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An “E_UNKNOWN_ITEM_NAME” error message appears when attempting to add a PM800’s measurements in OPC Test Client. OPC tags do not show up in the ION OPC client or in ENM Alarm Sentry.


When attempting to add a PM800's measurements to a subscription in OPC test client, the error message E_UNKNOWN_ITEM_NAME appears.

Can cause OPC tags not showing up in OPC Test Client or in Alarm Sentry. In some instances, only a partial list of OPC tags is available for the device.

Product Line

StruxureWare Power Monitoring 7.0.X
Power Monitoring Expert 7.2.X, 8.x
OPC Test Client


SPM or PME as an OPC Server


Too many PM800 measurements are being tagged and exposed to the OPC server (limit of 1268 tags per device type). If the limit is exceeded, the tags will not be exposed properly for OPC clients.


Modify the DefaultMeasurements.xml file to reduce the number of OPC tags associated with a device.
Before proceeding, back up any files that will be modified in a location that will not be overwritten.
If a user initiates the "Update OPC Server" function in Management Console, any changes to the IONServicesconfiguration.xml file will be overwritten.

  1. Locate the DefaultMeasurements.xml file in:
(Installation Drive):\Program Files (x86)\Schneider Electric\Power Monitoring Expert\system\IONServices 
OR (Installation Drive):\Program Files (x86)\Schneider Electric\ION Enterprise\system\IONServices
Create a backup of the .xml file in a separate location.

Before proceeding, check to see if a copy of DefaultMeasurements.xml has been saved in the ~\config\IONServices folder. If so, backup the original DefaultMeasurements.xml file from the ~\system\IONServices folder and move the file from the ~\config/IONServices folder into the ~\system\IONServices folder. It is not recommended to save the DefaultMeasurements.xml file in the ~\config\IONServices folder, as an extension folder is required to add OPC for newer device types.
  1. ​Open DefaultMeasurements.xml with Notepad and find the device type that is not displaying OPC tags.
The PM800 series meters would look similar to: 
        <MT name="PM800-IO">
            <Ctxt label="Auxiliary IO">
                <Ctxt label="Module A - PM8M22">
Reduce the number of PM800 measurements by commenting out unnecessary measurements. See the Comments section below for more information on how to perform this.
Commenting out the PM800's Spectral Measurements has been known to resolve this issue, as it can lower the tag count to less than 1268. The Spectral Measurements quantities are rarely used by the end users and as such, can be removed without impacting the rest of the system.
The Spectral Components section should look like the following:
<Ctxt label="Spectral Components">
                <Ctxt label="FFT Enable Status">
                    <M name="FFT Enable Status" label="FFT Enable Status"/>
                <Ctxt label="FFT Hold Time">
                    <M name="FFT Hold Time" label="FFT Hold Time"/>

Save the file after all changes have been made.
  1. Delete IONServicesConfiguration.xml from ~\config\IONServices. WARNING: Deleting this file will delete any previously exposed OPC tags. Create a backup of the IONServicesConfiguration.xml file and ensure your system is prepared for a loss of PC tags prior to deleting the file.
  2. ​In Management Console, select Tools > System > Update OPC Server.
  3. Attempt to add a PM800 measurement in OPC test client. The measurements should be added without an error message.


Note that deleting or commenting out a measurement will prevent it from being tagged and exposed to the OPC server.

You can comment out text in .xml documents by adding <--! ... --> to the section you want to comment out.
For example:
This text
would be commented

Alternative Solution: DefaultMeasurements.xml in the ~\system\IONServices folder can be replaced, which will also resolve the issue. Use the .xml file attached to this KB as the replacement. This copy has had the Spectral Measurements commented out.
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