Chassis Ground; Analog Output (Bnc); Gain Range Boundaries; Table 2.1 Gain Range Boundaries - ILX Lightwave FPM-8200 User Manual

2
C H A P T E R

Chassis Ground

For your convenience, a chassis-ground post connector is located on the FPM-
8200's back panel. This connection point is electrically identical to the earth
ground through the AC power line third pin.

Analog Output (BNC)

A BNC output connector is provided to give you direct access to the amplified
photodetector signal. Keep the FPM-8200 in manual range mode when you use
the analog output. This is a very low-noise, stable output normalized to 10V,
representing percentage of full range. (For example: 7.1V = 71% of range). This
information is shown by the bar graph on the front panel but with greater
resolution. Since resolution is mostly determined by the instrument that you
connect it to, this output is useful for monitoring small changes. With 1000
typical output impedance, you can directly connect it to most dataloggers or digital
voltmeters. Analog output is most commonly used for relative power
measurements, or as a controlling input for automatic fiber alignment systems.
For such tests, the absolute value represented by the analog output voltage is
usually not of concern, only the change relative to a starting point.
For monitoring relative power measurements, put the meter in auto range mode to
find the appropriate gain range; then set the meter to manual range mode to avoid
changing gain ranges during the test.

Gain Range Boundaries

Understanding how gain ranges and detector response relate to analog output
can be useful in interpreting analog voltage. Gain ranges are related to the current
from the photodetector, not to direct light power, because semiconductor
photodetector response varies with wavelength.
The FPM-8200 meter has eight gain ranges. Each range increases gain by 10x
over the previous range. The analog output varies 0 V to 10 V representing
minimum to maximum current output for that range. The maximum current for
each range is:

Table 2.1 Gain Range Boundaries

Range
0
1
2
3
14
 FPM-8200
FR O N T PA N E L O P E R A T I O N
The FPM-8200 Back Panel
Maximum Current
10 mA
1 mA
100 μA
10 μA
Range Maximum Current
4 1 μA
5 100 nA
6 10 nA
7 1 nA