I was wondering what Interface would be suitable for user entry into pi tags.
The values for the tags would be entered by the user.
If you can use PI Vision + custom symbol, then following symbols can also write values to PI. Remember that these custom symbols are not official one. PI Manual Logger is OSIsoft's official tool for manual entry.
PI Coresight 2016 R2 Put Value Custom Symbol by PI Web API
The PI Developers Club pod @ UC 2017
Also PI DataLink contains write data function. It can call piputval(). See livelibrary for more details
Have you looked at PI Manual Logger? Without knowing what your particular requirements are, I would suggest this product as the first option to look at.
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