23
Manual ranging is often useful when using the audio
output or analog output features of the Model 840-C.
3.4.13 Wavelength
When the
WAVELENGTH
up or
down rocker switch
is depressed, the wavelength display increases or
decreases. The speed with which the display scrolls rises
as the key is held down longer. Adjustment in 1nm
increments is possible by momentarily pressing the
WAVELENGTH
key. The Model 840-C adopts the calibra-
tion value appropriate for the wavelength displayed and
the state of the
, ATTENUATOR
annunciator.
NOTE
If WAVELENGTH key is pressed until the wavelength
display exceeds the calibration spectrum of the sen-
sor, the wavelength display indicates “- - -”. In this
mode, the value displayed is the electrical current.
Basic measurement techniques for using the Model 840-C
to measure DC and peak-to-peak optical power are
covered in the following sections. Also included are
methods of background correction, ratio measurements,
making measurements in decibels (dBm and dB) and
using the store and recall of reference power.
In general, absolute accuracy is limited by the accuracy of
the detector calibration and environmental factors
affecting the detector. See the appropriate detector
manual for this information. Further discussion on these
topics for Newport detectors is found in Section 2.5 of this
manual.
3.5.1 Setting the Wavelength
In order to obtain accurate optical power measurements,
it is necessary to set the instrument calibration wave-
length to the wavelength of the light incident upon the
photodetector. This instrument calibration wavelength is
indicated in nanometers in the lower right hand side of
the digital LCD display and is followed by the annunciator
nm
. Upon power-up, the wavelength will be the last used
value. To change the wavelength, perform the following:
a.
Determine the wavelength of the light being meas-
ured to the nearest
nm
. If the source is broadband,
use either a value near the center wavelength of the
light or the wavelength with greatest intensity.
3.5
Performing
Basic
Measurements
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