How do I ignore negative values on a Honeywell paperless recorder?


When you’re dealing with process recorder functions, some actions don’t like negative values, like a totalizer that sees a negative offset at zero flow as backflow, which impacts the total. But on the Honeywell X-Series paperless recorders, you can work around the issue, so they report only the positive values.

To report negative values as zero and pass positive values through as-is, use Honeywell’s over math expression (pen > Edit Maths = math statement).  The expression  over[x,y]   returns x if x is larger than y. Otherwise it returns zero.

Either round or square brackets work in the expression. For example,
    Edit Maths = over[uv1,0] or  Edit Maths = over(uv1,0)

 The screen shots below show a pen’s Edit Maths statement using over


 

Any negative value in the user variable (uv1) is reported as zero.   Any positive value in the user variable (uv1) is reported as found.

To read typical analog inputs, use an expression like  over[A4,0]

To read Modbus values, use an expression like   over([SCV1,1,1],0)

Note: This will require use of six firmware credits in your recorder for Full Maths, since it is not part of the basic math functionality.

You’ll find more information in the Honeywell X-Series recorder user manual, Appendix B: Full Maths and Script Processing. Learn more about Honeywell paperless recorders at Lesman.com

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