15
14
LIGHT
OPTICAL STAGE,
A/D CONVERSION,
PROGRAMMABLE
CIRCUITRY
MICROPROCESOR
CONTROL
GRAPHICAL
DISPLAY
SIGNAL PROCESSING
SENSOR
CIRCUIT
9. SPECTRAL RESPONSE (Theory of Operation)
10. WARRANTY, MAINTENANCE
AND BATTERY REPLACEMENT
10.1 WARRANTY
The warranty policy for the AccuMAX XRP-3000A
radiometer/photometer kit is provided on the
Certificate of Limited Warranty enclosed separately
with each unit.
NOTE
: For assistance of any kind, including help
with a meter under warranty, contact the Customer
Service Department at Spectro-UV. In the United
States and Canada, call toll-free
1-866-230-7305. Include the model number, serial
number and date of purchase. If return of the unit is
deemed necessary, shipping instructions will be
provided. If an estimate of charges for nonwarranty
work or other service work is required, a quote will
be furnished upon evaluation of the unit.
Out-of-warranty service work will not be performed
without customer approval.
10.2 PREVENTIVE MAINTENANCE
•
Immediately clean all spilled materials from the
unit and wipe dry. If necessary, moisten a cloth
with soap and water to clean plastic surfaces
and the sensor head. The sensor surface should
be rinsed with ethanol to remove any residual
soap and/or organic contaminants.
•
Whenever possible, avoid exposure or use in
areas that are subject to temperature and
humidity extremes, vibration or mechanical
shock, dust or corrosive fumes, or strong
electrical or electromagnetic interference.
•
It is recommended that both the sensor detector
and the readout unit be returned to the factory
or a recognized Spectroline AccuMAX calibration
service center for a complete overall check and
recalibration
at least every 6 or 12 months
,
depending on your facility's Standard Operating
Procedures. Before returning the units to our
factory, contact the Customer Service
Department for shipping instructions.
•
When the AccuMAX is not in use, store it in a
location free from temperature extremes, dust
or corrosive fumes, and vibration or mechanical
shock.
•
If storing for an extended period, place the
AccuMAX in its carrying case after removing
the batteries.
10.3 BATTERY REPLACEMENT
•
Disconnect the sensor detector.
•
Remove the readout unit from its rubber boot.
•
Slide the battery cover to the right to expose the
internal battery compartment.
•
Carefully remove the used batteries and replace
both 9V batteries.
•
Follow the instructions for battery polarity marked
on the battery compartment.
•
Slide the battery cover back until fully in position.
•
Return the readout unit to its rubber boot
encasement.
10.4 HIGH VISIBLE LIGHT READINGS
Certain black light lamps, including the new UV-A
LED lamps, have extremely high UV intensities,
which can lead to higher visible light readings.
This can sometimes be attributed to naturally
fluorescing materials that may be present on, or
part of, meter sensors. It may also be caused by high
ambient light in the testing area. Make sure
that meter sensors are clean, serviceable and
calibrated properly. See Preventive Maintenance
for more information.
THE INPUT OPTICS
The lambertian (cosine) response of the sensor head
is desirable for many measurement applications,
especially those where the angle from the source to
the detector is variable or those situations where the
angle from the source is ''extended,'' such as in the
measurement of a fluorescent lamp at distances
comparable to or shorter than its length. In the latter
case, the extended source provides radiation from
many angles, all of which must be properly
''weighted'' as to their effectiveness on the plane
represented by the sensor surface.
In actual practice, it is difficult to make a sensor
conform to the ideal response over the entire solid
angle of 2
TT
steradians. The sensor units of the
AccuMAX meter minimize this problem by being
outfitted with optimal transmission diffusing materials
for various spectral regions. These diffusion materials
are mounted close to the surface of the sensors so
that the oblique rays are not obstructed. The spectral
range is selected by adding an appropriate UV
interference filter within the optical stack before the
sensor cell assembly.
THE SENSOR CELL
Photovoltaic Operation
When a p-n junction is operated with no externally
applied voltage, it is considered to be operating in
the photovoltaic mode. Under this zero applied
voltage condition and low levels of incident light, the
p-n junction will generate a current proportional to
the light power incident on the active surface. This
photon-induced current, or photocurrent, will divide
between the diode parallel dynamic resistance and
the parallel load resistance. The dynamic resistance
is normally a high value and is an inverse exponential
function of forward voltage. The direction of current
flow will produce a voltage across the diode that
opposes the band-gap potential of the photodiode
junction, thus forward biasing it. As a result, the value
of the diode dynamic resistance (R
d
) drops
exponentially as the irradiance increases and the
photogenerated voltage is a quasilogarithmic function
of diode irradiance when the external load resistance
is considered. Another major disadvantage is that R
d
typically has a wide spread of values over different
production batches.
One way of achieving sufficiently low load resistance
and eliminating the effect of the diode parallel
resistance is to feed the photocurrent into the virtual
ground of an operational amplifier.
The output voltage is the result of the photocurrent
being driven by the amplifier through the feedback
resistor and the input impedance R
in
= R
f
/A where A
is the open loop gain and R
f
the feedback resistor.
This circuit has a linear response and is low noise
due to the almost complete elimination of leakage
current with the zero bias. This results in a
proportional voltage being presented to the signal
conditioning section of the electronics.
