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IO sharing: use authoritative live values from a remote site

Choose the TagRef from the available catalog in a screen, script, alarm, or trend configuration. Do not build it from display names manually. An IO TagRef has this canonical form:

IO Sharing

IO Sharing: IO sharing: use authoritative live values from a remote site

IO sharing does not copy remote devices or tags and does not connect to the PLC again. It lets the current site subscribe, through stable TagRefs, to authoritative values supplied by the remote IO Owner within an explicitly selected PLC scope.

Supported scenarios

  • Read remote production state on a screen.
  • Read remote values or trigger an Integration Script from remote IO changes.
  • Feed alarms and trends through their dedicated persistent input subscriptions.
  • Share only the PLCs required by a consuming site instead of exposing the entire site.

Step 1: join the remote site and enable IO

  1. Open Sites and enter the remote HTTPS address under Search or Join Site.
  2. Verify the remote identity and connectivity, then join the site.
  3. Enable IO for that remote site. If several source nodes exist, select the one that provides IO.
  4. Return to System Status and confirm that both the remote site and IO capability are available.

Step 2: select the PLC scope to use

  1. Open PLCs and IO Domains for the remote site.
  2. Under Source Devices, select only the PLCs required by the current site.
  3. Select Preview PLC Scope Change and review additions, removals, and existing dependencies.
  4. Confirm and save. HQControl blocks a removal that would break a Screen, Tag Group, Alarm, Trend, or Script reference.

Step 3: select a stable TagRef from the catalog

Choose the TagRef from the available catalog in a screen, script, alarm, or trend configuration. Do not build it from display names manually. An IO TagRef has this canonical form:

Display names may change; the stable TagRef is the cross-site identity. After saving, verify the actual value, quality, source, and timestamp.

hq://io/<io-domain-id>/<device-uid>/<tag-uid>

Ownership and failure boundaries

  • Remote Device and Tag definitions are not copied locally.
  • Remote live values are not written to the local PostgreSQL tag_latest table.
  • A PLC still has one active IO Owner; the consumer does not open another PLC connection.
  • When the source site disconnects, consumers receive degraded quality instead of an old value presented as Good.
  • Phase 1 calculated tags cannot use remote IO TagRefs as inputs.