Newport FPM-8220, Руководство пользователя

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April 2018 20 FPM-8220
2. The factory calibration certificate includes a table of detector response at every 10 nm.
The accuracy of power measurement via the analog output of the FPM-8220 is not a factory
specification; however, the user will find it to be stable, reliable, and useful. The following
relationship will allow the user to convert analog voltage output into power output.
=
G ∗ ( )
Where V
meas
is the voltage measured at the analog voltage output, G
r
is the gain of the
instrument when operating in range r, and ρ ( λ ) is the responsivity of the measurement head
photodiode.
The steps for converting analog voltage to power are as follows:
1. Make sure optical power input is ON.
2. Connect a voltmeter to the analog output.
3. Find the range of the instrument and then look up the gain of that range in the table
above.
4. Lookup the photodiode responsivity in the appropriate table on the measurement
head’s calibration certificate.
5. Divide the analog voltage by the product of the gain and the responsivity to get the
power.
As an example, suppose that we are trying to measure the power of a 1550nm laser. We
record the analog voltage output, V
meas
, at 3.5V. Query the instrument to determine the gain
range. In this example, the gain range is 3 so the gain is 10V/10µA. The gain value is
calculated by dividing the full scale voltage range on the instrument in combination with the
heads by the maximum current boundary of gain range 3, located on the table above. We then
go to table 1 of the calibration certificate for the measurement head
and find the responsivity of
the head at 1550nm, which is 6.0739E-3 A/W. The power of the laser is:
=
G ∗ ( )
=
3.5V
(10V/μA) ∗ (6.0739 − 3 / )
= 57.62 = −42.39