T08: Measure Limits
Constant limits, then the more useful kind — a limit whose threshold is another measure, so it tracks a changing target.
What you will build: a constant limit, a measure-driven limit that tracks a monthly target, and a limit that validates manual entry.
Time: about 25 minutes.
You need: T05 and T03 completed.
Step 1 — A constant limit#
Start with the simple case: steam flow should stay in an operating band.
In the Toolbox, create a limit called Steam Flow Band.
Attach it to Steam Flow Hourly with ranges:
| Range | Value |
|---|---|
| High | 4.6 |
| Target | 3.9 |
| Low | 3.1 |
Set the limit type to Either — this is a value that should stay inside a band, and both directions are a problem.
Compare that with Downtime Minutes Hourly, which should be a High limit: more is worse, and there is no such thing as too little downtime.
| Measure meaning | Limit type |
|---|---|
| Downtime, energy, cost, rejects | High |
| Production, availability, yield | Low |
| Temperature, pressure, pH in a band | Either |
Step 2 — Put it on the chart#
Add Steam Flow Hourly to a Time Based Chart with the Hourly constructor, then bind the limit onto it.
Remember the rule: a limit slot only accepts a limit belonging to the measure on its parent chart item. The chart must already carry that measure as a series. Add the series first, bind the limit second — attempting the reverse has nowhere to attach.
The chart now shows the operating band as reference lines. A reader no longer has to know what good looks like.
Step 3 — The problem with constants#
Now try to put a limit on Bottles Daily.
The target is 2,400,000 bottles a month, which is about 77,400 a day. So set a constant low limit at 77,400.
Next month, planning changes the target to 2,600,000. Your limit is now wrong, and it stays wrong until somebody remembers to edit it.
In a real plant with dozens of targeted measures, that editing does not happen. Dashboards quietly judge against last year's targets.
Step 4 — The better way#
A limit's threshold does not have to be a constant. It can be another measure.
Create a limit for Bottles Daily and set its low range value type to Measure, pointing at Production Target Daily — the calculated daily target from T03.
Now:
- Planning enters a new monthly target on the form
Production Target Dailyrecalculates- The limit on
Bottles Dailymoves with it - Every chart and widget updates
No limit editing, ever. This is the single most useful thing to know about Infohub limits, and it is under-used.
Hold targets as measures, not as limit constants. A target held as a manual entry measure is versioned by period, entered by the people who own it, visible on charts, and reportable in its own right. A constant limit gives you none of that. If a threshold changes with any regularity — monthly, seasonally, per product — point the limit at a measure.
The third option, Offset, expresses a threshold relative to something — a tolerance band around a target.
Step 5 — Colour a widget#
Bind the new limit onto the Production vs Target Daily widget from T05, or create a widget for Bottles Daily.
The widget now colours itself from where the value sits relative to its limits.
Never hard-code the colour. A fixed green stays green while the value goes out of specification — it looks correct on the day it is built and lies thereafter. If a colour cannot change, it should not be a status colour.
Step 6 — Validate manual entry#
An easily missed use of limits, and one of the highest value for the effort.
Put a limit on Brix — the manually entered laboratory reading from T03:
| Range | Value |
|---|---|
| High | 12.5 |
| Target | 11.5 |
| Low | 10.5 |
Type 115 instead of 11.5 into the form and watch it flag immediately.
That catches the misplaced decimal point at the moment of entry, before it propagates into a shift report, a monthly average, and a customer conversation. One limit definition per manual measure, and it is the cheapest validation available in Infohub.
Step 7 — Set thresholds that mean something#
The technical part is easy. Choosing the numbers is where limits succeed or fail.
Chart the measure over a few months first. A limit set from a design document rather than from real behaviour will either never fire or fire constantly.
Set them where you would actually act. A limit is a statement that something needs attention. If a breach prompts nobody to do anything, the limit is at the wrong value or should not exist.
Do not set them only at the specification boundary. A limit at the point where product is already out of specification tells you too late. A warning band before it gives someone a chance to intervene.
A limit that fires constantly is worse than no limit. The fastest way to make a dashboard useless is a threshold so tight that everything is always red. Readers learn within a week that red means nothing, and the genuine exception becomes invisible.
If a limit fires most of the time, either the threshold is wrong, or the process cannot meet it — and the second is a different conversation entirely.
Step 8 — Review them#
Look at each limit you have created and ask: if this fired right now, what would somebody do?
If the answer is "nothing", change the threshold or remove the limit. That question, applied honestly, removes most of what gets configured in a first pass and makes the rest worth reading.
What you have learned#
Limits turn numbers into information. A dashboard where every value is judged against a limit can be read at a glance.
Choose the type by what the measure means. High for things where more is worse, Low for less is worse, Either for a band.
Thresholds can be constants, measures, or offsets. The measure-driven kind is the one that keeps working without maintenance.
Limits bind after the series. The chart must already carry the measure.
Drive colour from limits, never by hand.
Limits validate manual entry for almost no effort.
Set thresholds where action begins, from real operating data.
Try this before moving on#
Limits vary by time scheme, which means the same measure can be judged differently on different calendars.
Once you have shifts (T09), consider whether Bottles Daily should have a different band at weekends, or whether availability should be judged differently on a maintenance shift. Most models use one set of ranges — but knowing the capability exists stops people duplicating measures to achieve it.
Next: T09: Shifts and Time Schemes — making Infohub's calendar match your plant's.