Applicable Systems
GP4000 Series
Symptoms
The HMI displays ### or ---- for a numeric tag instead of the actual value. The tag quality shows Bad or Uncertain.
Possible Causes
- PLC tag address changed after program modification without updating the HMI project
- Tag data type mismatch between PLC and HMI (e.g., Int vs. Real)
- Tag addressing mode set incorrectly (e.g., symbolic vs. absolute)
- PLC communication driver incompatible with the tag addressing scheme
Troubleshooting Steps
- Step 1: Verify the tag address in the PLC program matches the HMI tag configuration
Update the HMI project if the PLC tag address has changed - Step 2: Check that the tag data types match between PLC and HMI
Convert the tag type in the HMI project to match the PLC definition - Step 3: Verify the addressing mode: symbolic (named) or absolute (address-based)
Switch modes in the HMI driver settings to match the PLC configuration - Step 4: Test the tag by forcing a known value in the PLC and observing the HMI display
If the forced value displays correctly, the addressing is fixed
How to Reset
Reset: The tag value displays normally once the addressing is corrected and the project is re-downloaded.
Frequently Asked Questions
- Q: Why does my tag show ###?
The value exceeds the display format width, or the tag quality is Bad. Check the numeric format and PLC communication.
- Q: What is tag quality?
An OPC concept indicating data reliability: Good (valid), Bad (no data), or Uncertain (stale or questionable).
- Q: How do I change the tag data type?
In the HMI configuration software, open the tag properties and select the correct type. Redownload the project to the HMI.
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Source: OEM Technical Manual
Category: HMI
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