Absolute Power measurement error observed with an in-line power meter

Applies to

PPM-350 Series, OX1, OTDR in-line power meters


When using an in-line power meter for absolute power measurements in dBm or milliwatt, you suspect an error. This article applies to both small and large possible errors.

Troubleshooting steps

Possible Cause 1: There is a soiled or damaged connector

Proposed Solution:


  • The PPM and other in-line power meters use a physical contact connector. This connector as well as the connector of your patch cord must be clean and in good condition, otherwise significant error could be introduced.
  •    Inspect the connector and if cleaning is not sufficient, the unit may need to be returned (RMA) for a connector replacement (-CR).


Possible Cause 2: APC vs UPC connector types.

Proposed Solution:

  • Ensure that the fiber you are connecting to the EXFO in-line power meter, is compatible to the connector type fitted to the unit.



Possible Cause 3: The EUI is damaged.

Proposed Solution:

  • EUI = EXFO universal adapter and is the part fitted to the optical ports of your power meter


  • As for any adapter, the EXFO EUI has an internal ceramic sleeve to ensure precise fiber-to-fiber alignment. Should the sleeve be damaged, a large error may be observed.
  • Try another EUI if available. This is a common part used on many EXFO instruments, so there is a good chance you may have one available.


Possible Cause 4: Other possible causes

Proposed Solution:

  • Check other published knowledge articles that address potential error sources for all optical power meters, both in-line and standard power meters.
  • You will find these in the related articles, or by searching absolute power measurement error.