OPC Assistant Unknown New Measurement Error



In some cases when the OPC Assistant is used to expose a register for OPC an Unknown New Measurement error will occur when changes are saved.

Product Line
ION Enterprise 5.5
ION Enterprise 6.0
Struxureware Power Monitoring 7.0.1
Power Monitoring Expert 7.2
Power Monitoring Expert 8.0

OPC Assistant

Part of the OPC Server Assistant’s role is to create an address that maps the device and handle to a source and measurement if it is not a default register. It creates a measurement if one does not already exist and then adds the address definition to the database. The tool looks to see if a given measurement already exists before creating a new one. Measurement lookup is by a hash value; the string is converted to a number and a search is done on that number. Unfortunately the conversion from string to hash value does not guarantee a unique hash code, therefore a measurement may appear to exist when it does not. Adding the address definition will fail because it refers to a nonexistent measurement.

Within the OPC Server Assistant
1. select view\measurements
2. associate the register with an appropriate existing measurement
3. select file\export

Alternatively, change the label of the register to be exposed. This may not work if the new label chosen results in an existing hash value, so a series of new labels may have to be tried until one succeeds.