EXFO EPM-500 Power Meter - Manual (Page 15)

EPM-500/ELS-500/EOT-500 10
4 Measuring Power or Loss
(EPM-500 and EOT-500)
Nulling Electrical Offsets
Temperature and humidity variations affect the performance of electronic circuits
and optical detectors. Nulling the electrical offsets eliminates these effects. Your unit
has been designed not to require offset nulling under normal operation, but you
should perform it whenever environmental conditions change significantly or when
measuring very low power values.
Note: Factory-defined values will be reinstated when you turn off the unit.
To perform an offset nulling:
Hold down
a few seconds. The unit displays NULL
while nulling the offsets, then returns to normal mode.
Note: Keypad is disabled during the operation.
I
MPORTANT
If light reaches the detector when nulling offsets, LIGH appears on
the display and the nulling is not performed. You will need to press a
key to return to the previous display.