistance,
and by minimizing the series resistance, to enhance low
level detection and high current linearity, respectively. The
large area makes it usable for optical power detection from
lasers and fiber optics, as well as to increase its sensitivity
for irradiance and illuminance measurement s.
Two vacuum photodiodes (SED240 and SED220) are
also very popular for their ability to exclude infra-red, and
for their low noise in D.C. operation. A vacuum photodiode
does not have 1/F noise, common with all semiconductors.
Also, the leakage current is much lower than semiconductors.
The light sensing surface has a lower sensitivity, but by
making a larger receiver, the sensitivity is recovered, without
excessive leakage current. The
‘sola
r blind
’
SED240(usable
band 200-320) and SED220 (165-320 nm) have the desirable
property of rejecting all energy above 320 nanometers. This
feature offers short wave detection, even in the presence of
abundant long wave radiation. The SED005 UV-Visible
GaAsP Detector extends the detection from the short wave
UV through the UVA band up to the red portion of the
visible(250-675 nm), and yet rejects the infra-red.
For very flat response and long wave detection, we offer
the SED623 thermopile detector, which has a built in
preamplifier, to transform the tiny light induced voltage
signal into an amplified current compatible with the input of
the ILT1700. The dynamic range of a thermopile is limited
to 4 decades (2e
-5
to 5e
-1
watts per square cm), but the
extremely flat spectral response from 200 to 3000
nanometers, often offsets this range limitation.
The full line of detectors offered by ILT covers spectral
ranges from 160 nm out to 40,000 nm. All of which can not be
covered in this brief review. Please contact the factory for
assistance with your requirements.
5.1.2 User and Custom Detectors
The detector input port has been designed to be
compatible with many types of input devices other than light
sensors. Other devices for measuring current, humidit y,
temperature, nuclear radiation sound levels, weight, etc., are
all possible attachments. The 15 pin
‘D’
connector has
several bias voltages available, as well as the front panel
controlled 5 volt bias. The system measures negative current
(positive electron flow) on pin 6. The return path for the
current can be either instrument signal ground (pin 7) or the
-9 volt bias available on pin 1. In either case if the front
panel bias is selected (5 V BIAS), the input voltage will be
raised by 5 additional volts. In other words, if you chose to
put the return line to the ground pin 7, the input will rise up
to +5 which will reverse bias the input device by 5 volts.
This feature also makes it possible to work with photo-
conductive devices such as cadmium sulfide or cadmium
selenide, by measuring the photoconduct ance. If the -9 Volt
bias is the return, and the 5 V BIAS is selected, there will be
a net total of 14 volts across the sensor. To minimize
leakage current in a coaxial cable, we provide a
‘guard’
pin
called
‘bia
s
common’, locate
d on pin 9. This always stays at
the same potential as the input pin 6, to minimize cable
leakage, even if the actual detector is reverse biased. Be
careful not to connect this to ground, since this point is
elevated to +5 volts when the 5V BIAS button is pressed.
In addition to these sensor related pins, we have made
+5 volts and +15 volts available for other specialized
preamplificatio n circuitry, and for other accessory probes.
No more than 10 milliamps should be drawn from +15, 5
mA from -9, and less than 50 mA from +5.
I will give an example of the hookup for a two wire
silicon detector, since that is the most likely device to be
used by a customer. The cathode should go to the input pin
6, the anode and the shield of the coaxial cable should be
connected to pin 7. With the 5V BIAS off, the detector will
operate in the photovoltaic mode. With the 5V BIAS on, the
detector would be reverse biased by 5 volts. For more
specific assistance with hooking up a special user device,
please contact the factory.
18
代理美国International Light辐照计http://www.testeb.com/yiqi/ilt/zhaoduji.html 深圳市格信达科技 电话18823303057 QQ：2104028976
