A useful engineering value has more than a number. It has an equation, identified inputs, a unit, and a relevant period.
Make your measurement procedure explicit.
A raw channel may need a baseline correction, scale factor, or instrument-specific equation before it is ready for review. SanSignal calculated variables let you define that transformation on the instrument, using decimal inputs and named calibration constants.
Select the actual inputs through the expression editor so the relationship is tied to their identities. Give the output a useful label and the unit specified by your procedure. The incoming value and the calculated result remain separate variables, allowing reviewers to inspect both when a result needs explanation.
Bring related channels into the equation.
Some calculations use channels on the same instrument; others need a reference from elsewhere in the project. SanSignal supports active decimal inputs from other instruments and can use calculated variables as dependencies, provided the dependency graph remains active and cycle-free.
Cross-instrument inputs need a deliberate time relationship. A past buffer controls how far back an external input may look. Set that buffer around the source cadence and your method, then inspect periods where a reference was unavailable. The existence of a value somewhere in history does not make it the right input for the current reading.
- Use calibration constants for instrument-specific parameters.
- Reference other project instruments when the method requires them.
- Inspect missing inputs and calculation dependencies during commissioning.
Give changes a defined place in time.
A monitoring program may change its intended equation at a known point. Use one equation for the full history, or define equations over time with inclusive start times and an optional fallback. This lets the configuration reflect a deliberate change in the measurement procedure.
Before changing a period or a constant, identify the readings that should be affected and keep a known value for comparison. Verify results on both sides of the change. A calibration update and a new reporting label are different operations; changing the unit label alone does not convert stored numbers.
Follow the calculation through to its result.
Creating or changing computation can trigger a historical rebuild. SanSignal exposes the linked run so the team can see its progress and investigate errors. Check that rebuild before using the new values in a dashboard, anomaly definition, or downstream workflow.
Previous current values remain visible while recalculation runs, and also remain if a rebuild fails. Treat status as part of the review: a visible graph is not proof that a newly edited equation has finished. After completion, compare representative outputs with an independently checked example from your measurement procedure.
Common questions.
Can we use an input from a different instrument?
Yes, calculated variables can reference active decimal variables from another instrument in the same project. Configure the past buffer and verify the behavior when that source has gaps.
Can a calculation change from a particular date?
Yes. Equations over time supports calculation periods with unique inclusive start times and an optional undated fallback. Inspect both sides of the period boundary after recalculation.