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4.5 Performing Basic Measurements
4.5.1 Power Measurements
The 1830-C’s most basic measurement mode is in the units of Watts.
Power measurements may be made with background correction, which is
initiated by pressing the ZERO key. The following equation illustrates this
relationship:
Watt reading = Net Applied Power
= ( I - I
z
) / R
where
I = detector input current
I
z
= detector background current defined
when the ZERO key was pressed
R = responsivity of the detector (A/W)
(or detector with attenuator)
a. Select the Watt measurement mode, auto-range, and a wavelength. Use
manual ranging if you want manual control of the range; over-range is
indicated by an OL message.
b. Block the light to be measured.
c. Initiate background correction by pressing the ZERO key. Display
should read approximately zero, but will fluctuate depending upon the
variations in the amount of light reaching the detector and the detector
dark current fluctuations.
d. Illuminate the detector with the optical signal to be measured.
e. Take the reading from the display.
4.5.2 Logarithmic Measurements (dB and dBm)
The 1830-C can make logarithmic measurements referenced to any mea-
sured power level or to a 1 mW power level by changing the measurement
units to dB or dBm, respectively.
NOTE
Log measurements should always be made on the lowest possible range
(without over-ranging). Readings on high ranges will not allow optimum
calculations of the logarithm. When in doubt, use auto-range.
NOTE
When using log measurements with background correction, the signal after
the subtraction of the stored offset power level may be negative. In this
case, OL will be displayed since the log of a negative number is not defined.
This will be automatically cleared when the signal becomes positive.
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