– 8 –
OPERATING PROCEDURES
Reading the display
The Fiber Optic Test Set contains a digital radiometer which converts optical power to
an electrical signal shown numerically on the digital LCD display. The unit of measure is
watts expressed as a decimal. For example, 1 milliwatt (mW) = 1/1000th of a watt which
is expressed as .001 watts in decimal form. The “Display Selector Switch” moves the
decimal point automatically so that readings are always related to a signifi cant increment of
Watts. So a reading of 1.000 on the 2 mW range would represent 1.000 mW.
The display on the Fiber Optic Test Set is designed to respond in a
linear scale
, meaning
that doubling the optical power will produce a numerical reading twice as large. This
type of scaling has an advantage when trying to observe small differences in power while
maintaining maximum display sensitivity.
Connecting cables to the “ST
®
” receptacles
The Fiber Optic Test Set receptacles can accept an industry-standard “ST
®
” fi ber optic
connector, an un-connectorized plastic fi ber cable, or a bare fi ber. ST
®
connectors are
available for a variety of fi ber cable core/cladding sizes. When attaching a connector to a
fi ber optic cable, follow the manufacturer’s instructions carefully.
Make certain the fi ber
end does not protrude beyond the end of the connector ferrule, or damage to internal
components of the test set may occur.
If you are not using a connectorized cable, note that the receptacle has an internal diameter
of 2.5 mm. This provides a good fi t for a 1000 µm (1 mm) core, plastic jacketed fi ber
optic cable, which has an overall outside diameter of 2.2 mm. For best results, the cable
end should be prepared by cutting with an appropriate tool such as those available from
Industrial Fiber Optics.
When measuring an un-connectorized fi ber or cable with a diameter smaller than 2.2
mm, some type of sleeve should be used to make up the difference. In all cases the fi ber
end should be properly prepared by cleaving, cutting, or polishing as recommended by the
fi ber or connector manufacturer. An unprepared or damaged fi ber end will spray light in
unintended directions, resulting in power loss and inaccurate readings.
