We are logging temperature in Celsius with tag history. Our HMI allows clients to select their preferred units of measure and all displayed values are run through functions to display in selected units of measure. I’d like to extend this to the EasyChart and thought we could use a calculated pen for Fahrenheit and just show/hide the two pens through scripting to match each Vision client’s selected units of measure for temperature. Unfortunately, I can’t find a way to make the necessary calculation ( * 9/5 + 32). At first I thought we could do one part in one calculated pen and then the next step in another calculated pen, but it appears calculated pens may not be based on other calculated pens.
Of course we can create an expression tag to do the real-time calculation and then log tag history for it too, but I’m wondering if there’s a reasonable way to display a calculated conversion from tag history rather than store the same data in two different units of measure. Any suggestions?